Some Comments from a Chemist
about the Making of Beer
Dwight E. Matthews
Departments of
Chemistry & Medicine
University of Vermont
Burlington, VT
1
Observations from
Morrison and Boyd, Organic Chemistry

The first chemical synthesis by man was the production
of ethanol by fermentation

Ethanol production preceded the synthesis of soap

Conclusion:
Man’s desire for intoxication precedes man’s desire for
cleanliness
2
copyright 2013 DE Matthews
1
The Secret to Fermentation Is Yeast

Yeast are unicellular fungi

For fermentation (beer):
Saccharomyces cerevisiae

Originally isolated from the skins
of grapes

Yeast will convert simple sugars
to energy for their growth and to
by-products:

Ethanol (CH3-CH2-OH)
3
Ethanol Is Produced By Biological
Fermentation of Sugars



Organisms from yeast to humans degrade sugars (glucose) for
energy using O2 to produce CO2
The energy produced allows production of other carbon compounds
for growth
Under anaerobic conditions, yeast will stop the process short,
producing ethanol, a 2-carbon alcohol
4
copyright 2013 DE Matthews
2
Ethanol Is Produced By Biological
Fermentation of Sugars



Organisms from yeast to humans degrade sugars (glucose) for
energy using O2 to produce CO2
The energy produced allows production of other carbon compounds
for growth
Under anaerobic conditions, yeast will stop the process short,
producing ethanol, a 2-carbon alcohol
Sidelight: Ethanol is toxic to many cell types,
but yeast can exist in >12% (2.5 M) ethanol.
Ethanol production may be a yeast anti-biotic/fungal
to eliminate competing organisms.
5
Yeast to Humans: Can Synthesize and
Metabolize a Range of Sugars

Sugar [(CH2O)n where n = 6]



is produced by plants and animals
and stored as complex carbohydrates (saccharides)
Both yeast & humans can break disaccharides to simple
sugars
6
copyright 2013 DE Matthews
3
Some Carbohydrates Cannot be Broken Down
by Yeast or Humans


The arrangement of the bonds connecting the sugars is key
Cellulose has a β glucose linkage that resists cleavage
α(1→4)
β(1→4)
β(1→4)
7
Most Sugar in Plants is in the Form of a
Complex Carbohydrates, i.e. Polysaccharides



OH
Polysaccharides in plants:
H2C
Cellulose – not digestible


O
HO
Polysaccharides in seeds and fruits of plants (starch):
HO
Amylose: 1→4 linked glucose
Amylopectin: 1→4 and some 1→6 linked glucose
OH
OH
-D-Glucopyranose
(Glucose or Dextrose)
HO
H2C
O
O
HO
HO
H2C
O
O
H2C
HO
H2C
OH
OH
α(1→4)
O
Amylose
O
HO
HO
H2C
OH
HO
O
O
OH
O
O
HO
O
HO
H2C
OH
α(1→6)
OH
O
O
O
HO
HO
Amylopectin
H2C
OH
O
O
HO
OH
O
copyright 2013 DE Matthews
4
Seeds and Fruits Contain Enzymes to Digest
Starch
Amylase enzymes digest both amylose & amylopectin to glucose

The enzymes are active in ripening fruit or can be activated by
warming (e.g. grains)

HO
H2C
O
O
HO
HO
H2C
OH
O
O
HO
HO
Amylose
OH
H2C
O
OH
O
O
HO
HO
H2C
HO
α(1→4)
H2C
O
O
O
OH
HO
H2C
OH
HO
OH
O
O
OH
O
HO
α(1→6)
H2C
OH
OH
-D-Glucopyranose
(Glucose or Dextrose)
O
O
HO
HO
H2C
OH
Amylopectin
O
O
HO
OH
O
Enzymatic Digestion of Starch to Sugars in
Plants

Enzymes (e.g. amylases) breakdown starches:



