Nondairy Fermented Foods and Products
183
starch, a necessary part of beer brewing includes a step whereby malt or other exogenous sources of
amylase are provided for the hydrolysis of starches to sugars. The malt is first prepared by allowing
barley grains to germinate. This serves as a source of amylases (fungal amylases may be used also).
Both β- and α-amylases are involved, with the latter acting to liquefy starch and the former to increase
sugar formation. In brief, the brewing process begins with the mixing of malt, malt adjuncts, hops, and
water. Malt adjuncts include certain grains, grain products, sugars, and other carbohydrate products
to serve as fermentable substances. Hops are added as sources of pyrogallol and catechol tannins,
resins, essential oils, and other constituents for the purpose of precipitating unstable proteins during
the boiling of wort and to provide for biological stability, bitterness, and aroma. The process by which
the malt and malt adjuncts are dissolved and heated and the starches digested is called mashing. The
soluble part of the mashed materials is called wort (compare with koji). In some breweries, lactobacilli
are introduced into the mash to lower the pH of wort through lactic acid production. The species
generally used for this purpose is L. delbrueckii subsp. delbrueckii.
39
Wort and hops are mixed and boiled for 1.5–2.5 hours for the purpose of enzyme inactivation, extraction of soluble hop substances, precipitation of coagulable proteins, concentration, and sterilization.
Following the boiling of wort and hops, the wort is separated, cooled, and fermented. The fermentation of the sugar-laden wort is carried out by the inoculation of S. cerevisiae. Ale results from the
activities of top-fermenting yeasts, which depress the pH to around 3.8, whereas bottom-fermenting
yeasts (S. “carlsbergensis” strains) give rise to lager and other beers with pH values of 4.1–4.2. A
top fermentation is complete in 5–7 days; a bottom fermentation requires 7–12 days. The freshly
fermented product is aged and finished by the addition of CO 2 to a final content of 0.45–0.52% before
it is ready for commerce. The pasteurization of beer at 140
◦ F (60
◦ C) or higher, may be carried out
for the purpose of destroying spoilage organisms. When lactic acid bacteria are present in beers, the
lactobacilli are found more commonly in top fermentations, whereas pediococci are found in bottom
fermentations.
39
The industrial spoilage of beers and ales is commonly referred to as beer infections. This condition is
caused by yeasts and bacteria. The spoilage patterns of beers and ales may be classified into four groups:
ropiness, sarcinae sickness, sourness, and turbidity. Ropiness is a condition in which the liquid becomes
characteristically viscous and pours as an “oily” stream. It is caused by Acetobacter, Lactobacillus,
Pediococcus cerevisiae, and Gluconobacter oxydans (formerly Acetomonas).
26,64,91 Sarcinae sickness
is caused by P. cerevisiae, which produces a honeylike odor. This characteristic odor is the result of
diacetyl production by the spoilage organism in combination with the normal odor of beer. Sourness
in beers is caused by Acetobacter spp. These organisms are capable of oxidizing ethanol to acetic acid,
and the sourness that results is referable to increased levels of acetic acid. Turbidity and off-odors in
beers are caused by Zymomonas anaerobia (formerly Achromobacter anaerobium) and several yeasts
such as Saccharomyces spp. The growth of bacteria is possible in beers because of a normal pH range
of 4–5 and a good content of utilizable nutrients.
Some Gram-negative obligately anaerobic bacteria have been isolated from spoiled beers and pitching yeasts, and the six species are represented by four genera:
Megasphaera cerevisiae
Selenomonas lacticifex
Pectinatus cerevisiiphilus
Zymophilus paucivorans
P. frisingensis
Z. raffinosivorans
All but M. cerevisiae produce acetic and propionic acids, and S. lacticifex also produces lactate.
73
Although M. cerevisiae produces negligible to minor amounts of acetic and propionic acids, it produces
large quantities of isovaleric acid in addition to H 2 S.
