Πέλλετ ξύλου

Τα πέλλετ ή συσσωματώματα ξύλου είναι είδος φιλικού προς το περιβάλλον καυσίμου που προέρχεται απόξύλο ή από βιομάζα, γενικά. Κατασκευάζονται κυρίως από πριονίδι ή άλλα απόβλητα από πριστήρια και μονάδες επεξεργασίες ξύλου (π.χ. θρύμματα ξύλου, ξακρίδια κ.λπ.). Σε αρκετές περιπτώσεις παράγονται και από εναλλακτικές πρώτες ύλες βιομάζας, όπως είναι το [πυρηνόξυλο], οι ενεργειακές καλλιέργειες, τα κλαδέματα δέντρων (π.χ. ελιάς και τα υπολείμματα καλλιεργειών

http://www.interscala.gr

Παραγωγή

Η διαδικασία παραγωγής των "πέλλετ ξύλου" περιλαμβάνει διαδοχικά τα ακόλουθα στάδια ^[2]: 1) την αποθήκευση των πρώτων υλών [βιομάζας/βιομάζα] σε καθαρό και στεγνό χώρο 2) τη ξήρανση της ώστε να μειωθεί η περιεκτικότητά της σε υγρασία 3) τον τεμαχισμό και άλεση της 4) τη συμπίεση της σε ειδικές [πρέσες/πρέσα] 5) τη ψύξη και την κοσκίνιση του παραγόμενου πέλλετ 6) την αποθήκευση του τελικού εναλλακτικού καυσίμου που παράγεται σε ασφαλές μέρος. Βασική προϋπόθεση σε όλη αυτή τη διαδικασία είναι η πρώτη ύλη να αποτελείται αποκλειστικά από καθαρό ξύλο, χωρίς προσμίξεις από χημική ουσία (π.χ. βαφές, βερνίκια, κ.λπ.) Παράλληλα, κατά την παραγωγή τους δεν χρησιμοποιούνται καθόλου χημικά, καθώς η συγκολλητική ουσία που τους χαρίζει τη συμπαγή τους μορφή, είναι η λιγνίνη, μια φυσική ουσία που περιέχεται στο ξύλο. Η διαδικασία παραγωγής του πέλλετ συντελεί στην παραγωγή υψηλής ποιότητας προϊόντος είναι απαραίτητο να ελέγχεται πλήρως η παραγωγική διαδικασία. Οποιαδήποτε μεταβολή στις συνθήκες παραγωγής του πέλλετ (π.χ. μη επαρκής ξήρανση) έχει ως συνέπεια την παραγωγή κατώτερης ποιότητας προϊόντος, με χαμηλότερη ενεργειακή απόδοση.

Χαρακτηριστικά των πέλλετ ξύλου

Ως προς την μορφή τους, τα πέλλετ ξύλου έχουν μικρό, κυλινδρικό σχήμα και λεία εξωτερική επιφάνεια. Αυτά τα χαρακτηριστικά τους προσδίδουν ιδιότητες ρευστό (μεγάλη ευκολία στη ροή). Συνεπώς, η αποθήκευση και μεταφορά της είναι πολύ πιο εύκολη και αποδοτική από οποιαδήποτε άλλο είδος ξύλου. ^[3] Βασικό χαρακτηριστικό του πέλλετ είναι η πολύ χαμηλή υγρασία του, η χαμηλή του περιεκτικότητα σε τέφρα (στάχτη) και η υψηλή ενεργειακή του πυκνότητα. Όλα αυτά τα χαρακτηριστικά το καθιστούν εξαιρετικά ελκυστικό και αποδοτικό καύσιμο. Οι παραπάνω ιδιότητες των πέλλετ ξύλου, έχουν αποτυπωθεί και στο Ευρωπαϊκό Πρότυπο ποιότητας "ΕΝ 14961-2", που καθορίζει αυστηρά όρια στις ιδιότητες των πέλλετ ξύλου. Σύμφωνα με το εν λόγω πρότυπο, τα πέλλετ ξύλου διακρίνονται σε τρεις κατηγορίες: Α1, Α2 και Β. Οι αυστηρότερες προδιαγραφές αντιστοιχούν στα ποιότητας Α1 πέλλετ ξύλου, τα οποία αποτελούν εξαιρετικής ποιότητας καύσιμο και ιδανικό για οικιακή κατανάλωση

Ρωσία

Η Ρωσική Ομοσπονδία (ρωσική: Росси́йская Федера́ция, ΔΦΑ: [rɐˈsʲijskəjə fʲɪdʲɪˈrat͡sɨjə]), η Ρωσία (Росси́я προφέρεται σύμφωνα με το ΔΦΑ [rɐˈsʲijə]) είναι το μεγαλύτερο σε έκταση κράτος της γης, με έκταση 17.075.200 χλμ². Ο πληθυσμός της ανέρχεται σε 143.030.106 κατοίκους, σύμφωνα με εκτιμήσεις για το 2012[2]. Πρωτεύουσα της χώρας είναι η Μόσχα. Η επίσημη γλώσσα είναι τα ρωσικά και νόμισμα το ρούβλι. Διοικητικά διαιρείται σε 83 ομοσπονδιακά υποκείμενα, τα οποία είναι ομαδοποιημένα σε επτά διαμερίσματα. Η Ρωσική Ομοσπονδία δημιουργήθηκε το 1991 και προήλθε από την αποδόμηση της Ε.Σ.Σ.Δ.. Έκτοτε, το πολίτευμά της είναι Προεδρική Ομοσπονδιακή Δημοκρατία κατά το πρότυπο του δυτικού φιλελεύθερου μοντέλου.Η Ρωσική Ομοσπονδία καταλαμβάνει μεγάλο μέρος της ανατολικής Ευρώπης και ολόκληρη τη βόρεια Ασία. Από δυσμάς προς ανατολάς συνορεύει με τη Νορβηγία, τη Φινλανδία, την Εσθονία, τη Λετονία, τη Λιθουανία, την Πολωνία, τη Λευκορωσία, την Ουκρανία, τη Γεωργία, το Αζερμπαϊτζάν, το Καζακστάν, τη Μογγολία, την Κίνα και τη Βόρεια Κορέα.Αποτελείται κυρίως από τεράστιες πεδινές περιοχές, στέπες στα νότια, και πυκνά δάση και τούνδρα στα βόρεια. Οι περιοχές αυτές αποτελούν και το 10% των παγκόσμιων αγροτικών εκτάσεων.Οι σημαντικότερες οροσειρές της Ρωσίας είναι ο Καύκασος (εκεί βρίσκεται το Ελμπρούς, το ψηλότερο βουνό της Ρωσίας), τα Ουράλια και τα Αλτάι.Επίσης, δεκάδες χιλιάδες ποτάμια διαρρέουν τη Ρωσία, με τον Βόλγα να είναι το πιο γνωστό, επειδή είναι το μακρύτερο ποτάμι της Ευρώπης, αλλά και για την ιστορική του σημασία. Μεγαλύτεροι ποταμοί είναι ο Βόλγας, ο Ντβίνα, ο Ντον, o Ομπ, ο Γενισέης, ο Αγγαράς, ο Λένας και ο Αμούρ.Το ισχύον Σύνταγμα της Ρωσικής Ομοσπονδίας (στα ρωσικά: Конститу́ция Росси́йской Федера́ции, εγκρίθηκε (με το 54,5% των ψηφοφόρων να ψηφίζουν υπέρ) έπειτα από δημοψήφισμα στις 12 Δεκεμβρίου του 1993. Αντικατέστησε το σοβιετικό Σύνταγμα του 1978.Σύμφωνα με το σύνταγμα αυτό, το ρωσικό κοινοβούλιο έχει δύο νομοθετικά σώματα: το Συμβούλιο της Ομοσπονδίας (Άνω Βουλή), που αποτελείται από εκπροσώπους των περιφερειακών διοικητικών μονάδων της Ρωσικής Ομοσπονδίας, που αποκαλούνται «γερουσιαστές», και την Κρατική Δούμα (Κάτω Βουλή) με 450 μέλη, που εκλέγονται με 4ετή θητεία με βάση τον πληθυσμό κάθε περιοχής. Η λέξη "δούμα" προέρχεται από το ρήμα dumaju, που σημαίνει «σκέπτομαι».Οι αποφάσεις της Δούμας επικυρώνονται από τον Πρόεδρο και το Συμβούλιο της Ομοσπονδίας. Ο Πρωθυπουργός διορίζεται από τον Πρόεδρο με τη σύμφωνη γνώμη της Κάτω Βουλής. Ο Πρόεδρος εκλέγεται με άμεση ψηφοφορία για 6 έτη και έχει ισχυρές εξουσίες. H παράταση της θητείας του προέδρου από 4 χρόνια σε 6 χρόνια εγκρίθηκε από την Άνω Βουλή στις 22 Δεκεμβρίου του 2008

