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 mashing boiling fermentation bottling and ageing

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 vs. Czech Pilsener Pale Ale Amber Malt Brown Malt

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 Temperature oCTemperature oC Time / minutes Beta Glucanase β amylase α amylase peptidases proteases

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

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

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 Saccharomyces cerevisiae (ale) Saccharomyces carsbergenis (lager) Typically ‘pitch’ 15-20 million yeast cells per mL of wort

18. EMP Pathway ATP ADP ATP ADP + Hexokinase Phosphoglucose isomerase Phosphofructokinase Fructose bisphosphate aldolase

19. Glycolysis NAD + NADH ADP ATP ADP ATP H2OH2O H2OH2O Triosephosphate isomerase Glyceraldehyde phosphate dehydrogenase Phosphoglycerate kinase Phosphoglycerate mutase Enolase

20. Formation of Ethanol ADP ATP CO 2 NADH NAD + Typical concentrations of ethanol formed: 40 to 60 g/L Pyruvate kinase

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

22. Fusel Alcohols in Beer NameStructureRange (mg/L) Threshold (mg/L) Flavor Propanol10 - 40600 - 800Alcohol, rough Butanol5 - 60160 - 200Alcohol, rough Isobutanol10 - 60180 - 200Alcohol, rough 3-methylbutanol100 - 11040 - 130Alcohol, banana Isoamyl alcohol100 - 11040 - 130Alcohol, banana 2-phenylethanol100 - 20010 - 80Roses, bitter, chem 4-ethylphenol100 - 20010 - 80Roses, bitter, chem

23. Important Ketones in Beer NameStructureThreshold (mg/L) Taste Diacetyl0.1-0.5Buttery α -acetolactic acid_Sour Acetoin1.0Fruity, musty 2,3-pentanedione1.0Honey α -acetoxyhydroxy butyric acid 1.0Rubber

24. Esters in Beer NameStructureRange (mg/L) Threshold (mg/L) Flavor Ethyl acetate 15-20 (up to 40 in English ales) 33Fruity with solvent undertone Isoamyl acetate 1.5 – 2.5 (up to 6 in Belg/English) 3Bananas Ethyl hexanoate Widely varying 123Apples

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: Poly(vinylpyrrolidone) Silica gels Sols

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)