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The Chemistry of Beer

Jim EnterkinLDM group Special Talk

5/22/09

Outline

• History• Ingreedients– Barley, Hops, Yeast, Water

• Brewing process– The processing, and what effects we expect them

to have on properties of the final product• Beer characteristics– The properties that we observe, and how they

were derived from the processing of the ingredients

• Conclusion & links for more info

History

• Beer is older than recorded history– How and when it was discovered is unknown– Evidence that barley was used for fermentation

prior to the baking of bread– Likely accidental discovery:• Grain at some stage of germination immersed in water• Wild airborne yeasts land in water• Natural fermentation• Some brave soul drinks this water• Not only was it tasty, but it got him/her buzzed!!!!

History

• Beer is the reason for civilization as we know it– Civilization depended upon nomads settling into

villages– Nutrition and longevity actually decreased as

humans moved into farming villages– Main reason to settle into villages was a steady

supply of grain– Why would the steady supply of grain be important

enough to endure worse nutrition and shortened lifespan?

History

• Beer improved health and hygiene– Especially in populated areas, water was often

highly contaminated– Beer is completely safe• No organisms that are harmful to humans can survive

in beer• Combination of alcohol, pH, and CO2 content

History

• Ancient Babylon– 4000 BC

• Sophisticated brewing techniques• Beer integrated into religious ceremonies

– 2000 BC• More than a dozen beer styles from various ingredients

• Ancient Egypt– Beer brewed, sold, and served exclusively by female

“brewsters”– “Brewsters” held high social status

History

• Middle Ages– Beer as important as bread in diet– Beer brewed in the home or in monasteries– Monasteries advanced brewing techniques• For the nutritional needs of monks and pilgrims• Gained reputation for superior quality beer• Sale of beer helped fund monasteries

– Some communal brewhouses arise by late middle ages

History

• Colonial America– Beer brewed mostly by women– Beer brewed mostly in the home– Brewing of beer in was a standard household

activity, like baking bread

History

• Uniformity of lager beers– Industrial Revolution• Trains and refrigeration lead to mass produced and

shipped beer

– Prohibition and the depression lead to consolidation of the industry

History

• Revival of Beer– 1971, England, CAMRA (CAMpaign for Real Ale)– Cold War• Americans stationed in Europe experience different

styles of beer

– 1979, USA, legalization of homebrewing– Today: Craft brews is the fastest growing segment

of the beverage industry

History

• Louis Pasteur (1822 – 1895)– Work in microbiology stemmed largely from

desire to understand role of yeast in fermentation• Disproved spontaneous generation• Developed germ theory• Pasteurization• Anaerobic respiration

• S. P. L. Sorenson (1868 - 1939)– Developed pH scale for more accurate control of

wort production (1909)

Outline






Types of Grain• 2-row Barley– Higher extract, less husk– Preferred by craft brewers,

home brewers, and Europeanbreweries

• 4-row Barley– Used only as cattle feed

• 6-row Barley– Preferred by large U.S. breweries– Yields more amylases to help break down the cheap

adjuncts (i.e. rice and corn)• Other Grains– Wheat, Oats, Corn, Rice

http://www.extension.umn.edu/distribution/cropsystems/components/7658-9.html

http://www.extension.umn.edu/distribution/cropsystems/components/7658-9.html

Malting

• Grain (usually barley) is malted– Harvested grain is soaked in water until it

germinates• This activates amylases (and proteases)

– Grain is dried• This halts the conversion

– Acrospires (sprouts) are removed– Grain is cured• usually at least one month

http://www.scientiaevitae.de/gb/2/5/beer.htm

Barley Amylase

Barley Modification• Acrospires eat endosperm as they

grow during malting– Acrospire is the sprout, endosperm

is its food source (full of starch)– Acrospires will continue to eat

endosperm until it is depleted or they are stopped by the maltster by heating and drying

– Longer acrospire growth leads to:• More endosperm consumed and less

fermentable sugar• More amylases are activated• More yeast nutrients released• Clearer beer and more complete

fermentationhttp://www.scientiaevitae.de/gb/2/5/beer.htm

Malting

• Toasting or Roasting– Varying heats – hotter for darker malts– Varying times– Varying fire sources

Malt

• Germinated and crushed grain• Amylases (and proteases) accessible but

inactive• Starches from endosperm partially broken

down

Hops

• Used in continental Europe since 700s AD• Introduced to Britain in 1500s by Flemish

immigrants• Didn’t replace use of other herbs for over 200

years after– Bog myrtle, horehound, alehoof, buckbean,

wormwood

Hops

• Humulus lupulus (family = Cannabinaceae)• Perennial vine• Flowers of female plant grow into strobiles

(cones) composed of leaflike bracts and bracteoles

• Bracteoles have lupulin glands• Lupulin glands produce resins containing alpha

acids• These provide bitter flavor and act as a

preservative• Oils from the plant add flavor and aroma

Alpha Acids

• Humulone R = CH2CH(CH3)2

• Cohumulone R = CH(CH3)2

• Adhumulone R = CH(CH3)CH2CH3

Hops

• Bitter herb grown on a vine• Alpha acids – bitter taste and preservative• Aromatic oils

Yeast

• The most mysterious ingredient for most of the history of beer, but also the most important

• Called “God is good” by medieval brewers as it turned wort into beer and produced more of itself

• It is unknown whether yeast or dogs were the first domestic animal

Yeast

• Through anaerobic respiration, it converts the malt sugar into alcohol, CO2, and other by-products

