Download Chemistry of beer

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)