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)