Nondairy Fermented Foods and Products
185
fermentation, contaminating bacteria degrade malic acid to lactic acid and CO 2 :
L(−)-Malic acid
“malo-lactic enzyme”
− −−−−−−−−−− → L(+)-Lactic acid + CO 2
l-Malic acid may be decarboxylated also to yield pyruvic acid.
41 The effect of these conversions
is to reduce the acid content and affect flavor. The malo-lactic fermentation (which may also occur
in cider) can be carried out by many lactic acid bacteria, including leuconostocs, pediococci, and
lactobacilli.
63 Although the function of the malolactic fermentation to the fermenting organism is not
well understood, it has been shown that Oenococcus oeni is actually stimulated by the process.
60 The
decomposition in wines of tartaric acid is undesirable also, and this process can be achieved by some
strains of Lactobacillus plantarum in the following general manner:
Tartaric acid −→ Lactic acid + Acetic acid + CO 2
The effect is to reduce the acidity of wine. Unlike the malo-lactic fermentation, few lactic acid bacteria
break down tartaric acid. Sluggish or stuck alcoholic fermentations of wines is caused by Lactobacillus
kunkeei and L. nagelii.
The bacterium Oenococcus oeni is an acidophile that can grow in grape must and wine at pH 3.5–
3.8, and actually prefers an initial growth pH of 4.8.
22 It can grow in the presence of 10% ethanol but
requires special growth factors found in grape or tomato juice. For a review, see reference 44.
Cider
Cider, in the United States, is a product that represents a mild fermentation of apple juice by
naturally occurring yeasts. In making apple cider, the fruits are selected, washed, and ground into a
pulp. The pulp “cheeses” are pressed to release the juice. The juice is strained and placed in a storage
tank, where sedimentation of particulate matter occurs, usually for 12–36 hours or several days if the
temperature is kept at 40
◦ F (4.4
◦ C) or below. The clarified juice is cider. If pasteurization is desired, this
is accomplished by heating at 170
◦ F (76.7
◦ C) for 10 minutes. The chemical preservative most often
used is sodium sorbate at a level of 0.10%. Preservation may also be effected by chilling or freezing.
The finished product contains small amounts of ethanol in addition to acetaldehyde. The holding of
nonpasteurized or unpreserved cider at suitable temperatures invariably leads to the development of
cider vinegar, which indicates the presence of acetic acid bacteria in these products. The pathway
employed by acetic acid bacteria is summarized in Chapter 7, Figure 7–1F, G.
In their study of the ecology of the acetic acid bacteria in cider manufacture, Passmore and Carr
53
found six species of Acetobacter and noted that those that display a preference for sugars tend to be
found early in the cider process, whereas those that are more acid tolerant and capable of oxidizing
alcohols appear after the yeasts have converted most of the sugars to ethanol. Zymomonas spp., Gramnegative bacteria that ferment glucose to ethanol, have been isolated from ciders, but they are presumed
to be present in low numbers. Saccharobacter fermentatus is similar to Zymomonas in that it ferments
glucose to ethanol and CO 2 .
92 It was isolated from agave leaf juice, but its presence and possible role
in spoiled ciders have yet to be determined. Zymobacter palmae is an ethanol fermentor isolated from
palm sap.
51 It produces ethanol from mannitol.
37
Following several illness outbreaks traced to apple cider, the microbial load of finished ciders
produced in the state of Iowa was investigated, and in apples from 21 producers, APC ranged from
15 to > 1.1 × 10
5 /ml; coliforms from <1 to 2.1 × 10
3 ; and E. coli was <10/ml.
18 The fate of E. coli
0157:H7 in fermenting apple cider was studied by Semanchek and Golden
75 who found that 6.4 log 10
cfu/ml of this organism were reduced to <0.5 log 10 cfu/ml after 3 days at 20
◦ C, while in nonfermenting
185
fermentation, contaminating bacteria degrade malic acid to lactic acid and CO 2 :
L(−)-Malic acid
“malo-lactic enzyme”
− −−−−−−−−−− → L(+)-Lactic acid + CO 2
l-Malic acid may be decarboxylated also to yield pyruvic acid.
41 The effect of these conversions
is to reduce the acid content and affect flavor. The malo-lactic fermentation (which may also occur
in cider) can be carried out by many lactic acid bacteria, including leuconostocs, pediococci, and
lactobacilli.
63 Although the function of the malolactic fermentation to the fermenting organism is not
well understood, it has been shown that Oenococcus oeni is actually stimulated by the process.
60 The
decomposition in wines of tartaric acid is undesirable also, and this process can be achieved by some
strains of Lactobacillus plantarum in the following general manner:
Tartaric acid −→ Lactic acid + Acetic acid + CO 2
The effect is to reduce the acidity of wine. Unlike the malo-lactic fermentation, few lactic acid bacteria
break down tartaric acid. Sluggish or stuck alcoholic fermentations of wines is caused by Lactobacillus
kunkeei and L. nagelii.
The bacterium Oenococcus oeni is an acidophile that can grow in grape must and wine at pH 3.5–
3.8, and actually prefers an initial growth pH of 4.8.
22 It can grow in the presence of 10% ethanol but
requires special growth factors found in grape or tomato juice. For a review, see reference 44.
Cider
Cider, in the United States, is a product that represents a mild fermentation of apple juice by
naturally occurring yeasts. In making apple cider, the fruits are selected, washed, and ground into a
pulp. The pulp “cheeses” are pressed to release the juice. The juice is strained and placed in a storage
tank, where sedimentation of particulate matter occurs, usually for 12–36 hours or several days if the
temperature is kept at 40
◦ F (4.4
◦ C) or below. The clarified juice is cider. If pasteurization is desired, this
is accomplished by heating at 170
◦ F (76.7
◦ C) for 10 minutes. The chemical preservative most often
used is sodium sorbate at a level of 0.10%. Preservation may also be effected by chilling or freezing.
The finished product contains small amounts of ethanol in addition to acetaldehyde. The holding of
nonpasteurized or unpreserved cider at suitable temperatures invariably leads to the development of
cider vinegar, which indicates the presence of acetic acid bacteria in these products. The pathway
employed by acetic acid bacteria is summarized in Chapter 7, Figure 7–1F, G.
In their study of the ecology of the acetic acid bacteria in cider manufacture, Passmore and Carr
53
found six species of Acetobacter and noted that those that display a preference for sugars tend to be
found early in the cider process, whereas those that are more acid tolerant and capable of oxidizing
alcohols appear after the yeasts have converted most of the sugars to ethanol. Zymomonas spp., Gramnegative bacteria that ferment glucose to ethanol, have been isolated from ciders, but they are presumed
to be present in low numbers. Saccharobacter fermentatus is similar to Zymomonas in that it ferments
glucose to ethanol and CO 2 .
92 It was isolated from agave leaf juice, but its presence and possible role
in spoiled ciders have yet to be determined. Zymobacter palmae is an ethanol fermentor isolated from
palm sap.
51 It produces ethanol from mannitol.
37
Following several illness outbreaks traced to apple cider, the microbial load of finished ciders
produced in the state of Iowa was investigated, and in apples from 21 producers, APC ranged from
15 to > 1.1 × 10
5 /ml; coliforms from <1 to 2.1 × 10
3 ; and E. coli was <10/ml.
18 The fate of E. coli
0157:H7 in fermenting apple cider was studied by Semanchek and Golden
75 who found that 6.4 log 10
cfu/ml of this organism were reduced to <0.5 log 10 cfu/ml after 3 days at 20
◦ C, while in nonfermenting