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Lecture 15 Beverage Fermentation. Ales & Lagers. History. Chemical analysis of 7,000 year-old jugs puts invention of beer around the same time period as wine

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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.


Saccharomyces sp.

  • 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.

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 cervisiaeis 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”.

what qualities should my yeast have
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

Major Reaction: Glucose to Carbon Dioxide and Ethanol

Special flavors and aromas of beers arise from minor biochemical reactions

  • 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.


  • 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.
  • What’s 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.

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 α and β-acids, but α-acids contributes more to the bittering of a beer.

These oils are non-polar, and can only be extracted through a short boiling.


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.


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.


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.


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.


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.

fermentation systems
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
fermentation of ales
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.
fermentation of ales21
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.
fermentation of lager
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.
fermentation of lager23
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.
compounds produced in primary fermentation and not reduced during lagering
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.
    • 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
compounds produced in primary fermentation and reduced during lagering
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.

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.


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.


After fermentation the fermented wort, now called beer, is transferred through a filter.

The filter removes various proteins, hop residue and yeast cells.


From the filter, the beer moves to the beer servers.

These are carbonating tanks, holding tanks and serving tanks.