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Yeast need a reliable source of nitrogen in forms that they can assimilate in order to successfully complete fermentation. Yeast assimilable nitrogen or YAN is the combination of free amino nitrogen (FAN), ammonia (NH 3) and ammonium (NH 4 +) that is available for a yeast, e.g. the wine yeast Saccharomyces cerevisiae, to use during fermentation.
Microbial food cultures are live bacteria, yeasts or moulds used in food production. Microbial food cultures carry out the fermentation process in foodstuffs. Used by humans since the Neolithic period (around 10 000 years BC) [1] fermentation helps to preserve perishable foods and to improve their nutritional and organoleptic qualities (in this case, taste, sight, smell, touch).
Furthermore, the term culture is more generally used informally to refer to "selectively growing" a specific kind of microorganism in the lab. It is often essential to isolate a pure culture of microorganisms. A pure (or axenic) culture is a population of cells or multicellular organisms growing in the absence of other species or types.
Together with ammonia, FAN makes up the measurement of yeast assimilable nitrogen that can be measured prior to the start of fermentation. [1] The exact components of FAN will vary from the composition of the wort or grape must. In wine, all 21 amino acids can be found in trace amounts with arginine, proline and glutamine being the most abundant.
The count represents the number of colony forming units (cfu) per g (or per ml) of the sample. A TVC is achieved by plating serial tenfold dilutions of the sample until between 30 and 300 colonies can be counted on a single plate. The reported count is the number of colonies counted multiplied by the dilution used for the counted plate
Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity chemicals, such as acetic acid, citric acid, and ethanol are made by fermentation. [1]
The density of a wort is largely dependent on the sugar content of the wort. During alcohol fermentation, yeast converts sugars into carbon dioxide and alcohol. By monitoring the decline in SG over time the brewer obtains information about the health and progress of the fermentation and determines that it is complete when gravity stops declining.
A SCOBY used for brewing kombucha Kombucha co-culture with SCOBY biofilm. Symbiotic culture of bacteria and yeast (SCOBY) is a culinary symbiotic fermentation culture consisting of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast which arises in the preparation of sour foods and beverages such as kombucha. [1]