• Often removed after fermentation, and can be re-uesd

• Yeast is essentially a fermentation catalyst• The word “enzyme” (meaning biological

catalyst) originates from the Greek for “within the yeast”*

*http://www.biotech.seagrant.org/glossary.html

Yeast

• 2 main types (for brewing purposes)– Saccharomyces cerevisiae (ale yeast)• Prefers warmer temperatures (20-25°C) and will

flocculate on top of the beer

– Saccharomyces uvarum (lager yeast)• Prefers cooler temperatures and will flocculate at the

bottom of the beer (~5°C)

Yeast

• Fermentation catalyst

Water

• 3 main concerns– Flavor of water– Nutrients for yeast

• Can’t use distilled water– pH effects how well enzymes make maltose

• Keep mash pH 5-5.5

• Ion concentration important– e.g. Ca2+, Mg2+, CO3

2-

• Darker malts lower pH more than lighter malts– Areas with water with natural higher pH (e.g. Ireland)

produced darker beers than areas with water with lower pH (e.g. Czech Republic)

Water

• The medium for fermentation

Outline






Brewing Process

• Sugar is extracted from grains• Hops are added and wort is boiled• Wort is cooled• Yeast is added• Wort ferments to become beer

Mashing & Lautering• Mashing– Malt is soaked in hot water– ~155°F (~68°C)– Amylases re-activated– starches broken down to sugars

• Primarily maltose = 2 glucose joined by α(14) linkage– Proteins also broken down– Processing of proteins and starches highly dependent

on temperature– pH also important for amylase activity

• Lautering– Grains are rinsed until water comes through clear– Extract all ingredients into wort to be boiled

Boil

• Denatures and inactivates amylases– Breakdown of starches halted– Most proteins coagulate and settle out and can be

removed• Hot break

• Extracts alpha acids and oils from hops• Isomerizes alpha acids to isoalpha acids• Kills any microbes in the wort• Caramelization of sugars

Alpha Acid Isomerization

http://www.scielo.br/scielo.php?pid=S0100-40422000000100019&script=sci_arttext

Pitching Yeast

• Addition of yeast to allow fermentation• Wort must be at proper temperature for yeast

to survive and flourish– Slightly off temperatures lead to off flavors– Far off temperatures lead to stuck fermentation

• Oxygen must be kept out– Yeast only converts sugars to alcohol and CO2

under anaerobic respiration– With oxygen present, aerobic respiration will

dominate

Fermentation

• Yeast absorbs oxygen and sugar, and reproduces asexually

• When oxygen is used up, reproduction stops and fermentation (anaerobic respiration) begins

• Each glucose produces two molecules of ethyl alcohol and CO2

– C6H12O6 2 CH3CH2OH + 2 CO2 + 118 kJ (2 ATP)

• Large amounts of CO2 are produced and must be removed without letting oxygen in– Airlock or water bubbler

Fermentation

• When all fermentable sugars have been consumed, fermentation stops and yeast begins to go dormant

• Yeast settle out and the beer clarifies• This yields a “young beer”– Bad taste and smell– High concentrations of diacetyl and other organic

byproducts

Conditioning

• Small amounts of remaining yeast continue to consume byproducts of initial fermentation– Conditioning or aging, development of flavor

Packaging

• Flat beer is packaged (bottle or keg) and must be carbonated– Add extra sugar for natural carbonation by

fermentation– Artificially carbonate from gas source

Outline






Beer Characteristics

• Alcohol Content• Flavor– Malt, Hops, Yeast, Water

• Aroma• Clarity• Head• Preservation

Alcohol Content

• Measured by density– Original gravity – density of wort prior to

fermentation– Final gravity – density of beer after fermentation– Dissolved sugars lead to high density– As sugars convert to ethyl alcohol, the density

decreases– The decrease in the density is directly

proportional to the amount of alcohol present

Flavor

• Sweet flavors from malt– Dependent on types of grain and on grain

modification• Bitter flavors from hops– Isoalpha acids balance sweetness of grain• 15 – 100 ppm depending on beer type

– Aroma from hop oils mainly from later additions of hops

Aroma

• Hop oils– Small organic molecules• Often aromatics• Polyphenols

• Mainly from late addition of hops– Aroma hops boiled for a short time (~5 minutes)– Dry hops (added after wort has cooled or just

before packaging)

Phenol

Clarity

• Filtering, siphoning, settling, racking• Yeast– Flocculency of yeast

• Polyphenols from hops– Larger polyphenols become insoluble and form a

“permanent haze”– Small polyphenols agglomerate when chilled to

form a “chill haze”

Head

• Protein from grains– Wheat proteins stabilize head

• Isoalpha acids– Tensioactive properties of isoalpha acids stabilize

head

Preservation

• Alcohol is a natural preservative• Alpha acids– Act as a preservative by inhibiting the growth of

bacteria– Beta acids (also from hops) also help

• Decomposition on exposure to light– Isoalpha acids are

light sensitive– Skunky flavor– Only a few ppb

http://www.scielo.br/scielo.php?pid=S0100-40422000000100019&script=sci_arttext

Outline






More Info

• Stephen Snyder, The Brewmaster’s Bible, New York: HarperPerennial, 1997

• http://www.scientiaevitae.de/gb/2/5/beer.htm

• Hop Chemistry: http://www.scielo.br/scielo.php?pid=S0100-40422000000100019&script=sci_arttext

Drink!

• And be merry• Happy Memorial Day!