184 Modern Food Microbiology
associated with spoiled beer when it was isolated from turbid and off-flavor beer in 1978.
43 It has
since been found in breweries not only in the United States, but also in several European countries
and Japan. Among the unusual features of these organisms as beer spoilers is their Gram reaction and
obligately anaerobic status. Previously, the typical beer spoilers were regarded as being either lactic
acid bacteria or yeasts. Megasphaera and Selenomonas are best known as members of the rumen biota.
In addition to the organic acids noted above, Pectinatus spp. also produce H 2 S and acetoin. The beers
most susceptible to their growth are those that contain <4.4% alcohol.
With respect to spoiled packaged beer, one of the major contaminants found is Saccharomyces
diastaticus, which is able to utilize dextrins that normal brewers’ yeasts (S. “carlsbergensis” and
S. cerevisiae) cannot.
39 Pediococci, Flavobacterium proteus (formerly Obesumbacterium), and Brettanomyces are sometimes found in spoiled beer.
Wines
Wines are normal alcoholic fermentations of sound grapes followed by aging. A large number of
other fruits such as peaches, pears, and so forth may be fermented for wines, but in these instances the
wine is named by the fruit, such as peach wine, pear wine, and the like. Because fruits already contain
fermentable sugars, the use of exogenous sources of amylases is not necessary, as it is when grains
are used for beers or whiskeys. Wine making begins with the selection of suitable grapes, which are
crushed and then treated with a sulfite such as potassium metabisulfite to retard the growth of acetic
acid bacteria, wild yeasts, and molds. The pressed juice, called must, is inoculated with a suitable
wine strain of S. “ellipsoideus.” The fermentation is allowed to continue for 3–5 days at temperatures
between 70
◦ F and 90
◦ F (21
◦ C and 32
◦ C), and good yeast strains may produce up to 14–18% ethanol.
58
Following fermentation, the wine is racked–that is, drawn off from the lees or sediment, which contains
potassium bitartrate (cream of tartar). The clearing and development of flavor occur during the storage
and aging process. Red wines are made by initially fermenting the crushed grape must “on the skins”
during which pigment is extracted into the juice; white wines are prepared generally from the juice of
white grapes. Champagne, a sparkling wine made by a secondary fermentation of wine, is produced
by adding sugar, citric acid, and a champagne yeast starter to bottles of a previously prepared, selected
table wine. The bottles are corked, clamped, and stored horizontally at suitable temperatures for about
6 months. They are then removed, agitated, and aged for an additional period of up to 4 years. The
final sedimentation of yeast cells and tartrates is accelerated by reducing the temperature of the wine to
around 25
◦ C and holding for 1–2 weeks. Clarification of the champagne is brought about by working
the sediment down the bottle onto the cork over a period of 2–6 weeks by frequent rotation of the
bottle. Finally, the sediment is frozen and disgorged upon removal of the cork.
Table wines undergo spoilage by bacteria and yeasts with Candida valida being the most important
yeast. Growth of this organism occurs at the surface of wines, where a thin film is formed. The
organisms attack alcohol and other constituents from this layer and create an appearance that is
sometimes referred to as wine flowers. Among the bacteria that cause wine spoilage are members of
the genus Acetobacter, which oxidize alcohol to acetic acid (produce vinegar). The most serious and
the most common disease of table wines is referred to as tourne disease. Tourne disease is caused
by a facultative anaerobe or an anaerobe that utilizes sugars and seems to prefer conditions of low
alcohol content. This type of spoilage is characterized by an increased volatile acidity, a silky type
of cloudiness, and later in the course of spoilage, a “mousy” odor and taste caused by Brettanomyces
spp. commonly found in Bordeaux wines.
Malo-lactic fermentation is a spoilage condition of great importance in wines. Malic and tartaric acids are two of the predominant organic acids in grape must and wine, and in the malolactic
associated with spoiled beer when it was isolated from turbid and off-flavor beer in 1978.
43 It has
since been found in breweries not only in the United States, but also in several European countries
and Japan. Among the unusual features of these organisms as beer spoilers is their Gram reaction and
obligately anaerobic status. Previously, the typical beer spoilers were regarded as being either lactic
acid bacteria or yeasts. Megasphaera and Selenomonas are best known as members of the rumen biota.
In addition to the organic acids noted above, Pectinatus spp. also produce H 2 S and acetoin. The beers
most susceptible to their growth are those that contain <4.4% alcohol.
With respect to spoiled packaged beer, one of the major contaminants found is Saccharomyces
diastaticus, which is able to utilize dextrins that normal brewers’ yeasts (S. “carlsbergensis” and
S. cerevisiae) cannot.
39 Pediococci, Flavobacterium proteus (formerly Obesumbacterium), and Brettanomyces are sometimes found in spoiled beer.
Wines
Wines are normal alcoholic fermentations of sound grapes followed by aging. A large number of
other fruits such as peaches, pears, and so forth may be fermented for wines, but in these instances the
wine is named by the fruit, such as peach wine, pear wine, and the like. Because fruits already contain
fermentable sugars, the use of exogenous sources of amylases is not necessary, as it is when grains
are used for beers or whiskeys. Wine making begins with the selection of suitable grapes, which are
crushed and then treated with a sulfite such as potassium metabisulfite to retard the growth of acetic
acid bacteria, wild yeasts, and molds. The pressed juice, called must, is inoculated with a suitable
wine strain of S. “ellipsoideus.” The fermentation is allowed to continue for 3–5 days at temperatures
between 70
◦ F and 90
◦ F (21
◦ C and 32
◦ C), and good yeast strains may produce up to 14–18% ethanol.
58
Following fermentation, the wine is racked–that is, drawn off from the lees or sediment, which contains
potassium bitartrate (cream of tartar). The clearing and development of flavor occur during the storage
and aging process. Red wines are made by initially fermenting the crushed grape must “on the skins”
during which pigment is extracted into the juice; white wines are prepared generally from the juice of
white grapes. Champagne, a sparkling wine made by a secondary fermentation of wine, is produced
by adding sugar, citric acid, and a champagne yeast starter to bottles of a previously prepared, selected
table wine. The bottles are corked, clamped, and stored horizontally at suitable temperatures for about
6 months. They are then removed, agitated, and aged for an additional period of up to 4 years. The
final sedimentation of yeast cells and tartrates is accelerated by reducing the temperature of the wine to
around 25
◦ C and holding for 1–2 weeks. Clarification of the champagne is brought about by working
the sediment down the bottle onto the cork over a period of 2–6 weeks by frequent rotation of the
bottle. Finally, the sediment is frozen and disgorged upon removal of the cork.
Table wines undergo spoilage by bacteria and yeasts with Candida valida being the most important
yeast. Growth of this organism occurs at the surface of wines, where a thin film is formed. The
organisms attack alcohol and other constituents from this layer and create an appearance that is
sometimes referred to as wine flowers. Among the bacteria that cause wine spoilage are members of
the genus Acetobacter, which oxidize alcohol to acetic acid (produce vinegar). The most serious and
the most common disease of table wines is referred to as tourne disease. Tourne disease is caused
by a facultative anaerobe or an anaerobe that utilizes sugars and seems to prefer conditions of low
alcohol content. This type of spoilage is characterized by an increased volatile acidity, a silky type
of cloudiness, and later in the course of spoilage, a “mousy” odor and taste caused by Brettanomyces
spp. commonly found in Bordeaux wines.
Malo-lactic fermentation is a spoilage condition of great importance in wines. Malic and tartaric acids are two of the predominant organic acids in grape must and wine, and in the malolactic