[α-amylase]: Produces disaccharides (e.g. maltose)
[β-amylase]: Produces single sugars (glucose) from the ends
[Limit dextrinase]: Cleaves at the 1-6 branch points
CH2OH
C
HC
O
CH2OH
C
O
HC
CH
OH
H
C
C
H
O
1-4 link
OH
OH
C
H
CH2OH
O
C
CH
H
C
HC
O
OH
OH
CH2OH
O
C
CH
OH
H
C
C
H
OH
Amylose
HC
O
CH
OH
O
H
C
C
H
OH
OH
Maltose
CH2OH
CH2OH
C
HC
C
CH
OH
H
C
C
H
O
C
CH2OH
O
O
HC
1-6 branch
OH
OH
CH2OH
C
HC
O
OH
C
H
CH2
O
C
CH
H
C
OH
10
HC
O
1-4 link
OH
OH
C
H
C
H
HC
O
H
C
O
OH
CH2
C
CH
H
C
OH
Amylopectin
OH
CH
O
HC
O
OH
Isomaltose
OH
OH
C
H
C
H
O
H
C
C
H
O
H
OH
-D-Glucose
O
CH
H
C
OH
OH
But some polysaccharide
pieces may still remain
copyright 2013 DE Matthews
5
Yeast Can Metabolize Simple Sugars Easily For
Growth (but Polysaccharides Less Well)
CO2
O2
G
G
G
Yeast
Sugars
(starch)
C2H5OH
11
Methanol



What is it?
How does it form in the
fermentation process
How does it get in
distilled spirits
12
copyright 2013 DE Matthews
6
Methanol As A By-Product of Fermentation

Methanol




Is a one-carbon alcohol
Also distributes across body water and all tissues
Is also metabolized in the liver by the same enzymes that metabolize ethanol
Methanol metabolism produces toxic compounds


Formaldehyde – embalming fluid
Formic acid – neurotoxic
 Causes headache, nausea, vomiting in lower doses
 Is toxic to the optic nerve and can cause blindness (“white lightning”)
O
H3C
OH
C
H2
O
H3C
Alcohol
dehydrogenase
Ethanol
"ethyl alcohol"
H3C
C
H
C
Aldehyde
dehydrogenase
Ethanal
"acetaldehyde"
OH
Ethanoic acid
"acetic acid"
O
H3C
OH
H2C
O
HC
Alcohol
dehydrogenase
Methanol
"methyl alcohol"
OH
Methanal
"formaldehyde"
Methanoic acid
"formic acid"
Reactive
& Toxic
TOXIC
13
Legal Limits for Methanol

European methanol (MeOH) limit in ethanol (EtOH):


US ATF methanol limit in ethanol:




10 g MeOH/L EtOH
7 g MeOH/L EtOH  7 mg MeOH/ml EtOH
2.8 mg MeOH/ml (40% EtOH)
 250 ml = 0.7 g MeOH
1.0 mg MeOH/ml (14% wine)
 750 ml = 0.75 g MeOH
International Organization of Vine and Wine (OIV)

0.2-0.4 mg MeOH/ml wine
14
copyright 2013 DE Matthews
7
Methanol Is Not Produced By Yeast
It Occurs Naturally in Pectin
Yeast metabolizes glucose to endproducts, but not to methanol
Plants also contain the
polysaccharide pectin


OH
O
O
Pectin is 1,4-linked α-Dgalacturonic acid (oxidized
galactose)
Most of the galacturonic acids in
pectin have been methylated




O
C
CH3
O
OH
O
OH
-D-Galacturonic acid
OH
O
O
OH
C
Pectin
O
HO
Pectin is high in fruit skins (grapes,
apples, …)
Potato is has pectin
OH
O
O
O
C
Pectin, isolated from fruit, is used
as a gelling agent for foods

OH
HO
HO
Pectin found in a variety of fruits

O
C
CH3
O
HO
OH
O
15
An Enzyme Release Methanol from Pectin
O

O
O
C
CH3
O

Pectinesterase
HO
OH
O
O

OH
C
Pectin
Enzymes in fruits that digest
pectin
O
HO
Pectinase – hydrolyzes the
1,4-linkages in pectin
Pectinesterase – hydrolyzes
the methyl ester on
galacturonic acid
OH
O
O
O
C
Pectinase
CH3
O
OH
HO
O
OH
C
OH
O
O
+
H3C OH
HO
OH
OH
-D-Galacturonic acid
Methanol
16
copyright 2013 DE Matthews
8
Methanol Content of Fermented and Distilled Beverages

