Wild yeast

Primitive people very likely encountered vinegar-like Hquids in hoUows in rocks or downed timber into which berries or fmit had fallen. Wild yeasts and bacteria would convert the natural sugars to alcohol and acetic acid. Later, when eady peoples had learned to make wines and beers, they certainly would have found that these Hquids, unprotected from air, would turn to vinegar. One can postulate that such eady vinegars were frequendy sweet, because the fmit sugars would have been acted on simultaneously by both bacteria and yeast. Only since the middle 1800s has it been known that yeast and bacteria are the cause of fermentation and vinegar formation. 

Fermentations in larger vessels and the final trade fermentation are conducted under quasi-stetile conditions, and yeast growth is accompanied by some growth of contaminant bacteria. These are generally lactic acid-producing organisms but are sometimes coHform bacteria the occurrence of Salmonella in fermentor Hquids has not been reported. Massive contamination with Oidium lactis or wild yeasts has been reported. 

Beer taste can be spoiled by contaminating bacteria or yeasts. The most common bacteria are lactic and acetic acid producers and T ymomonas. Wild yeasts can be anything other than the intended strain S. uvarum is considered a contaminant of ale fermentations and S. cerevisiae a contaminant of lager fermentations. The common wild yeast contaminants are S. diastaticus and species of Picbia, Candida and Brettanomjces. It may be noted that the flavor of beer may be improved by the ability of yeast to adsorb bitter substances extracted from hops, such as humulones and isohumulones. 

Kaltguss, m. spoiled casting, kaltliammerbar, a. malleable, kalthkmmem, v.t. cold-hammer, cold-forge. Kalt-hefe,/. wild yeast, -lack, m. cold varnish. 

Wilde, m. /. savage wildness wilderness. Wildgeschmack, m. gamy taste, wildgewachsen, a. grown wild, rtm wild. Wild-hefe, /. wild yeast, -kirschenrinde, /. wild cherry bark, -leder, n. buckskin, deerskin chamois sudde. 

Presumably, at some point in history a batch of unleavened bread dough became contaminated with wild yeast and the first leavened bread was made. The only way in which such a system can be kept going is to keep back a portion of the old dough and add more flour and water to keep the fermentation going. In such a system various side-reactions occur and fatty acids start to be produced, hence the name. The acids give the dough some protection from contamination with undesirable moulds, which would be an advantage in a primitive society. 

If the culture is to provide both the yeast and the flavour of sour dough then either it must acquire a wild yeast or a starter culture that includes yeast must be added. In some cases the sour dough culture is only used to give the sour dough taste while conventional yeast is added. 

Haploid chromosome number, Wild yeast strains generally have eight (octoploid) or more sets of these chromosomes,... 

Pure Yeast Culture. Recheck population periodically for purity. If a wild yeast population builds up significantly, discard the culture and begin again from a slant. Some wineries are using mass pitching techniques with dry or frozen yeast very successfully. This eliminates the need for any monitoring of culture population. Wild yeasts often cause unreliable and erratic fermentation rates, and this is often accompanied by off odors and off flavors in the wine. Erratic fermentations also often invite bacterial contamination. 

Yeasts and Bacteria. One of the purposes of adding S02 is to inactivate bacteria and wild yeast so that the fermentation may be conducted with a chosen desirable strain of yeasts. Fortunately the wild yeast and the bacteria on grape berries (frequently confused in the older literature with the wax-like bloom which is naturally present on some berries) are susceptible to inactivation by relatively low doses of S02. A clear field is thus available to the large inoculum of S02-tolerant pure culture yeast added by the enologist. 

White Table Wines. The free-run grape juice is the most important fraction used in white table wine production. To the juice will be added S02 at 75-150 mg/L, depending on the grape condition. Most winemakers prefer to add not over 100 mg/L. The primary purpose of the S02 is to prevent browning and retard growth of wild yeasts and other undesirable microorganisms. 

Pure yeast starter at 2-4 percent volume level is added to the grape juice to initiate the fermentation sooner and to prevent wild yeasts from developing. 

Sulfurous acid inhibits molds and bacteria and to a lesser extent yeasts. For this reason, S02 can be used to control undesirable bacteria and wild yeast in fermentations without affecting the S02-tolerant cultured yeasts. According to Chichester and Tanner (1968), the undissociated acid is 1,000 times more active than HS03 for Escherichia coli, 100 to 500 times for Saccharomyces cerevisiae, and 100 times for Aspergillus niger. 

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