Adapted from Nout and Rombouts, 1992
Adapted from Nout and Rombouts, 1992
mally present at only about 103 cells per gram. Thus, the lactic acid bacteria are outnumbered by non-lactic competitors by a thousand times or more, putting them at a serious disadvantage.
Given the diversity of microorganisms initially present in the raw material and the numerical disparity between the lactic and non-lactic bacteria, it would seem that rather severe measures must be adopted to establish the selective environment necessary for a successful lactic acid fermentation. Actually, selection is based on only a few simple factors: salt, temperature, and anaerobiosis.Thus, under appropriate conditions, most non-lactic acid bacteria will grow slowly, if at all. In contrast, lactic acid bacteria will generally be unaffected (but not totally,), and will instead grow and produce acidic end products. The acids, along with CO2 that may also be produced, creates an even more stringent environment for would-be competi-tors.Within just a few hours, lactic acid bacteria will begin to grow, a lactic acid fermentation will commence, and the number of competing organisms will decline.
The lactic acid fermentation that occurs during most vegetable fermentations depends not on any single organism, but rather on a consortium of bacteria representing several different genera and species (Table 7-3). That is, a given organism (or group of organisms) initiates growth and becomes established for a particular period of time.Then, due to accumulation of toxic end products or to other inhibitory factors, growth of that organism will begin to slow down or cease. Eventually, the initial microbial population gives way to other species that are less sensitive to those inhibitory factors. Microbial ecologists refer to these sorts of processes as a succession.This is one reason why vegetable fermentations are ordinarily conducted without starter cultures, since duplicating a natural succession of organisms likely would not be achieved on a consistent basis.
Few fermented foods are produced in such a seemingly simple process as is sauerkraut (Figure 7-1). Only two ingredients, cabbage and salt, are necessary, and once these ingredients are properly mixed, there is little that the manufacturer needs to do until the fermentation is completed. The simplicity of the process is reflected by the U.S. Standards, which states that sauerkraut is the "product of characteristic acid flavor, obtained by the full fermentation, chiefly lactic, of properly prepared and shredded cabbage in the presence of not less than 2 percent nor more than 3 percent of salt."After fermentation, sauerkraut should contain not less than 1.5% acid (expressed as lactic acid).
The manufacture of sauerkraut starts with the selection of the raw substrate material. Although various cabbage cultivars exist, white cabbage is typically used because it has a mild, slightly sweet flavor and contains 5% or more fermentable sugars (mostly equimolar amounts of glucose and fructose, with a small amount of sucrose). Cabbage used to make sauerkraut should be fully mature, and should contain few outer leaves. Some manufacturers allow the cabbage heads to wilt for a day or two.
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