how chemistry affects beer taste

How Chemistry Affects Beer Taste

Matt KadeChem 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• m

alting

• mashin

g• b

oiling

• ferm

entat

ion

• bott

ling a

nd ag

eing

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

Kilning75°C 110°C

vs.

CzechPilsener

PaleAle

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

0 10 20 30 40 50 60 70 80 900

1020304050607080T

emperature o

C

Time / minutes

Beta Glucanase

β amylase

α amylase

peptidasesproteases

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!

humulene myrcene

farnesene caryophyllene

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’ 15-20 million

yeast cells per mL of wort

EMP PathwayATP ADP

ATP

ADP

+

Hexokinase Phosphoglucose isomerase

Phosphofructokinase

Fructose bisphosphate aldolase

GlycolysisNAD+ NADH

NAD+ NADH

ADP

ATP

ADP

ATP

H2O

H2O

Triosephosphate isomerase

Glyceraldehyde phosphate dehydrogenase

Phosphoglycerate kinase

Phosphoglycerate mutase

Enolase

Formation of EthanolADP ATP CO2 NADH NAD+

• Typical concentrations of ethanol formed: 40 to 60 g/L

Pyruvatekinase

Strickland Reaction

• Amino acid pool determines fusel alcohols present in fermenting beer

Fusel Alcohols in BeerName Structure Range

(mg/L)Threshold(mg/L)

Flavor

Propanol 10 - 40 600 - 800

Alcohol, rough

Butanol 5 - 60 160 - 200

Alcohol, rough

Isobutanol 10 - 60 180 - 200

Alcohol, rough

3-methylbutanol

100 - 110 40 - 130 Alcohol, banana

Isoamyl alcohol

100 - 110 40 - 130 Alcohol, banana

2-phenylethanol

100 - 200 10 - 80 Roses, bitter, chem

4-ethylphenol 100 - 200 10 - 80 Roses, bitter, chem

Important Ketones in Beer

Name Structure Threshold(mg/L)

Taste

Diacetyl 0.1-0.5 Buttery

α-acetolactic acid

_ Sour

Acetoin 1.0 Fruity, musty

2,3-pentanedione

1.0 Honey

α-acetoxyhydroxy butyric acid

1.0 Rubber

Esters in BeerName Structure Range

(mg/L)Threshold(mg/L)

Flavor

Ethyl acetate

15-20(up to 40 in English ales)

33 Fruity with solvent undertone

Isoamyl acetate

1.5 – 2.5 (up to 6 in Belg/English)

3 Bananas

Ethyl hexanoate

Widely varying

123 Apples

Budweiser vs. CoorsHow 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, 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

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)