Yeast

Description

"Yeast" is a collective term for a group of microorganisms known as "sac fung"” and which reproduce by the use of spores.

Wild yeasts are widespread in nature. They colonise fruits and berries, for example, but also are known as sources of rot. Cultured yeasts are applied under controlled conditions in the production of food products and beverages. They are bred to display specific qualities (pure culture yeasts).

In the absence of air, yeasts initiate the process of fermentation. Enzymes produced by the yeasts split plant starches into alcohol (ethanol) and carbon dioxide. In the presence of sufficient oxygen, this does not occur. Yeasts then utilise starch for their own reproduction and no alcohol is produced.

Yeasts from the genus Saccharomyces display high degrees of fermentation ability and therefore are used in a variety of food products and beverages in order to refine or conserve them.

Application

Yeasts are used in brewing (beer yeast), in the production of wine- and spirits (wine yeast, distillers' yeast) and in baking (bakers' yeast).

• Bakers' yeast (Saccharomyces cerevisae) may be found on the market as compressed yeast or dry yeast. It is activated with nutrient solutions containing sugar.
• With regard to brewers' yeasts (Saccharomyces cerevisae and Saccharomyces carlsbergensis) a distinction is made between "top-" and "bottom-fermenting" yeasts.
• Wine yeast (Saccharomyces ellipsoides) is also found under natural conditions but is applied today almost exclusively as a pure cultivated yeast.
• Yeast also is available as dry yeast and is a source ofyeast extract and nutritional yeast.
• Yeast dregs, for example as obtained in breweries, broadly are used as animal feed.

Gene technology

Yeast is intensively processed with gene technology. As a rule, genetically modified yeast may be found in all levels of development and experimentation. Goals may include the following:

• Bakers' yeast: reduction of rising times for dough; improvement of dough stability
• Beer yeast: simplication of the process of fermentation for beers with reduced quantities of alcohol or calories; stability of taste; reduction of lees during filtering
• Wine yeast: optimisation of the process of fermentation, reduction in the length of fermentation times; stability or improvement of taste; enhancement of fermentation performance, aimed at the complete fermentation of sugar and the elimination of sweetness in wine; reduction of the fermentation of Champagne in the bottle; reduction of carcinogenic materials that arise during fermentation.

Permission: in the United Kingdom, two genetically modified yeasts were approved a few years ago: a bakers' yeast that displays a shorter rising time and a brewers' yeast that is used in diet beer. Neither yeast is used commercially on a large scale. No applications necessary for approval in the EU or in other countries have been submitted. To date, genetically modified yeasts are not present on the market in EU countries.

In the USA and Canada GM yeasts have been approved for primary use in the production of wine.

• A GM yeast (ML01) is used to improve the taste and colour stability of wine as well as to avoid the production of undesirable compounds (histamines). The yeast is approved also in Moldova.
• A GM yeast has been developed in Canada in the hope of reducing the presence of a specific compound (ethylcarbamate) that occurs naturally during fermentation and which is suspected to have carcinogenic effects. In the USA its use is recognized as safe (GRAS, Generally Recognized As Safe).
  (further information: wine)

Yeasts as producer organisms: genetically modified yeasts long have been in use in the production of medications, special chemical compounds, enzymes and food additives. The GM yeasts are maintained in closed systems (fermenters). The products that are manufactured in this manner are purified and are indistinguishable from equivalent compounds produced in the conventional manner.

Nutrient solutions for the cultivation of yeast: applications of gene technology are possibly to be found among the nutrient solutions that are applied in the cultivation and propagation of yeast.

• Nutrient solutions for yeasts: glucose, sugar or molasses, whey.

Labelling: foods that contain genetically modified yeasts or are produced therefrom are subject to labelling.

Products such as beer or wine that are produced with the aid of GM yeasts are not subject to labelling, provided that the yeasts in question fully have been removed from the product and are no longer detectable.

Yeast products or foods are not subject to labelling if the nutrient solutions used in the breeding and cultivation of the yeasts in question were won from genetically modified plants.