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 Hop bitterness Adjuncts used Other products of fermentation

Overview of Process malting mashing boiling fermentation bottling and ageing

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

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

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

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

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

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

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

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

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

Alpha Acid Isomerization humulone isohumulone

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

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

Yeast Discovered by Louis Pasteur Saccharomyces cerevisiae (ale) Saccharomyces carsbergenis (lager) Typically ‘pitch’ million yeast cells per mL of wort

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

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

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

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

Fusel Alcohols in Beer NameStructureRange (mg/L) Threshold (mg/L) Flavor Propanol Alcohol, rough Butanol Alcohol, rough Isobutanol Alcohol, rough 3-methylbutanol Alcohol, banana Isoamyl alcohol Alcohol, banana 2-phenylethanol Roses, bitter, chem 4-ethylphenol Roses, bitter, chem

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

Esters in Beer NameStructureRange (mg/L) Threshold (mg/L) Flavor Ethyl acetate (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

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

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

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

Skunky Beer

Flavor Wheel

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

References Fix, George. Principles of Brewing Science, Janson, Lee W., Brew Chem 101, Palmer, John, How to Brew, Lehninger, et al, Principles of Biochemistry, 2006 Heath, B, Flavor Chemistry and technology, 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

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)