Grains have very little pectin – the methanol content of beer &
distilled whiskeys made from grains is low

Fruits and some vegetables (potatoes) has significant amounts of
pectin
Methanol is naturally produced during the fermentation of high-pectin
fruits and vegetables


Methanol (bp: 65 °C) is not always/usually separated from ethanol
(bp: 78 °C) during distillation

Fermented fruit beverages (e.g. hard cider and wine) and distilled
products (e.g. apple & pear brandy/schnapps) may contain
significant amounts of methanol
17
Methanol Content of Different Products
1200
1000
6
Methanol (mg/L)
Methanol (mg/L)
5
800
600
4
3
2
1
0
400
Cold
Hollow
cider
200
ESB
German Belgian
lager
triple
Beers
0
Distilled
Spirits
Beers
18
copyright 2013 DE Matthews
9
The Goal for Fermentation is to Get Yeast to
Replicate
Replication (growth) requires


Energy – sugar
Nitrogen:
 Amino acids  Protein
 DNA

Phosphate
 DNA

Some minerals

Some oxygen
 Calcium

Yeast will not grow on pure
sugar alone
19
Seeds


Contain everything a plant needs to begin
growth
Nutrients





We can breakdown polysaccharides in seeds
that we eat


Sugar as polysaccharides
Nitrogen as protein
DNA and phosphate
Some fat (another energy source)
Pancreas secretes α-amylase
But, there is not enough simple sugar in most
seeds for yeast to sustain growth
20
copyright 2013 DE Matthews
10
The Trick for Man to Make Beer


Humans had learned to
cultivate grasses using the
seeds for food: wheat, barley,
etc.
But grass seeds do not
ferment


Yeast needs simple sugars
Solution: trick the grass seeds
into making simple sugars out
of their polysaccharides
21
Seed Germination Produces Food for the
Growing Plant-to-be

Germination begins when the
barley seeds are steeped in water

Cells begin producing proteins
from DNA


Including enzymes: amylases
Next: stop germination by drying
the seeds

Result: malt

The malt seeds can also be
heated in kilns to produce
different types of malt flavors

Malted seeds are then stored dry
until use
22
copyright 2013 DE Matthews
11
What Do You Call a Person That Produces Malt
from Grain?
23
What Do You Call a Person Produces Malt from
Grain?
A
maltster
24
copyright 2013 DE Matthews
12
What Do You Call a Person Produces Malt from
Grain?
A
maltster
 Note:
Brewers are almost never maltsters
25
Reinheitsgebot: German (Bavarian) Purity Law
of 1516

Brewing beer began in the
700’s?

Duke Wilhelm IV of Bavaria:


„Keinem Bier mehr Stücke
als allein Gersten, Hopfen
und Wasser verwendet
werden sollen“
“No beer ingredients other
than



barley,
hops,
water are to be used”
Reinheitsgebot was
designed to prevent
competition between
brewers & bakers for
wheat and rye
26
copyright 2013 DE Matthews
13
Reinheitsgebot: German (Bavarian) Purity Law
of 1516
 “No
beer ingredients
other than



barley,
hops,
water are to be used”
 Yeast
was not
identified until the
1857 by Pasteur
27
What the Brewer Does (step 0):
Select Good Water for Taste & for the Yeast

Modern times dilemma: city water
has chlorine




Oxidizes & kills yeast
Oxidizes grains & hops
Adds an undesired taste
Cation & anion profile

Some cations add stability & are
needed by yeast for growth

Grain adds potassium
Some cations to avoid
 Calcium (can be added)

 High sodium (softened water)
 High iron


Water pH & bicarbonate abundance
Water that tastes bad will make bad
beer

E.g. tannin & sulfur compounds
Water
Hardness
28
copyright 2013 DE Matthews
14
What the Brewer Does (step 1): Mash the Grain:
Produce Simple Sugars for the Yeast