Μάχη της Μόσχας

Η Μάχη της Μόσχας (ρώσικα: Битва под Москвой, γερμανικά: Schlacht um Moskau) είναι το όνομα που έχει δοθεί από σοβιετικούς ιστορικούς σε δύο περιόδους σημαντικών μαχών κατά μήκος ενός τομέα 600 χιλιομέτρων στο Ανατολικό Μέτωποκατά την διάρκεια του Β' Παγκοσμίου Πολέμου. Διαδραματίστηκε μεταξύ Οκτωβρίου 1941 και Ιανουαρίου 1942. Ο Χίτλερθεωρούσε την Μόσχα -πρωτεύουσα της Σοβιετικής Ένωσης και μεγαλύτερη πόλη της- κύριο στρατηγικό στόχο των δυνάμεων του Άξονα στην Επιχείρηση Μπαρμπαρόσα.

Η γερμανική επίθεση είχε την κωδική ονομασία Επιχείρηση Τυφώνας και είχε στόχο την δημιουργία δύο σφηνών, μία βορείως της Μόσχας εναντίον του Μετώπου Καλίνιν από την 3η και την 4η Ομάδα Πάντσερ, αποκόπτοντας ταυτόχρονα την σιδηροδρομική γραμμή Μόσχας-Λένινγκραντ, και μία νοτίως της Μόσχας εναντίον του Δυτικού Μετώπου, νότια από τηνΤούλα από την 2η Στρατιά Πάντσερ, ενώ η 4η Στρατιά θα προωθούνταν κατευθείαν προς την Μόσχα από τα δυτικά. Ένα ξεχωριστό επιχειρησιακό σχέδιο των Γερμανών, με την κωδική ονομασία Επιχείρηση Βόταν, συμπεριλήφθηκε στην τελική φάση της γερμανικής επίθεσης.

Αρχικά οι σοβιετικές δυνάμεις αμύνθηκαν στην περιφέρεια της Μόσχας κατασκευάζοντας τρεις αμυντικές ζώνες και αναπτύσσοντας νέες επίστρατες εφεδρείες καθώς και στρατεύματα από την Σιβηρία και την Άπω Ανατολή. Εν συνεχεία, αφού αναχαιτίστηκε η γερμανική επίθεση, ξεκίνησε η σοβιετική αντεπίθεση και διάφορες μικρότερης κλίμακας επιθέσεις ώστε να εξαναγκαστούν οι γερμανικές δυνάμεις να υποχωρήσουν σε θέσεις γύρω από τις πόλεις Οριόλ, Βυάζμα καιΒιτέμπσκ, σχεδόν περικυκλώνοντας τρεις γερμανικές στρατιές στην πορεία.

Το αρχικό σχέδιο κεραυνοβόλου πολέμου, το οποίο είχε την κωδική ονομασία Επιχείρηση Μπαρμπαρόσα, προέβλεπε την κατάληψη της Μόσχας σε τέσσερις μήνες. Όμως, παρά την μεγάλη αρχική προώθηση, η Βέρμαχτ επιβραδύνθηκε λόγω της σοβιετικής αντίστασης (πιο συγκεκριμένα στην Μάχη του Σμολένσκ, η οποία διήρκεσε από τον Ιούλιο μέχρι τον Σεπτέμβριο του 1941 και καθυστέρησε την επίθεση στην Μόσχα κατά δύο μήνες). Μόλις η Βέρμαχτ εξασφάλισε το Σμολένσκ, επέλεξε να ανασυντάξει της δυνάμεις της γύρω από τοΛένινγκραντ και το Κίεβο, καθυστερώντας περαιτέρω την επίθεση στη Μόσχα. Η προώθηση των δυνάμεων του Άξονα ξεκίνησε ξανά στις 2 Οκτωβρίου 1941 με την επίθεση που έφερε την κωδική ονομασία Επιχείρηση Τυφώνας, με σκοπό την κατάληψη της Μόσχας πριν την έλευση του χειμώνα.

Μετά από μια προώθηση που οδήγησε στην περικύκλωση και την καταστροφή αρκετών σοβιετικών στρατιών, οι Γερμανοί αναχαιτίστηκαν στη γραμμή άμυνας του Μοζάισκ, μόλις 120 χιλιόμετρα από την Μόσχα. Έχοντας διαρρήξει τη σοβιετική άμυνα, η επίθεση της Βέρμαχτ επιβραδύνθηκε από τις καιρικές συνθήκες, αφού οι φθινοπωρινές βροχές κάλυπταν τους δρόμους και τα πεδία με παχιά λάσπη που παρακώλυαν σημαντικά τα οχήματα του Άξονα, τα άλογα και τους στρατιώτες. Παρόλο που το ξέσπασμα του χειμώνα και το πάγωμα του εδάφους επέτρεψαν στις δυνάμεις του Άξονα να συνεχίσουν να προωθούνται, είχαν να αντιμετωπίσουν ολοένα αυξανόμενη σοβιετική αντίσταση.

Στις αρχές Δεκεμβρίου, οι προωθημένες ομάδες Πάντσερ απείχαν λιγότερο από 30 χιλιόμετρα από το Κρεμλίνο, και οι αξιωματικοί της Βέρμαχτ μπορούσαν να δουν κάποια από τα κτίρια της Μόσχας με κιάλια. Παρόλα αυτά οι δυνάμεις του Άξονα δεν ήταν ικανές να προωθηθούν περαιτέρω. Στις 5 Δεκεμβρίου 1941 νέες σοβιετικές δυνάμεις από την Σιβηρία, εκπαιδευμένες στις χειμερινές επιχειρήσεις, επιτέθηκαν στις γερμανικές δυνάμεις στο μέτωπο της Μόσχας. Μέχρι τον Ιανουάριο του 1942 οι Σοβιετικοί είχαν απωθήσει την Βέρμαχταπό 100 έως 250 χιλιόμετρα από τη Μόσχα, απομακρύνοντας την άμεση απειλή κατά της Μόσχας. Οι δυνάμεις του Άξονα δεν πλησίασαν ποτέ ξανά τόσο κοντά στη σοβιετική πρωτεύουσα.

