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

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

• mal

ting

• m

ashi

ng• b

oilin

g• f

erm

enta

tion

• bot

tling

and

age

ing

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

10

20

30

40

50

60

70

80Temperature 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 Pathway

ATP ADP

ATP

ADP

+

HexokinasePhosphoglucose isomerase

Phosphofructokinase

Fructose bisphosphate aldolase

Glycolysis

NAD+ NADH

NAD+ NADH

ADP

ATP

ADP

ATP

H2O

H2O

Triosephosphate isomerase

Glyceraldehyde phosphate dehydrogenase

Phosphoglycerate kinase

Phosphoglycerate mutase

Enolase

Formation of Ethanol

ADP 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. 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, 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)