Crack (crush) the malted barley
Soak the barley in water –the
“mash”

Mash temperature must be optimal
for enzyme activation (~150°F or
65°C)
 Amylases
 Proteases




Wait (~60 min) for starch
conversion to simple sugars
Drain off and save the sugar
water (the “wort”)
Rinse the grain to remove
residual sugar and add to the
wort
By-product of the wort: protein,
amino acids, phosphate and
other nutrients for the yeast
29
Barley Is One Determinate that Defines a Beer
Style
Barley Production for 2011
Country
Megatons
Russia
16.9
Ukraine
9.1
France
8.8
Germany
8.7
Spain
8.3
United Kingdom
5.5
Poland
3.3
Denmark
3.3
Belarus
2.0
Czech Republic
1.8
Base Barley Malt
 Continental
beers (e.g.
German &
Belgian) use
Continental
Pilsner

UK beers use
British pale
malt
30
copyright 2013 DE Matthews
15
What the Brewer Does (step 2):
Boil the Wort with Hops

Boil the wort to sterilize and
remove unwanted volatile
compounds


Add hops to the boiling
wort




E.g. dimethyl sulfide
Adds taste, aroma
Adds antibacterial compounds
Boil ~60 minutes
Cool to room temperature
31
Hops

Are the female flower clusters of the
species Humulus lupulus


The hop plant is a perennial vine growing
>20 ft high



Displacing “gruit” herb blends
Hop cones are added to the wort



I.e. a weed
Cultivated since the 700’s
Used to make beer since the 1300’s


The flowers are the hop cones
To stabilize beer (antibiotic against bacteria)
To flavor beer, imparting a bitter, tangy
flavor
In 1442 Christopher, king of Bavaria,
Denmark & Sweden/Norway, required all
farmers to have “40 poles” for growing
hops
32
copyright 2013 DE Matthews
16
Hops and Alpha- & Beta-Acids

Yellowish pollen
containing hop oil inside
flowers

Hop oil contains both



Alpha-acids &
Beta-acids
Alpha- & Beta-acids are
a complex set of
molecules
33
Structures of Hop Alpha & Beta Acids




Relatively insoluble in water
The variable part is the blue group
Different acids give different aromas/taste
Common groups:



-CH2CH(CH3)2 – shown for α & β below
-CH(CH3)2 – cohumulone & colupulone
-CH(CH3)CH2CH3 – adhumulone & adlupulone
OH
O
HO
O
OH
HO
O
O
OH
n-Humulone
34
-acid)
Lupulone
-acid)
copyright 2013 DE Matthews
17
Boiling Hops in Wort Isomerizes α-Acids

Bitterness is based upon the isomerized α-acids


β-acids do not isomerize
Adding hops late in the wort boil preserves the α-acids
35
Hops Also Define a Beer Style
Hop Production for 2011
Country
Tons
Germany
38,068
Czech Republic
6,088
Poland
2,580
Slovenia
2,154
UK
1,622
Albania
1,307
Spain
1,048
Ukraine
680
France
648
Austria
451
Russia
350
Slovakia
249
Belgium
229
36
copyright 2013 DE Matthews
18
The Hop Profile of Beer Has Several
Components
Floral



The aroma
components 
The amount of hops
added
Spicy
Piney
When the hops are
added to the “boil”


Fruity
Citrus
Hallertau
Earthy
Herb
Early add: bittering
Late add: aroma
Fuggle (UK)
Saaz
Cascade (USA)
37
What the Brewer Does (step 3):
Add Yeast to Cooled Wort and Ferment

Yeast cells rapidly proliferate



Yeast metabolism produces



CO2
And ethanol, as an anaerobic byproduct
As available sugar is depleted,




Using available O2
Using available sugar
Yeast cells stop replicating
Yeast cells die or go dormant
(flocculate)
Ethanol production stops
Must maintain sanitation from
start to finish: don’t grow molds
or bacteria too
38
copyright 2013 DE Matthews
19
The Fermentation Conditions Affect Yeast and
the Characteristics of the Final Beer