Η Μάχη της Μόσχας ήταν μία από πλέον σημαντικές μάχες του Β' Παγκοσμίου Πολέμου, κυρίως επειδή οι Σοβιετικοί κατάφεραν να εμποδίσουν την πιο σοβαρή απόπειρα κατάληψης της πρωτεύουσάς τους. Η μάχη ήταν μία από τις μεγαλύτερες όλου του πολέμου, με περισσότερες από 1.000.000 απώλειες. Αποτέλεσε σημείο καμπής, καθώς ήταν η πρώτη φορά από το 1939, οπότε ξεκίνησε τις πολεμικές επιχειρήσεις η Βέρμαχτ, που υποχρεώθηκε σε μεγάλης κλίμακας υποχώρηση. Η Βέρμαχτ είχε αναγκαστεί να υποχωρήσει και νωρίτερα, κατά τη διάρκεια της Επίθεσης Γιέλνια τον Σεπτέμβριο του 1941 και κατά την διάρκεια της Μάχης του Ροστόφ (η οποία ήταν η αιτία να χάσει ο φον Ρούντστεντ τη διοίκηση των γερμανικών δυνάμεων της ανατολής), αλλά αυτές οι υποχωρήσεις ήταν ήσσονος σημασίας συγκρινόμενες με αυτήν της Μόσχας.

Στις 22 Ιουνίου 1941, τα γερμανικά, ρουμάνικα και σλοβάκικα στρατεύματα εισέβαλαν στην Σοβιετική Ένωση, εν συνεχεία την εισβολή συνέδραμε και η Ουγγαρία (μετά τον βομβαρδισμό της ουγγρικής πόλης Κάσα), ξεκινώντας αποτελεσματικά τηνΕπιχείρηση Μπαρμπαρόσα. Έχοντας καταστρέψει το μεγαλύτερο μέρος της Σοβιετικής Αεροπορίας στο έδαφος, οι γερμανικές δυνάμεις προωθήθηκαν γρήγορα βαθιά μέσα στη σοβιετική επικράτεια χρησιμοποιώντας τακτικές κεραυνοβόλου πολέμου. Οι τεθωρακισμένες μονάδες κινήθηκαν ταχύτατα δημιουργώντας σφήνες, περικυκλώνοντας και καταστρέφοντας ολόκληρες σοβιετικές στρατιές. Ενώ η γερμανική Ομάδα Στρατιών Βορρά κινούνταν προς το Λένινγκραντ, η Ομάδα Στρατιών Νότου επρόκειτο να καταλάβει την Ουκρανία, ενώ η Ομάδα Στρατιών Κέντρου προωθήθηκε προς την Μόσχα. Οι σοβιετικοί αμυνόμενοι κατατροπώθηκαν, ενώ ο Κόκκινος Στρατός είχε σημαντικές απώλειες.

Το Ιούλιο του 1941, η Ομάδα Στρατιών Κέντρου είχε καταφέρει να περικυκλώσει αρκετές σοβιετικές στρατιές γύρω από τοΜινσκ κατά την διάρκεια της Μάχης του Μπιάλιστοκ - Μίνσκ, δημιουργώντας ένα τεράστιο ρήγμα στις σοβιετικές γραμμές (το οποίο οι Σοβιετικοί δεν μπορούσαν να πληρώσουν αμέσως, καθώς δεν είχαν διαθέσιμες εφεδρείες) και διαλύοντας τοΣοβιετικό Δυτικό Μέτωπο ως οργανωμένο σώμα. Έτσι η Βέρμαχτ κατάφερε να διασχίσει τον Δνείπερο που βρίσκονταν στον δρόμο για την Μόσχα, με τις ελάχιστες δυνατές απώλειες.^[5]

Τον Αύγουστο του 1941 οι γερμανικές δυνάμεις κατέλαβαν την πόλη Σμολένσκ, σημαντικό προπύργιο στον δρόμο για την Μόσχα. Το Σμολένσκ θεωρούνταν ιστορικά το κλειδί της Μόσχας επειδή έλεγχε το πέρασμα μεταξύ των ποταμών Ντβίνα, Δνείπερο και μερικών άλλων, επιτρέποντας τη γρήγορη προώθηση στρατευμάτων χωρίς να είναι αναγκαίο να κατασκευαστούν γέφυρες στους εν λόγω ποταμούς. Η απεγνωσμένη υπεράσπιση της περιοχής του Σμολένσκ από τους Σοβιετικούς κράτησε δύο μήνες, από τις 10 Ιουλίου μέχρι τις 10 Σεπτεμβρίου 1941.^[6] Αυτή η σφοδρή μάχη, γνωστή ωςΜάχη του Σμολένσκ, καθυστέρησε την προέλαση των Γερμανών μέχρι τα μέσα Σεπτεμβρίου, αποδιοργανώνοντας την τακτική του κεραυνοβόλου πολέμου και αναγκάζοντας την Ομάδα Στρατιών Κέντρου να χρησιμοποιήσει σχεδόν τις μισές της εφεδρείες (10 από τις 24 μεραρχίες) κατά την διάρκεια της μάχης.^[6]

Η γερμανική προέλαση είχε βαλτώσει και στα υπόλοιπα σημεία του μετώπου. Κοντά στο Λένινγκραντ, η Ομάδα Στρατιών Βορρά είχε συγκρατηθεί από την αμυντική γραμμή στον Λούγκα για σχεδόν ένα μήνα, προτού την υπερκεράσει. Στο νότο, η Ομάδα Στρατιών Νότου, η οποία συμπεριλάμβανε πολλές Ουγγρικές και Ρουμάνικες μονάδες, λιγότερο εκπαιδευμένες, εξοπλισμένες και έμπειρες από τις αντίστοιχες της Βέρμαχτ, αντιμετώπισε πολλές σοβαρές αντεπιθέσεις και αναγκάστηκε να σταματήσει. Η Βέρμαχτ βρισκόταν πλέον σε δίλημμα, η Ομάδα Στρατιών Κέντρου ήταν ακόμα αρκετά δυνατή ώστε να προσεγγίσει την Μόσχα, αλλά μια τέτοια προέλαση θα δημιουργούσε έξαρμα στις γερμανικές γραμμές, αφήνοντάς το ευάλωτο σε τυχόν πλευρικές επιθέσεις του Κόκκινου Στρατού. Επιπλέον, σύμφωνα με τον Χίτλερ, η Γερμανία χρειαζόταν τον σιτοβολώνα και τους ορυκτούς πόρους της Ουκρανίας.^[7] Έτσι η Βέρμαχτ διατάχθηκε να εξασφαλίσει πρώτα την περιοχή της λεκάνης του Ντόνετς και να προωθηθεί μετά προς την Μόσχα.^[8] Η Στρατιά Πάντσερ του Χάιντς Γκουντέριαν στράφηκε προς τον νότο ώστε να υποστηρίξει την επίθεση του Γκερντ φον Ρούντστεντ στο Κίεβο,^[7] η οποία αποτέλεσε άλλη μία σημαντική νίκη εναντίον του Κόκκινου Στρατού. Στις 19 Σεπτεμβρίου 1941, οι σοβιετικές δυνάμεις αναγκάστηκαν να εγκαταλείψουν το Κίεβο μετά από την επίμονη άρνηση του Στάλιν να επιτρέψει την απόσυρση των Σοβιετικών από την προεξοχή του Κιέβου, όπως μνημονεύουν ο Αλεξάντρ Βασιλιέφσκι και ο Γκεόργκι Ζούκοφ στα απομνημονεύματά τους.^[9][10] Αυτή η άρνηση στοίχισε στον Ζούκοφ την θέση του ως Αρχηγού του Γενικού Επιτελείου,^[11] παρόλο που η πρόβλεψή του για περικύκλωση από τους Γερμανούς αποδείχτηκε σωστή. Αρκετές σοβιετικές στρατιές περικυκλώθηκαν και εξουδετερώθηκαν από την Βέρμαχτ με ένα διπλό κυκλωτικό ελιγμό, δίνοντας την δυνατότητα στις γερμανικές δυνάμεις να κινηθούν προς το νότο.^[12]

