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How Chemistry Affects Beer Taste

How Chemistry Affects Beer Taste. Matt Kade Chem 290 5/15/08. Some beer history. Evidence that beer has been made since 6000 B.C. Reinheitsgebot (German purity law) of 1487 Barley, hops and water ONLY Pasteur discovers yeast (1857). Beer Styles. Alcohol content Residual sugars

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How Chemistry Affects Beer Taste

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  1. How Chemistry Affects Beer Taste Matt Kade Chem 290 5/15/08

  2. Some beer history • Evidence that beer has been made since 6000 B.C. • Reinheitsgebot (German purity law) of 1487 • Barley, hops and water ONLY • Pasteur discovers yeast (1857)

  3. Beer Styles • Alcohol content • Residual sugars • Hop bitterness • Adjuncts used • Other products of fermentation

  4. Overview of Process • malting • fermentation • bottling and ageing • boiling • mashing

  5. Malting • Barley is incubated to open hull, start conversion of starches • Heated to 60°C to dry malt, stop process, • Dry to less than 4% water content

  6. Kilning 75°C 110°C Czech Pilsener Pale Ale Amber Malt Brown Malt vs.

  7. Maillard Reaction • Discovered by Louis Camille Maillard in 1913 • Essential in cooked food (e.g. seared meat, bakery products, roasted coffee) • Reactions between ‘reducing sugar’ and amino acid • Produces thousands of potential flavor and color compounds

  8. Maillard Reaction N-glucosylamine (Amadori complex) • Five main reducing sugars * 20 amino acids = 100 possible Amadori products

  9. Maillard Products Biscuit-like Cooked rice Sharp toasted, burnt Sweet corn

  10. Mashing • Break down carbohydrates into fermentable sugars • Break down proteins into usable amino acids • Choose temperature range where different enzymes are highly active for various processes • Amylases (α and β) can only break down 1,4 linkages Maltose: 1,4 linkage Isomaltose: 1,6 linkage Laminaribiose: 1,3 linkage

  11. Mashing schedule α amylase β amylase proteases peptidases Beta Glucanase Temperature oC Time / minutes

  12. The Boil • Sanitizes wort • Remove volatile products (e.g. dimethyl sulfide) • Additional Maillard reactions occur • Hop chemistry

  13. Hops α- acids • Balance residual sweetness • Provide aroma • Preservative properties • Major components: • Alpha acids • (Sesqui)terpenes • Hetero-atom containing hydrocarbons humulene linalool

  14. Alpha Acid Isomerization humulone isohumulone

  15. Hop addition schedule • For a typical one hour boil: • Add hops at start • Add hops with <5 minutes left • Sometimes add hops after boil during fermentation • Aroma-providing hydrocarbons are volatile! humulene myrcene farnesene caryophyllene

  16. Fermentation • Uses single strand of yeast • Follows Emden-Meyerhoff-Parnas pathway (glycolysis) ending in ethanol • Must Avoid bacterial / wild yeast infection • Requires steady temperature

  17. Yeast • Discovered by Louis Pasteur • Saccharomycescerevisiae (ale) • Saccharomycescarsbergenis (lager) • Typically ‘pitch’ 15-20 million yeast cells per mL of wort

  18. EMP Pathway ATP ADP Phosphoglucoseisomerase Hexokinase ATP ADP Phosphofructokinase + Fructose bisphosphatealdolase

  19. Glycolysis Glyceraldehyde phosphate dehydrogenase NAD+ NADH Triosephosphateisomerase NAD+ NADH ADP ATP ADP ATP Phosphoglyceratekinase H2O Phosphoglyceratemutase H2O Enolase

  20. Formation of Ethanol ADP ATP CO2 NADH NAD+ Pyruvate kinase • Typical concentrations of ethanol formed: 40 to 60 g/L

  21. Strickland Reaction • Amino acid pool determines fusel alcohols present in fermenting beer

  22. Fusel Alcohols in Beer

  23. Important Ketones in Beer

  24. Esters in Beer

  25. Budweiser vs. Coors How do professional tasters distinguish between: : apple : pineapple

  26. Bottling • Cask or bottle conditioned (natural) • Force carbonate • Allow to age in bottle

  27. Ageing • Goaty and cheesy flavors • Ageing can induce haze formation from proteins or tannins: • Silica gels • Sols Poly(vinylpyrrolidone)

  28. Skunky Beer

  29. Flavor Wheel

  30. Conclusions • A good beer requires: • Quality malt • Good choice of kilned or roasted malt • Effective use of hops or other adjuncts • Healthy fermentation • Right amount of other products (esters, etc.) • Effective storage

  31. References • Fix, George. Principles of Brewing Science, 1999. • Janson, Lee W., Brew Chem 101, 1996. • Palmer, John, How to Brew, 2006. • http://www.wikipedia.com • Lehninger, et al, Principles of Biochemistry, 2006 • Heath, B, Flavor Chemistry and technology, 1988. • Ingledew, W.M., J. Am. Soc. Brew. Chem., 37, 1979 • Peacock, V.E. et al, J. Agric. Food Chem, 29, 1981 • Papazian, Charlie, Microbrewed Adventures, 2005 • Mosher, Randy, Radical Brewing, 2004

  32. Acknowledgements • Dan Burke, Eric Pressly, Katie Feldman, Nalini Gupta, Neil Treat, Jasmine Hunt • James Pavlovich • Louis Pasteur • Louis Maillard • Charlie Papazian (founder of American Homebrewers Association and the Great American Beer Festival)

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