Lecture 15 Beverage Fermentation

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Lecture 15Beverage Fermentation

• Ales Lagers

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History
Chemical analysis of 7,000 year-old jugs puts
invention of beer around the same time period as
wine Addition of hops to beer occurred about one
thousand years ago but before the 14th century
spruce, ginger, wormwood, sage, and sweet mary
were more popular. 1516 Bavarian purity law
passed, oldest known food purity law still in
effect, limited ingredients of beer to hops,
barley, and water. 16th century lager beer type
accidentally invented during cold cave
fermentation. Beers in America were largely
heavy beers, until prohibition ended most
American breweries. Now the beer market is
nearly monopolized by Anheuser-Busch, who made a
fortune producing cheaper, watery, light beer for
women workers during World War II. The American
pallet now reflects this with preference for
lighter beer.
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Yeast
Saccharomyces sp.
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Yeast

• It is usual to select strains of yeast for
  brewing from yeasts already in commercial use.
• Some breweries isolate, select and maintain their
  yeast strains but others engage specialist
  laboratories to provide this service.
• Can make a stock of your yeast.

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Yeast can be found naturally on the surface of
most plants including barley seeds. Wild
yeast will most likely produce flavors that are
undesirable. During the fermentation process,
undesirable microbes must be kept out of the beer.
Saccharomyces cervisiae is the species most often
used for ales, its optimum fermentation
temperature is 16-24 C Saccharomyces uvarium is
largely used in lagers, and steam beers. The
optimum temperature for this fermentation is 2-13
C
Over a 15 square mile area near Brussels the
resident wild yeast and bacterial populations are
perfect for spontaneously fermenting, beer. This
fruity sour beer is known as a lambic.
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What qualities should my yeast have?

• Rapid initiation of fermentation
• High fermentation efficiency
• High ethanol tolerance
• Desired flavor characteristics
• High genetic stability
• Range of alcohol production

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Metabolism
Major Reaction Glucose to Carbon Dioxide and
Ethanol
Special flavors and aromas of beers arise from
minor biochemical reactions
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Yeast

• In the average brewery, a large inoculum of cells
  is used (ca 5-15 million cells/ml of wort).
• In each fermentation the cell density increases
  three-to-four-fold.
• Therefore, one-third to one-fourth of the yeast
  crop of each fermentation is used for inoculation
  of the next batch.

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Malt

• Made from barley that has been allowed to
  germinate.
• Germination converts starch in the seeds into
  simpler sugars. These sugars are extracted in the
  mashing process.
• This malt extract is then used by the yeast in
  the fermentation process.
• Before mashing the malt may be roasted to darken
  the color and harden a beer.

barley
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Wort

• Whats in it
• Brewers' wort (145) commonly has 8-14 total
  solids.
• 90-92 are carbohydrates glucose, fructose,
  maltose, sucrose, maltotriose.
• Nitrogenous compounds, such as, amino acids.
• Vitamins biotin, inositol, pantothenic acid,
  pyridoxine, and thiamine are present in wort and
  utilized by Brewers' yeast.
• Phosphates, chlorides, sulfates and other anions
  are present with the cations Na, K, Ca, Mg, Fe,
  Cu, and Zn.

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Humulus lupulus (hops)
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Hops are the flowering portion of the hop
vine. These flowers not only fight off bacterial
infections in the beer, they aid in clarification
of the beer, stabilize the flavor, help retain
head, and aid in ones ability to drink the beer.
Hop oils are produced in the Lupulin glands of
the flower. The oils are made of a and ß-acids,
but a-acids contributes more to the bittering of
a beer. These oils are non-polar, and can only
be extracted through a short boiling.
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Process
Malted Barley and Specialty Grains
Malted barley and specialty grains are run
through roller mill and cracked open. This
grist is then carried by an auger to the mash tun.
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Process
In the mash tun the grist is mixed with hot water
to form a mash. In the mash, enzymes that exist
in the grain become active and convert the
starches to fermentable sugar. The sugar rich
liquid from the mash, called wort, is drained
from the mash tun.
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Process
The wort is drained from the mash tun and moved
to the brew kettle. In the brew kettle the wort
is boiled and hops are added. From the hops we
can extract bitterness, which will help balance
the sweetness of the wort.
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Process
After boiling, the wort is transferred through a
chiller. While passing through the chiller the
wort is instantly chilled to the appropriate
temperature for fermentation.
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Process
From the chiller, the wort moves into a
temperature controlled fermenter. Yeast is
added and fermentation begins. In fermentation
the yeast will ferment sugars in the wort and
produce alcohol, carbon dioxide, and other flavor
compounds.
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Fermentation Systems