Παρά την αποφασιστική νίκη του Άξονα, η Μάχη του Κιέβου έβγαλε τον «κεραυνοβόλο πόλεμο» περαιτέρω εκτός σχεδίου. Όπως έγραψε αργότερα ο Γκουντέριαν, «Το Κίεβο ήταν σίγουρα λαμπρή τακτική επιτυχία, αλλά το ερώτημα κατά πόσο ήταν στρατηγικής σημασία παραμένει. Τα πάντα τώρα εξαρτώνταν από την ικανότητά μας να πετύχουμε τα αναμενόμενα αποτελέσματα πριν τον χειμώνα και πριν τις βροχές του φθινοπώρου.»^[13] Ο Χίτλερ πίστευε ακόμα ότι η Βέρμαχτ είχε πιθανότητες καταλαμβάνοντας τη Μόσχα, να τελειώσει τον πόλεμο πριν τον χειμώνα. Στις 2 Οκτωβρίου 1941, η Ομάδα Στρατιών Κέντρου υπό την διοίκηση του Φέντορ φον Μποκ εξαπέλυσε την τελική της επίθεση κατά της Μόσχας με την κωδική ονομασία Επιχείρηση Τυφώνας. Ο Χίτλερ είπε λίγο μετά την επίθεση ότι «Μετά από τρεις μήνες προετοιμασιών, έχουμε επιτέλους την πιθανότητα να συντρίψουμε τον εχθρό πριν την έλευση του χειμώνα. Όλες οι πιθανές προετοιμασίες έχουν γίνει…, σήμερα ξεκινά η τελευταία μάχη του χρόνου….»

Specific gravity

Specific gravity is the ratio of the density of a substance to the density (mass of the same unit volume) of a reference substance.Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for liquids or air for gases. Temperature and pressure must be specified for both the sample and the reference. Pressure is nearly always 1 atm equal to 101.325 kPa. Temperatures for both sample and reference vary from industry to industry. In British brewing practice the specific gravity as specified above is multiplied by 1000.^[1] Specific gravity is commonly used in industry as a simple means of obtaining information about the concentration of solutions of various materials such as brines, hydrocarbons, sugar solutions (syrups, juices, honeys, brewers wort, must etc.) and acids.

Specific gravity, as it is a ratio of densities, is a dimensionless quantity. Specific gravity varies with temperature and pressure; reference and sample must be compared at the same temperature and pressure, or corrected to a standard reference temperature and pressure. Substances with a specific gravity of 1 are neutrally buoyant in water, those with SG greater than one are denser than water, and so (ignoring surface tension effects) will sink in it, and those with an SG of less than one are less dense than water, and so will float. In scientific work the relationship of mass to volume is usually expressed directly in terms of the density (mass per unit volume) of the substance under study. It is in industry where specific gravity finds wide application, often for historical reasons.

True specific gravity can be expressed mathematically as:

where  is the density of the sample and  is the density of water.

The apparent specific gravity is simply the ratio of the weights of equal volumes of sample and water in air:

where  represents the weight of sample and  the weight of water, both measured in air.

It can be shown that true specific gravity can be computed from different properties:

where  is the local acceleration due to gravity,  is the volume of the sample and of water (the same for both),  is the density of the sample,  is the density of water and  represents a weight obtained in vacuum.

The density of water varies with temperature and pressure as does the density of the sample so that it is necessary to specify the temperatures and pressures at which the densities or weights were determined. It is nearly always the case that measurements are made at nominally 1 atmosphere (1013.25 mbar ± the variations caused by changing weather patterns) but as specific gravity usually refers to highly incompressible aqueous solutions or other incompressible substances (such as petroleum products) variations in density caused by pressure are usually neglected at least where apparent specific gravity is being measured. For true (in vacuo) specific gravity calculations air pressure must be considered (see below). Temperatures are specified by the notation  with  representing the temperature at which the sample's density was determined and  the temperature at which the reference (water) density is specified. For example SG (20°C/4°C) would be understood to mean that the density of the sample was determined at 20 °C and of the water at 4°C. Taking into account different sample and reference temperatures we note that while  (20°C/20°C) it is also the case that  (20°C/4°C). Here temperature is being specified using the current ITS-90 scale and the densities^[2] used here and in the rest of this article are based on that scale. On the previous IPTS-68 scale the densities at 20 °C and 4 °C are, respectively, 0.9982071 and 0.9999720 resulting in an SG (20°C/4°C) value for water of 0.9982343.

As the principal use of specific gravity measurements in industry is determination of the concentrations of substances in aqueous solutions and these are found in tables of SG vs concentration it is extremely important that the analyst enter the table with the correct form of specific gravity. For example, in the brewing industry, the Plato table, which lists sucrose concentration by weight against true SG, were originally (20°C/4°C)^[3] i.e. based on measurements of the density of sucrose solutions made at laboratory temperature (20 °C) but referenced to the density of water at 4 °C which is very close to the temperature at which water has its maximum density of  equal to 0.999972 g·cm⁻³ in SI units (or 62.43 lb_m·ft⁻³ in United States customary units). The ASBC table^[4] in use today in North America, while it is derived from the original Plato table is for apparent specific gravity measurements at (20°C/20°C) on the IPTS-68 scale where the density of water is 0.9982071 g·cm⁻³. In the sugar, soft drink, honey, fruit juice and related industries sucrose concentration by weight is taken from a table prepared by A. Brix which uses SG (17.5°C/17.5°C). As a final example, the British SG units are based on reference and sample temperatures of 60F and are thus (15.56°C/15.56°C).

Given the specific gravity of a substance, its actual density can be calculated by rearranging the above formula:

Occasionally a reference substance other than water is specified (for example, air), in which case specific gravity means density relative to that reference.

Hydrometer

A hydrometer is an instrument used to measure the specific gravity (or relative density) of liquids; that is, the ratio of the density of the liquid to the density of water.

A hydrometer is usually made of glass and consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float upright. The liquid to be tested is poured into a tall container, often a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. The point at which the surface of the liquid touches the stem of the hydrometer is noted. Hydrometers usually contain a scale inside the stem, so that the specific gravity can be read directly. A variety of scales exist, and are used depending on the context.

Hydrometers may be calibrated for different uses, such as a lactometer for measuring the density (creaminess) of milk, a saccharometer for measuring the density of sugar in a liquid, or an alcoholometer for measuring higher levels of alcohol in spirits.

Operation of the hydrometer is based on Archimedes' principle that a solid suspended in a fluid will be buoyed up by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid. Thus, the lower the density of the substance, the farther the hydrometer will sink. (See also Relative density and hydrometers.)

An early description of a hydrometer appears in a letter from Synesius of Cyrene to the Greek scholar Hypatia of Alexandria. In Synesius' fifteenth letter, he requests Hypatia to make a hydrometer for him. Hypatia is given credit for inventing the hydrometer (or hydroscope) sometime in the late 4th century or early 5th century.^[1]

The instrument in question is a cylindrical tube, which has the shape of a flute and is about the same size. It has notches in a perpendicular line, by means of which we are able to test the weight of the waters. A cone forms a lid at one of the extremities, closely fitted to the tube. The cone and the tube have one base only. This is called the baryllium. Whenever you place the tube in water, it remains erect. You can then count the notches at your ease, and in this way ascertain the weight of the water.^[2]

According to the Encyclopedia of the History of Arabic Science, it was used by Abū Rayhān al-Bīrūnī in the 11th century and described by Al-Khazini in the 12th century.^[3]

It later appeared again in the work of Jacques Alexandre César Charles in the 18th century.

Specialized hydrometers

Specialized hydrometers are frequently named for their use: a lactometer, for example, is a hydrometer designed especially for use with dairy products.