Yeast produce >500
metabolites
CO2
Factors that affect yeast
flavor & aroma metabolites

G
Grains used
G
 and hops
G
Yeast
Sugars

Strain of yeast

Temperature of
fermentation
 Rate of proliferation

Other
Metabolites
Acetaldehyde
Amount of extra sugars
added
Diacetyl
Acetone
Fusel alcohols
(propanol)
39
Fusel* Alcohols Produced
*Larger than ethanol. Fusel is German for “bad hooch”

Adds “warming” solvent flavor
Higher in ale than lager

Common fusel alcohols:


n-Propanol

i-Butanol

Isoamyl alcohol
“Active” amyl alcohol

 Both amyls give a banana flavor
 Are common in wine
H2
C
HO
C
H2
CH3
OH
CH
H3C
C
H2
CH3
CH3
H2
C
HO
CH
CH3
C
H2
CH3
HO
CH
C
H2
C
H2
CH3
40
copyright 2013 DE Matthews
20
Esters Produced

Ethyl acetate



Fruity solvent taste
CH3
CH3
H2
C
C
Banana flavor
Apple flavor
O
O
H3C
CH
C
H2
O
CH3
O
Ethyl caproate

H2
C
C
H3C
Isoamyl acetate


O
H2
C
H3C
H2
C
C
H2
H2
C
C
O
C
H2
CH3
Greater in ale than lager

↑ with fermentation
temperatures
41
Ketones Produced
 Acetone
 Solvent taste
O
C
H3C
 Vicinal diketones (VDK)
 gives a “slickness” to mouth feel
 buttery, butterscotch flavor
 Taste threshold: 0.1 ppm

Diacetyl
 2,3-butanedione
CH3
O
C
H3C
C
CH3
O

O
2,3-Pentanedione
H2
C
C
H3C
C
CH3
O
42
copyright 2013 DE Matthews
21
Organic Acids Produced

Can give a bad taste/smell
O

Acetate
C
H3C
OH
 Vinegar

Propionate

Lactate
O
H3C
C
C
H2
OH
O
H3C
 Sour
C
H
C
OH
OH

O
Butyrate
H2
C
H3C
 Bad, rubbery

Caproate
 Bad, sour milk
C
C
H2
OH
O
H2
C
H3C
H2
C
C
H2
C
C
H2
OH
43
Phenols Produced

Phenol

4-Vinyl guaiacol (4VG)

Normally undesirable. Tastes:




Exceptions:



Medicinal
Plastic, band-aid, “phenolic”
Smoky
Hefeweizen – adds clove
Rauchbier – adds smoke
4VG is produced from yeast with a
“phenolic off-flavor” (POF) gene




Malt & hops have ferulic acid
POF codes for ferulic acid decarboxylase
Many cultivated yeasts do not have the POF
gene
Wild yeasts have the POF gene
44
copyright 2013 DE Matthews
22
Sulfur-Containing Compounds Produced

Hydrogen sulfide


Dimethyl sulfide (DMS)





from S-methyl methionine
cooked corn or cabbage smell
Dimethyl sulfoxide (DMSO)


Rotten egg smell
Bacteria reduce DMSO to DMS
Sulfur dioxide
Mercaptans
Volatile S compounds lost


During wort boil
By CO2 production during fermentation

Lager (colder fermentation) has more
volatile S compounds than ale
45
The “Lightstruck Flavor” (LIF) in Beer


LIF is a skunky smell
Occurs in beer exposed to
sunlight



Clear bottles bad
Brown bottles much less
Not present in beer lacking
hops

Hops play a part in producing
LIF
The skunky mercaptan culprit:
3-methylbut-2-ene-1-thiol (MBT)


Present in
 Skunk spray
 Durian fruit

But how is it produced?
46
copyright 2013 DE Matthews
23
Photochemical Production of the Precursor
Radical to form MBT

EPR study by K Huvaere
et al., J. Agric. Food
Chem. 53:1489 (2005)

