Nitrogen fermentation

Regulations specify a considerable Hst of additives and treatments which may be permitted under controlled limits and conditions. It is important to note that no wine receives mote than a few of these treatments, and many have none. For example, most grape musts ferment readily without additions, but some extra nitrogen source for the yeasts is occasionally beneficial. If some is requited, ammonium phosphate is the most commonly used. 

Grape and apple juices usually contain all of the trace nutrients required by Saccharomjces for fermentation of sugars to alcohol. Other fmit and diluted honey, as well as barley malt and rice extract, frequendy need additions of nitrogen, phosphoms, and potassium compounds, together with some autolyzed yeast to faciUtate the yeast growth necessary for fermentation. Stimulation oiy4.cetobacter frequendy requires the addition of autolyzed... 

Saccharomyces yeasts are rapid fermentors. S. cerevisiae and S. bayanus produce up to 18—20% ethanol. The cells are ovoid to spherical, eUiptical, or elongated (especially under conditions of nitrogen starvation). Vegetative propagation is by multilateral budding. S. uvarum and S. rosei occur earher in the fermentation, when S. rosei may produce up to 6—8% ethanol before being overgrown by the other Saccharomyces yeasts. S. cerevisiae may produce up to 18-20% ethanol (28). 

Beet juice contains about 80% of fermentable carbohydrates and nitrogenous compounds. To remove these compounds, a yeast fermentation utilising Candida utillis has been suggested (141). By so doiag, a more concentrated form of the dye becomes available. The red dye from beets is sold as beet juice concentrate, as dehydrated beet root, and as a dried powder. 

If the yeast does not get enough free amino nitrogen, the fermentation will be poor and the beer quaHty inferior. A neutral bacterial protease added at mashing-in can be used to raise the level of free amino nitrogen. This is useful when working with poorly modified malt or with high adjunct ratios. 

A suitable fermentation medium contains water and a source of assimilable carbon and nitrogen and essential mineral salts. A typical medium suitable for production of chlorodemethyltetracycline is as follows ... 

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