Lactometer

Lactometer is used to check purity of milk. The specific gravity of milk does not give a conclusive indication of its composition since milk contains a variety of substances that are either heavier or lighter than water. Additional tests for fat content are necessary to determine overall composition. The instrument is graduated into a hundred parts. Milk is poured in and allowed to stand until the cream has formed, then the depth of the cream deposit in degrees determines the quality of the milk. The device works on the principle of Archimede's principle that a solid suspended in a fluid will be buoyed up by a force equal to the weight of the fluid displaced. If the milk sample is pure, then the lactometer floats on it and if it is adulterated or impure, then the lactometer sinks.^{[citation needed]}

Alcohol meter

A alcoholometer testing beer immediately after brewing, before fermentation.

An alcoholmeter is a hydrometer which is used for determining the alcoholic strength of liquids. It is also known as a proof and Tralles hydrometer(named after Johann Georg Tralles, but commonly misspelled as traille and tralle). It only measures the density of the fluid. Certain assumptions are made to estimate the amount of alcohol present in the fluid. Alcoholometers have scales marked with volume percents of "potential alcohol", based on a pre-calculated specific gravity. A higher "potential alcohol" reading on this scale is caused by a greater specific gravity, assumed to be caused by the introduction of dissolved sugars. A reading is taken before and after fermentation and approximate alcohol content is determined by subtracting the post fermentation reading from the pre-fermentation reading.^[5]

Saccharometer

A saccharometer is a hydrometer used for determining the amount of sugar in a solution, invented by Thomas Thomson.^{[citation needed]} It is used primarily by winemakers and brewers,^[6] and it can also be used in making sorbets and ice-creams.^[7] The first brewers' saccharometer was constructed by Benjamin Martin (with distillation in mind) and initially used for brewing by James Baverstock Sr in 1770.^[8] Henry Thrale adopted its use and it was later popularized by John Richardson in 1784.^[9]

It consists of a large weighted glass bulb with a thin stem rising from the top with calibrated markings. The sugar level can be determined by reading the value where the surface of the liquid crosses the scale. It works by the principle of buoyancy. A solution with a higher sugar content is denser, causing the bulb to float higher. Less sugar results in a lower density and a lower floating bulb.

Thermohydrometer

A thermohydrometer is a hydrometer that has a thermometer enclosed in the float section. For measuring the density of petroleum products, like fuel oils, the specimen is usually heated in a temperature jacket with a thermometer placed behind it since density is dependent on temperature. Light oils are placed in cooling jackets, typically at 15 °C. Very light oils with many volatile components are measured in a variable volume container using a floating piston sampling device to minimize light end losses.

As a battery test it measures the temperature compensated specific gravity and electrolyte temperature.

Urinometer

A urinometer is a medical hydrometer designed for urinalysis. As urine's specific gravity is dictated by its ratio of solutes (wastes) to water, a urinometer makes it possible to quickly assess a patient's overall level of hydration.

Barkometer

A barkometer is calibrated to test the strength of tanning liquors used in tanning leather.^[10]

Battery hydrometer

The state of charge of a lead-acid battery can be estimated from the density of the sulfuric acid solution used as electrolyte. A hydrometer calibrated to read specific gravity relative to water at 60 degrees Fahrenheit is a standard tool for servicing automobile batteries. Tables are used to correct the reading to the standard temperature.

Antifreeze tester

Another automotive use of hydrometers is testing the quality of the antifreeze solution used for engine cooling. The degree of freeze protection can be related to the density (and so concentration) of the antifreeze; different types of antifreeze have different relations between measured density and freezing point.

Acidometer

Sometimes spelled acidimeter, an acidometer is a hydrometer used to measure the specific gravity of an acid.

History of beer

Ale is one of the oldest beverages humans have produced, dating back to at least the 5th millennium BC and recorded in the written history of Ancient Egypt and Mesopotamia. As almost any cereal containing certain sugars can undergo spontaneous fermentation due to wild yeasts in the air, it is possible that beer-like beverages were independently developed throughout the world soon after a tribe or culture had domesticated cereal. Chemical tests of ancient pottery jars reveal that beer was produced about 7,000 years ago in what is today Iran, and is one of the first-known biological engineering tasks to utilize the process of fermentation. In Mesopotamia, the oldest evidence of beer is believed to be a 6,000-year-old Sumerian tablet depicting people drinking a beverage through reed straws from a communal bowl. A 3900-year-old Sumerian poem honouring Ninkasi, the patron goddess of brewing, contains the oldest surviving beer recipe, describing the production of beer from barley via bread.

The invention of bread and/or beer has been argued to be responsible for humanity's ability to develop technology and build civilization.^[2][3][4]The earliest chemically confirmed barley beer to date was discovered at Godin Tepe in the central Zagros Mountains of Iran, where fragments of a jug, at least 5000 years old was found to be coated with beerstone, a by-product of the brewing process.^[5]

Beer may have been known in Neolithic Europe as far back as 5000 years ago,^[6] and was mainly brewed on a domestic scale.^[7]

Ale produced before the Industrial Revolution continued to be made and sold on a domestic scale, although by the 7th century AD beer was also being produced and sold by European monasteries. During the Industrial Revolution, the production of beer moved from artisanalmanufacture to industrial manufacture, and domestic manufacture ceased to be significant by the end of the 19th century.^[8] The development of hydrometers and thermometers changed brewing by allowing the brewer more control of the process, and greater knowledge of the results.

Today, the brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs toregional breweries.^[9] More than 133 billion liters (35 billion gallons) are sold per year—producing total global revenues of $294.5 billion (£147.7 billion) in 2006.

In ancient Mesopotamia, clay tablets indicate that brewing was a fairly well respected occupation during the time, and that the majority of brewers were probably women.^[11] Indeed, the brewer's craft was the only profession in Mesopotamia which derived social sanction and divine protection from female deities/goddesses, specifically: Ninkasi, who covered the production of beer, Siris, who was used in a metonymic way to refer to beer, and Siduri, who covered the enjoyment of beer.^[12] Mesopotamian brewing appears to have incorporated the usage of a twice-baked barley bread called bappir, which was exclusively used for brewing beer.^[13] It was discovered early that reusing the same container for fermenting the mash would produce more reliable results; brewers on the move carried their tubs with them.^[14]

The Ebla tablets, discovered in 1974 in Ebla, Syria, which date to 2500 BC, reveal that the city produced a range of beers, including one that appears to be named "Ebla" after the city.^[15] Early traces of beer and the brewing process have been found in ancient Babylonia as well. At the time, brewers were women as well, but also priestesses. Some types of beers were used especially in religious ceremonies. In 2100 BC, the Babylonian king Hammurabi included regulations governing tavern keepers in his law code for the kingdom.^[16]

A funerary model of a bakery and brewery, from the Eleventh dynasty of Egypt, circa 2009–1998 BC

Beer was part of the daily diet of Egyptian Pharaohs over 5,000 years ago. Then, it was made from baked barley bread, and was also used in religious practices.^[17]

The Greek writer Sophocles (450 BCE) discussed the concept of moderation when it came to consuming beer in Greek culture, and believed that the best diet for Greeks consisted of bread, meats, various types of vegetables, and beer or "ζῦθος" (zythos) as they called it.^[18] The ancient Greeks also made barleywine (Greek: "κρίθινος οἶνος" - krithinos oinos, "barley wine"^[19][20]) mentioned by Greek historian Polybius in his workThe Histories, where he states that Phaeacians kept barleywine in silver and golden kraters.^[21]

In Europe during the Middle Ages, a brewers' guild might adopt a patron saint of brewing. Arnulf of Metz (c. 582–640) and Arnulf of Oudenburg (c. 1040–1087) were recognized by some French and Flemish brewers.^[22] Belgian brewers, too, venerated Arnulf of Oudenburg (aka Arnold of Soissons),^[23] who is also recognized as the patron saint of hop-pickers. Christian monks built breweries, to provide food, drink, and shelter to travelers and pilgrims.^[17]

Charlemagne, Frankish king and ruler of the Holy Roman Empire during the 8th century, considered beer to be an important part of living, and is often thought to have trained some brewers himself.