• Cylindroconical systems
• Produce ales and lagers.
• Conical base, and pressure systems.
• Open systems
• Used for the fermentation of ales
• Utilize skiming for repitching
• Carbon dioxide can diffuse out

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Fermentation of Ales

• Top fermenting-rise to the surface and create a
  think yeasty head.
• Warmer temps- 60-70F
• More rapid growth
• Create more esters
• Complex and Fruity
• Ales, porters, stouts, and wheat beers.

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Fermentation of Ales

• Lag phase is when yeast is building cell walls
  and reserves.
• Then yeast begin to divide.
• First visible sign of fermentation is bubbles
  starting to form, which spread until the surface
  is covered.
• After 18 hours the bubbles thicken and change to
  a light brown color.
• pH and specific gravity fall, and temperature and
  yeast count rise.
• Max fermentation is reached after 36-48 hrs.
• White yeast head on top, with CO2 escaping.
• Activity slows and the head changes from white to
  pale cream, as yeast rises to surface and
  replaces the foam.

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Fermentation of Lager

• Bottom fermenting-yeast settle to the bottom of
  the fermenter as fermentation reaches completion.
• Colder tempeatures 47-58F
• Slower growth
• Crisp and hoppy like a pilsner or sweet and malty
  like a Dopplebock.
• Examples Pilsners, Bocks, and American malt
  liquors.

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Fermentation of Lager

• Time-temperature profiles vary widely.
• Pitch the yeast at 5-60 C and raise to 8-90 C.
  This makes better beer because the low temps
  retard the development of by-products which are
  inappropriate in lager (esters, fusel alcohols,
  diacetyl).
• Lag period is longer at lower temperatures
  though.
• After primary fermentation the temperature is
  dropped by 1-1.5C each day and then is
  transferred to a lager cellar at 45-50C. The
  starting temp and the rate of temp increase can
  vary.

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Compounds produced in primary fermentation and
not reduced during lagering

• Fusel or higher alcohols
• By-product of amino acid metabolism.
• Levels are affected by yeast strain.
• Spicy, wine-like, and alcoholic taste.
• Organic acids
• Formed from carbohydrate metabolism
• Contribute to the sourness or acid taste (also
  pH) of beer.

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• Esters
• By-product of lipid metabolism in a reaction
  between an alcohol and intermediates of lipid
  synthesis.
• Usually impart a fruity character to the beer.
• There are two types
• Acetate esters
• ethyl acetate (solventy, fruity, sweet)
• isoamyl acetate (banana, fruity, sweet)
• phenethyl acetate (roses, honey, apple, sweet).
• Fatty acid ester
• ethyl caproate (apple, aniseed, sweet)
• ethyl caprylate (apple, fruity, sweet)
• Ale yeast strains produce more esters

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Compounds produced in primary fermentation and
reduced during lagering

• Diacetyl
• Byproduct of amino acid metabolism.
• Tastes like butter, butterscotch, and feels slick
  on the palate.
• Pentadione
• Similar to diacetyl.
• Milder flavor similar to honey or butter.

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• Acetaldehyde
• Intermediate of ethanol production.
• It can form in autolysis of yeast during lagering
  if yeast is in poor condition.
• It can also form if post-fermentation beer is
  exposed to air (oxygen).
• Ethanol can be oxidized to acetaldehyde.
• Acetoin
• Formed from a secondary reaction of alcoholic
  fermentation.
• Pyruvate decarboxylase converts pyruvate to
  acetaldehyde, which is then converted to ethanol
  and CO2.
• Pyruvate decarboxylase sometimes joins two
  acetaldehyde molecules to form acetoin.

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Process
After fermentation the fermented wort, now called
beer, is transferred through a filter. The
filter removes various proteins, hop residue and
yeast cells.
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Process
From the filter, the beer moves to the beer
servers. These are carbonating tanks, holding
tanks and serving tanks.
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