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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
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
Czech
Pilsener
110°C
Pale
Ale
Amber
Malt
vs.
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
T
e
m
p
e
r
a
t
u
r
e
o
C
80
α amylase
70
β amylase
60
proteases
50
peptidases
Beta
Glucanase
40
30
20
10
0
0
20
40
60
Time / minutes
80
100
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
α- acids
humulene
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
humulene
myrcene
farnesene
caryophyllene
Aroma-providing
hydrocarbons are volatile!
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
Hexokinase
Phosphoglucose
isomerase
ATP
Phosphofructokinase
+
Fructose
bisphosphate
aldolase
ADP
Glycolysis
Glyceraldehyde
phosphate
dehydrogenase
NAD+ NADH
Triosephosphate
isomerase
NAD+ NADH
Phosphoglycerate
kinase
ADP
ADP
ATP
ATP
H2O
H2O
Enolase
Phosphoglycerate
mutase
Formation of Ethanol
ADP
ATP
CO2
NADH
Pyruvate
kinase
• Typical concentrations of ethanol formed: 40 to 60 g/L
NAD+
Strickland Reaction
• Amino acid pool determines fusel alcohols present in fermenting beer
Fusel Alcohols in Beer
Name
Structure
Range
(mg/L)
Threshold Flavor
(mg/L)
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 Beer
Name
Structure
Range
(mg/L)
Threshold Flavor
(mg/L)
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:
• Silica gels
• Sols
Poly(vinylpyrrolidone)
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)