As almost any cereal containing certain sugars can undergo spontaneous fermentation due to wild yeasts in the air, it is possible that beer-like beverages were independently developed throughout the world soon after a tribe or culture had domesticated cereal. Chemical tests of ancient pottery jars reveal that beer was produced about 3,500 BC in what is today Iran, and was one of the first-known biological engineering tasks where the biological process of fermentation is used. Also recent archaeological findings showing that Chinese villagers were brewing fermented alcoholic drinks as far back as 7000 BC on small and individual scale, with the production process and methods similar to that of ancient Egypt and Mesopotamia.^[24]

In Mesopotamia (Ancient Iraq), early evidence of beer is a 3900-year-old Sumerian poem honoring Ninkasi, the patron goddess of brewing, which contains the oldest surviving beer recipe, describing the production of beer from barley via bread.^[25]

Ninkasi, you are the one who pours out the filtered beer of the collector vat

It is [like] the onrush of Tigris and Euphrates.^[26]

Beer is also mentioned in the Epic of Gilgamesh, in which the 'wild man' Enkidu is given beer to drink. "... he ate until he was full, drank seven pitchers of beer, his heart grew light, his face glowed and he sang out with joy."

Confirmed written evidence of ancient beer production in Armenia can be obtained from Xenophon in his work Anabasis (5th century B.C.) when he was in one of the ancient Armenian villages in which he wrote:

“

There were stores within of wheat and barley and vegetables, and wine made from barley in great big bowls; the grains of barley malt lay floating in the beverage up to the lip of the vessel, and reeds lay in them, some longer, some shorter, without joints; when you were thirsty you must take one of these into your mouth, and suck. The beverage without admixture of water was very strong, and of a delicious flavour to certain palates, but the taste must be acquired.[27][28]

”

Beer became vital to all the grain-growing civilizations of Eurasian and North African antiquity, including Egypt—so much so that in 1868 James Death put forward a theory in The Beer of the Bible that the manna from heaven that God gave the Israelites was a bread-based, porridge-like beer called wusa.

These beers were often thick, more of a gruel than a beverage, and drinking straws were used by the Sumerians to avoid the bitter solids left over from fermentation. Though beer was drunk in Ancient Rome, it was replaced in popularity by wine.^[29] Tacitus wrote disparagingly of the beer brewed by the Germanic peoples of his day. Thracians were also known to consume beer made from rye, even since the 5th century BC, as Hellanicus of Lesbos says. Their name for beer was brutos, or brytos. The Romans called their brewcerevisia, from the Celtic word for it.

Ancient Nubians had used beer as an antibiotic medicine

Beer

Beer is an alcoholic beverage produced by the saccharification of starch and fermentation of the resulting sugar. The starch and saccharification enzymes are often derived from malted cereal grains, most commonly malted barley and malted wheat.[1] Most beer is also flavoured with hops, which add bitterness and act as a natural preservative, though other flavourings such as herbs or fruit may occasionally be included. The preparation of beer is called brewing. Beer is the world's most widely consumed alcoholic beverage,[2] and is the third-most popular drink overall, after water and tea.[3] It is thought by some to be the oldest fermented beverage.[4][5][6][7] Some of humanity's earliest known writings refer to the production and distribution of beer: the Code of Hammurabi included laws regulating beer and beer parlours,[8] and "The Hymn to Ninkasi", a prayer to the Mesopotamian goddess of beer, served as both a prayer and as a method of remembering the recipe for beer in a culture with few literate people.[9][10] Today, the brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries. The strength of beer is usually around 4% to 6% alcohol by volume (abv) although it may vary between 0.5% (de-alcoholized) and 20%, with some breweries creating examples of 40% abv and above in recent years. Beer forms part of the culture of beer-drinking nations and is associated with social traditions such as beer festivals, as well as a rich pub culture involving activities like pub crawling and pub games such as bar billiards.

History

Egyptian wooden model of beer making in ancient Egypt, Rosicrucian Egyptian Museum, San Jose, California

Beer is one of the world's oldest prepared beverages, possibly dating back to the early Neolithic or 9500 BC, when cereal was firstfarmed,^[11] and is recorded in the written history of ancient Iraq and ancient Egypt.^[12] Archaeologists speculate that beer was instrumental in the formation of civilisations.^[13]

The earliest known chemical evidence of barley beer dates to circa 3500–3100 BC from the site of Godin Tepe in the Zagros Mountains of western Iran.^[14][15] Some of the earliest Sumerian writings contain references to beer; examples include a prayer to the goddess Ninkasi, known as "The Hymn to Ninkasi",^[16] which served as both a prayer as well as a method of remembering the recipe for beer in a culture with few literate people,^[9][10] and the ancient advice (Fill your belly. Day and night make merry) to Gilgamesh, recorded in the Epic of Gilgamesh, by the ale-wife Siduri may, at least in part, have referred to the consumption of beer.^[17] The Ebla tablets, discovered in 1974 in Ebla, Syria and date back to 2500 BC, reveal that the city produced a range of beers, including one that appears to be named "Ebla" after the city.^[18] A fermented beverage using rice and fruit was made in China around 7000 BC. Unlike sake, mold was not used to saccharify the rice (amylolytic fermentation); the rice was probably prepared for fermentation by mastication or malting,^[19][20]

Almost any substance containing sugar can naturally undergo alcoholic fermentation. It is likely that many cultures, on observing that a sweet liquid could be obtained from a source of starch, independently invented beer. Bread and beer increased prosperity to a level that allowed time for development of other technologies and contributed to the building of civilizations.^{[21][22][23][24]}

Beer was spread through Europe by Germanic and Celtic tribes as far back as 3000 BC,^[25] and it was mainly brewed on a domestic scale.^[26] The product that the early Europeans drank might not be recognised as beer by most people today. Alongside the basic starch source, the early European beers might contain fruits, honey, numerous types of plants, spices and other substances such as narcotic herbs.^[27] What they did not contain was hops, as that was a later addition, first mentioned in Europe around 822 by a Carolingian Abbot^[28] and again in 1067 by Abbess Hildegard of Bingen.^[29]

At the Café by Édouard Manet

In 1516, William IV, Duke of Bavaria, adopted the Reinheitsgebot (purity law), perhaps the oldest food-quality regulation still in use in the 21st century, according to which the only allowed ingredients of beer are water, hops and barley-malt.^[30] Beer produced before theIndustrial Revolution continued to be made and sold on a domestic scale, although by the 7th century AD, beer was also being produced and sold by European monasteries. During the Industrial Revolution, the production of beer moved from artisanal manufacture to industrial manufacture, and domestic manufacture ceased to be significant by the end of the 19th century.^[31] The development of hydrometers andthermometers changed brewing by allowing the brewer more control of the process and greater knowledge of the results.