23 P. cerevisiiphilus was the first of these to be
183
starch, a necessary part of beer brewing includes a step whereby malt or other exogenous sources of
amylase are provided for the hydrolysis of starches to sugars. The malt is first prepared by allowing
barley grains to germinate. This serves as a source of amylases (fungal amylases may be used also).
Both β- and α-amylases are involved, with the latter acting to liquefy starch and the former to increase
sugar formation. In brief, the brewing process begins with the mixing of malt, malt adjuncts, hops, and
water. Malt adjuncts include certain grains, grain products, sugars, and other carbohydrate products
to serve as fermentable substances. Hops are added as sources of pyrogallol and catechol tannins,
resins, essential oils, and other constituents for the purpose of precipitating unstable proteins during
the boiling of wort and to provide for biological stability, bitterness, and aroma. The process by which
the malt and malt adjuncts are dissolved and heated and the starches digested is called mashing. The
soluble part of the mashed materials is called wort (compare with koji). In some breweries, lactobacilli
are introduced into the mash to lower the pH of wort through lactic acid production. The species
generally used for this purpose is L. delbrueckii subsp. delbrueckii.
39
Wort and hops are mixed and boiled for 1.5–2.5 hours for the purpose of enzyme inactivation, extraction of soluble hop substances, precipitation of coagulable proteins, concentration, and sterilization.
Following the boiling of wort and hops, the wort is separated, cooled, and fermented. The fermentation of the sugar-laden wort is carried out by the inoculation of S. cerevisiae. Ale results from the
activities of top-fermenting yeasts, which depress the pH to around 3.8, whereas bottom-fermenting
yeasts (S. “carlsbergensis” strains) give rise to lager and other beers with pH values of 4.1–4.2. A
top fermentation is complete in 5–7 days; a bottom fermentation requires 7–12 days. The freshly
fermented product is aged and finished by the addition of CO 2 to a final content of 0.45–0.52% before
it is ready for commerce. The pasteurization of beer at 140
◦ F (60
◦ C) or higher, may be carried out
for the purpose of destroying spoilage organisms. When lactic acid bacteria are present in beers, the
lactobacilli are found more commonly in top fermentations, whereas pediococci are found in bottom
fermentations.
39
The industrial spoilage of beers and ales is commonly referred to as beer infections. This condition is
caused by yeasts and bacteria. The spoilage patterns of beers and ales may be classified into four groups:
ropiness, sarcinae sickness, sourness, and turbidity. Ropiness is a condition in which the liquid becomes
characteristically viscous and pours as an “oily” stream. It is caused by Acetobacter, Lactobacillus,
Pediococcus cerevisiae, and Gluconobacter oxydans (formerly Acetomonas).
26,64,91 Sarcinae sickness
is caused by P. cerevisiae, which produces a honeylike odor. This characteristic odor is the result of
diacetyl production by the spoilage organism in combination with the normal odor of beer. Sourness
in beers is caused by Acetobacter spp. These organisms are capable of oxidizing ethanol to acetic acid,
and the sourness that results is referable to increased levels of acetic acid. Turbidity and off-odors in
beers are caused by Zymomonas anaerobia (formerly Achromobacter anaerobium) and several yeasts
such as Saccharomyces spp. The growth of bacteria is possible in beers because of a normal pH range
of 4–5 and a good content of utilizable nutrients.
Some Gram-negative obligately anaerobic bacteria have been isolated from spoiled beers and pitching yeasts, and the six species are represented by four genera:
Megasphaera cerevisiae
Selenomonas lacticifex
Pectinatus cerevisiiphilus
Zymophilus paucivorans
P. frisingensis
Z. raffinosivorans
All but M. cerevisiae produce acetic and propionic acids, and S. lacticifex also produces lactate.
73
Although M. cerevisiae produces negligible to minor amounts of acetic and propionic acids, it produces
large quantities of isovaleric acid in addition to H 2 S.
23 P. cerevisiiphilus was the first of these to be