Demonstrates
photoactivation of
riboflavin (RF) and etransfer to iso-α-acids

Produces a 2-methylbut2-ene radical

Known to react with H2S to
form MBT:
47
The American Homebrewers Association Beer
Judge Scoresheet (BSS)
 The
Score sheet
has a section for
descriptor tastes
and aromas
48
copyright 2013 DE Matthews
24
Some of the Negative Descriptors on the Beer
Scoresheet and the Compounds that Cause Them

Acetaldehyde


Diacetyl

DMS (dimethyl sulfide)

Estery







Phenolic

Butter, butterscotch
Sweet cooked canned corn
Fruits & roses – esters & amyl
alcohols

Fresh cut grass or green leaves
cis-3-hexanal by bacteria on barley
(before the wort)
Spicy (clove, pepper), smoky, plastic
– phenols
Solvent

Sour/acidic





Fusel alcohols, ethyl acetate
Clean – lactic acid
Vinegar-like – acetic acid
Can be bacterial contamination
Sulfur

Rotten eggs, burning matches – H2S
 Bacterial contamination
Skunky aroma – MBT
Metallic
Musty
Stale, cardboard, sherry-like

Light-struck


Oxidized
Grassy



Green apple

Vegetal

Cooked, canned or rotten vegetable
aroma – DMS+H2S
 Bacterial contamination
49
Beer Is All About the Yeast (Hefe in German)
 Long
before yeast
was identified,
brewers knew they
needed sediment from
the prior fermentation
to start the next
fermentation
 Reusing yeast from
batch to batch tends
to select for specific
strains of yeast
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25
What Are the Differences Between
 Ale
Yeast
 Lager
1.
1.
2.
2.
3.
3.
?
Yeast
?
51
Ale Yeast vs. Lager Yeast
Ale yeast “top ferments”
 Lager yeast “bottom
ferments”


Ale yeast


Clumps during growth
and rises (via CO2
bubbles) to the top
Flocculates to the bottom
(but so does lager yeast)
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26
Munich Germany Is Cold in the Winter
Low temperature
map for
14-Feb-2013
53
Cold Fermentation Temperatures Select for
Cold Temperature Yeasts
Brewer’s and baker’s yeast:
Saccharomyces cerevisiae
and
 A cold-tolerant yeast strain: S.
bayanus


Ale
Used in wine & cider production
combined to make

S. pastorianus



Lager yeast
Purified by Emil Hansen in 1883
at the Carlsberg Laboratory in
Denmark
Belgian
Ale
14°C
57°F
Ideal fermentation temperature:
 8-13 °C (46-55 °F)
Lager
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27
Cold Temperature Fermentation Was Codified
into Law in Bavaria in 1553
Duke Albrecht V of
Bavaria

(son of Willem IV)
restricted beer brewing
to the Reinheitsgebot
dates:
Sept 23 [Feast of St.
Michael]
through
 April 23 [Feast of St.
George]

 Two
months, same
beers:


Octoberfest bier
Märzen bier
55
Cold Temperature Fermentation Limits
Bacterial Contamination
Because lager beer does
not sour as quick:
 Can ship lager
 Growth of German
breweries
 Late 1800’s lager boon:


Carlsberg isolates lager
yeast (S. pastorianus)
Refrigeration equipment
invented
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28
What the Brewer Needs to Make Good Beer

Good water

Malted grains (barley)


The commercial maltster controls this process
But, a wide variety of malted grains available

Good mashing process (to extract sugar from malt)

Hops


Great variety of hops and alpha-acid profiles
Yeast

Very wide range of yeast strains and characteristics
available

Sanitary conditions

Fermentation conditions

A taste for really good beer
57
Greg Noonan 1951-2009

Founder of the Vermont Pub
& Brew

Inventor of new beer styles


Author



The black IPA
Brewing Lager Beer
A major influence on both
home and micro brewers
Famous quote: “It’s about
the beer”
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Good Sources:

How to Brew, John J.
Palmer

http://www.howtobrew.com/

Brewing Classic Styles,
Jamil Zainasheff, John J.
Palmer

The Complete Joy of
Homebrewing, Charles
Papazian
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