Today, the brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries.^[32] As of 2006, more than 133 billion liters (35 billion gallons), the equivalent of a cube 510 metres on a side, of beer are sold per year, producing total global revenues of $294.5 billion (£147.7 billion).^[33]

In 2010, China's beer consumption hit 450 million hectoliters (45 billion liters) or nearly twice that of the United States but only 5 percent sold were Premium draught beers, compared with 50 percent in France and Germany.^[34]

Brewing

Main article: Brewing

A 16th-century brewery

The process of making beer is known as brewing. A dedicated building for the making of beer is called a brewery, though beer can be made in the home and has been for much of its history. A company that makes beer is called either a brewery or a brewing company. Beer made on a domestic scale for non-commercial reasons is classified as homebrewing regardless of where it is made, though most homebrewed beer is made in the home. Brewing beer is subject to legislation and taxation in developed countries, which from the late 19th century largely restricted brewing to a commercial operation only. However, the UK government relaxed legislation in 1963, followed by Australia in 1972 and the USA in 1978, allowing homebrewing to become a popular hobby.^[35]

The purpose of brewing is to convert the starch source into a sugary liquid called wort and to convert the wort into the alcoholic beverage known as beer in a fermentation process effected by yeast.

Diagram illustrating the process of brewing beer

Hot Water Tank

Mash Tun

Malt

Hops

Copper

Hopback

Add Yeast to
Fermenter

Heat
exchanger

Bottling

Cask or Keg

The first step, where the wort is prepared by mixing the starch source (normally malted barley) with hot water, is known as "mashing". Hot water (known as "liquor" in brewing terms) is mixed with crushed malt or malts (known as "grist") in a mash tun.^[36] The mashing process takes around 1 to 2 hours,^[37] during which the starches are converted to sugars, and then the sweet wort is drained off the grains. The grains are now washed in a process known as "sparging". This washing allows the brewer to gather as much of the fermentable liquid from the grains as possible. The process of filtering the spent grain from the wort and sparge water is called wort separation. The traditional process for wort separation is lautering, in which the grain bed itself serves as the filter medium. Some modern breweries prefer the use of filter frames which allow a more finely ground grist.^[38]

Most modern breweries use a continuous sparge, collecting the original wort and the sparge water together. However, it is possible to collect a second or even third wash with the not quite spent grains as separate batches. Each run would produce a weaker wort and thus a weaker beer. This process is known as second (and third) runnings. Brewing with several runnings is called parti gyle brewing.^[39]

The sweet wort collected from sparging is put into a kettle, or "copper", (so called because these vessels were traditionally made from copper)^[40] and boiled, usually for about one hour. During boiling, water in the wort evaporates, but the sugars and other components of the wort remain; this allows more efficient use of the starch sources in the beer. Boiling also destroys any remaining enzymes left over from the mashing stage. Hops are added during boiling as a source of bitterness, flavour and aroma. Hops may be added at more than one point during the boil. The longer the hops are boiled, the more bitterness they contribute, but the less hop flavour and aroma remains in the beer.^[41]

After boiling, the hopped wort is now cooled, ready for the yeast. In some breweries, the hopped wort may pass through a hopback, which is a small vat filled with hops, to add aromatic hop flavouring and to act as a filter; but usually the hopped wort is simply cooled for the fermenter, where the yeast is added. During fermentation, the wort becomes beer in a process which requires a week to months depending on the type of yeast and strength of the beer. In addition to producing alcohol, fine particulate matter suspended in the wort settles during fermentation. Once fermentation is complete, the yeast also settles, leaving the beer clear.^[42]

Fermentation is sometimes carried out in two stages, primary and secondary. Once most of the alcohol has been produced during primary fermentation, the beer is transferred to a new vessel and allowed a period of secondary fermentation. Secondary fermentation is used when the beer requires long storage before packaging or greater clarity.^[43] When the beer has fermented, it is packaged either into casks for cask ale or kegs, aluminium cans, or bottles for other sorts of beer.^[44]

Ingredients

Malted barley before roasting

The basic ingredients of beer are water; a starch source, such as malted barley, able to be saccharified (converted to sugars) then fermented (converted into alcohol and carbon dioxide); a brewer's yeast to produce the fermentation; and a flavouring such as hops.^[45] A mixture of starch sources may be used, with a secondary starch source, such as maize (corn), rice or sugar, often being termed anadjunct, especially when used as a lower-cost substitute for malted barley.^[46] Less widely used starch sources include millet, sorghumand cassava root in Africa, and potato in Brazil, and agave in Mexico, among others.^[47] The amount of each starch source in a beer recipe is collectively called the grain bill.

Water

Beer is composed mostly of water. Regions have water with different mineral components; as a result, different regions were originally better suited to making certain types of beer, thus giving them a regional character.^[48] For example, Dublin has hard water well-suited to making stout, such as Guinness; while the Plzeň Region has soft water well-suited to making Pilsner (pale lager), such as Pilsner Urquell.^[48] The waters of Burton in England contain gypsum, which benefits making pale ale to such a degree that brewers of pale ales will add gypsum to the local water in a process known as Burtonisation.^[49]

Starch source

Main articles: Malt and Mash ingredients

The starch source in a beer provides the fermentable material and is a key determinant of the strength and flavour of the beer. The most common starch source used in beer is malted grain. Grain is malted by soaking it in water, allowing it to begin germination, and then drying the partially germinated grain in a kiln. Malting grain produces enzymes that convert starches in the grain into fermentable sugars.^[50] Different roasting times and temperatures are used to produce different colours of malt from the same grain. Darker malts will produce darker beers.^[51]

Nearly all beer includes barley malt as the majority of the starch. This is because its fibrous hull remains attached to the grain during threshing. After malting, barley is milled, which finally removes the hull, breaking it into large pieces. These pieces remain with the grain during the mash, and act as a filter bed during lautering, when sweet wort is separated from insoluble grain material. Other malted and unmalted grains (including wheat, rice, oats, and rye, and less frequently, corn and sorghum) may be used. In recent years, a few brewers have produced gluten-free beer, made with sorghum with no barley malt, for those who cannot consume gluten-containing grains like wheat, barley, and rye.^[52]

Hops

Main article: Hops

Hop cone in a Hallertau, Germany, hop yard

Flavouring beer is the sole major commercial use of hops.^[53] The flower of the hop bine is used as a flavouring and preservative agent in nearly all beer made today. The flowers themselves are often called "hops".

The first historical mention of the use of hops in beer was from 822 AD in monastery rules written by Adalhard the Elder, also known asAdalard of Corbie,^[31][54] though the date normally given for widespread cultivation of hops for use in beer is the thirteenth century.^[31][54]Before the thirteenth century, and until the sixteenth century, during which hops took over as the dominant flavouring, beer was flavoured with other plants; for instance, Glechoma hederacea. Combinations of various aromatic herbs, berries, and even ingredients likewormwood would be combined into a mixture known as gruit and used as hops are now used.^[55] Some beers today, such as Fraoch' by the Scottish Heather Ales company^[56] and Cervoise Lancelot by the French Brasserie-Lancelot company,^[57] use plants other than hops for flavouring.

Hops contain several characteristics that brewers desire in beer. Hops contribute a bitterness that balances the sweetness of the malt; the bitterness of beers is measured on the International Bitterness Units scale. Hops contribute floral, citrus, and herbal aromas and flavours to beer. Hops have an antibiotic effect that favours the activity of brewer's yeast over less desirable microorganisms and aids in "head retention",^[58][59] the length of time that a foamy head created by carbonation will last. The acidity of hops is a preservative.^[60][61]

Yeast

Main articles: Brewer's yeast, Saccharomyces cerevisiae, and Saccharomyces uvarum

Yeast is the microorganism that is responsible for fermentation in beer. Yeast metabolises the sugars extracted from grains, which produces alcohol and carbon dioxide, and thereby turns wort into beer. In addition to fermenting the beer, yeast influences the character and flavour.^[62]

The dominant types of yeast used to make beer are the top-fermenting Saccharomyces cerevisiae and bottom-fermenting Saccharomyces uvarum.^[63] Brettanomyces fermentslambics,^[64] and Torulaspora delbrueckii ferments Bavarian weissbier.^[65]

Before the role of yeast in fermentation was understood, fermentation involved wild or airborne yeasts. A few styles such as lambics rely on this method today, but most modern fermentation adds pure yeast cultures.^[66]

Clarifying agent

Some brewers add one or more clarifying agents to beer, which typically precipitate (collect as a solid) out of the beer along with protein solids and are found only in trace amounts in the finished product. This process makes the beer appear bright and clean, rather than the cloudy appearance of ethnic and older styles of beer such as wheat beers.^[67]

Examples of clarifying agents include isinglass, obtained from swimbladders of fish; Irish moss, a seaweed; kappa carrageenan, from the seaweed Kappaphycus cottonii; Polyclar(artificial); and gelatin.^[68] If a beer is marked "suitable for Vegans", it was clarified either with seaweed or with artificial agents.^[69]

Production and trade

Beer Consumption by Country

Banner of a Microbrewery in the Franconian Switzerland, Germany

The Benedictine Weihenstephan Brewery in Bavaria, Germany, can trace its roots to the year 768, as a document from that year refers to a hop garden in the area paying a tithe to the monastery. The brewery was licensed by the City of Freising in 1040, and therefore is the oldest working brewery in the world.^[70] The oldest brewery with discontinuous production is the Břevnov Monastery in the Czech Republic, which was founded in 993.

The brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries.^[32] More than 133 billion liters (35 billion gallons) are sold per year—producing total global revenues of $294.5 billion (£147.7 billion) as of 2006.^[33]

A microbrewery, or craft brewery, is a modern brewery which produces a limited amount of beer. The maximum amount of beer a brewery can produce and still be classed as a microbrewery varies by region and by authority, though is usually around 15,000 barrels (1.8 megalitres, 396 thousand imperial gallons or 475 thousand US gallons) a year.^[71] A brewpub is a type of microbrewery that incorporates a pub or other eating establishment.

The highest density of breweries in the world, most of them microbreweries, exists in the German Region ofFranconia, especially in the district of Upper Franconia, which has about 200 breweries.^[72][73]

SABMiller became the largest brewing company in the world when it acquired Royal Grolsch, brewer of Dutch premium beer brand Grolsch.^[74] InBev was the second-largest beer-producing company in the world andAnheuser-Busch held the third spot, but after the acquisition of Anheuser-Busch by InBev, the new Anheuser-Busch InBev company is currently the largest brewer in the world.^[75]

Brewing at home is subject to regulation and prohibition in many countries. Restrictions on homebrewing were lifted in the UK in 1963,^[76] Australia followed suit in 1972,^[77] and the USA in 1978, though individual states were allowed to pass their own laws limiting production.^[78]

Beer Imports by Nation. From MIT/Harvard MIT/Harvard Atlas of Economic Complexity

Beer Exports by Nation. From MIT/Harvard MIT/Harvard Atlas of Economic Complexity

Varieties

Cropton, a typical UK microbrewery

25 litres of homebrew

Kriek, a variety of beer brewed with cherries

While there are many types of beer brewed, the basics of brewing beer are shared across national and cultural boundaries.^[79] The traditional European brewing regions—Germany, Belgium, England and the Czech Republic—have local varieties of beer.^[80]

English writer Michael Jackson, in his 1977 book The World Guide To Beer, categorised beers from around the world in local style groups suggested by local customs and names.^[81] Fred Eckhardt furthered Jackson's work in The Essentials of Beer Style in 1989.

Cask ale hand pumps with pump clips detailing the beers and their breweries

Top-fermented beers are most commonly produced with Saccharomyces cerevisiae, a top-fermenting yeast which clumps and rises to the surface,^[82] typically between 15 and 24 °C (60 and 75 °F). At these temperatures, yeast produces significant amounts of esters and other secondary flavour and aroma products, and the result is often a beer with slightly "fruity" compounds resembling apple, pear, pineapple, banana, plum, or prune, among others.^[83]

Before the introduction of hops into England from the Netherlands in the 15th century, the names "ale" and "beer" were exclusively applied to unhopped fermented beverages, the term beer being gradually shifted to describe a brew with an infusion of hops.^[84]

The word ale comes from Old English ealu (plural ealoþ), in turn from Proto-Germanic *alu (plural *aluþ), ultimately from the Proto-Indo-European base *h₂elut-, which holds connotations of "sorcery, magic, possession, intoxication".^[85][86][87] The word beer comes from Old Englishbēor, from Proto-Germanic *beuzą, probably from Proto-Indo-European *bʰeusóm, originally "brewer's yeast, beer dregs", although other theories have been provided connecting the word with Old English bēow, "barley", or Latin bibere, "to drink".^[88][89] On the currency of two words for the same thing in the Germanic languages, the 12th-century Old Icelandic poem Alvíssmál says, "Ale it is called among men, but among the gods, beer."^[90]

Real ale is the term coined by the Campaign for Real Ale (CAMRA) in 1973^[91] for "beer brewed from traditional ingredients, matured bysecondary fermentation in the container from which it is dispensed, and served without the use of extraneous carbon dioxide". It is applied tobottle conditioned and cask conditioned beers.

Pale Ale

Pale ale is a beer which uses a top-fermenting yeast^[92] and predominantly pale malt. It is one of the world's major beer styles.

Stout

Stout and porter are dark beers made using roasted malts or roast barley, and typically brewed with slow fermenting yeast. There are a number of variations including Baltic porter, dry stout, and Imperial stout. The name Porter was first used in 1721 to describe a dark brown beer popular with the street and river porters of London.^[93] This same beer later also became known as stout, though the word stout had been used as early as 1677.^[94] The history and development of stout and porter are intertwined.^[95]

Mild

Mild ale has a predominantly malty palate. It is usually dark coloured with an abv of 3% to 3.6%, although there are lighter hued milds as well as stronger examples reaching 6% abv and higher.

Wheat

Wheat beer is brewed with a large proportion of wheat although it often also contains a significant proportion of malted barley. Wheat beers are usually top-fermented (in Germany they have to be by law).^[96] The flavour of wheat beers varies considerably, depending upon the specific style.

Lager

Lager is the English name for cool fermenting beers of Central European origin. Pale lagers are the most commonly consumed beers in the world. The name "lager" comes from the German "lagern" for "to store", as brewers around Bavaria stored beer in cool cellars and caves during the warm summer months. These brewers noticed that the beers continued to ferment, and to also clear of sediment, when stored in cool conditions.^[97]

Lager yeast is a cool bottom-fermenting yeast (Saccharomyces pastorianus) and typically undergoes primary fermentation at 7–12 °C (45–54 °F) (the fermentation phase), and then is given a long secondary fermentation at 0–4 °C (32–39 °F) (the lagering phase). During the secondary stage, the lager clears and mellows. The cooler conditions also inhibit the natural production of esters and other byproducts, resulting in a "cleaner"-tasting beer.^[98]

Modern methods of producing lager were pioneered by Gabriel Sedlmayr the Younger, who perfected dark brown lagers at the Spaten Brewery in Bavaria, and Anton Dreher, who began brewing a lager (now known as Vienna lager), probably of amber-red colour, in Vienna in 1840–1841. With improved modern yeast strains, most lager breweries use only short periods of cold storage, typically 1–3 weeks.

Lambic

Lambic, a beer of Belgium, is naturally fermented using wild yeasts, rather than cultivated. Many of these are not strains of brewer's yeast (Saccharomyces cerevisiae) and may have significant differences in aroma and sourness. Yeast varieties such as Brettanomyces bruxellensis and Brettanomyces lambicus are common in lambics. In addition, other organisms such as Lactobacillus bacteria produce acids which contribute to the sourness.^[99]