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Yeasts are unicellular micro-organisms that are used with some fermentation processes in the food industry, for example the production of bread and beer. In general, yeasts are converted into alcohol, water, carbonic acid and aromas during the fermentation process. With the production of bread the alcohol evaporates during the baking process.
The consumption of yeast differs widely around the world. In countries where rice is the primary food, no yeast is consumed. In Europe and the US each resident consumes 2 kg yeast per year.
The production process mentioned below gives a description of the production of bakery yeast. Bakery yeast consists of cells of the division Saccharomyces cerevisisiae.
Production process of yeast
Dissolving and settling
A basis with a high sugar content is necessary as raw material for the production of yeast. For this molasses is used. This is a by-product of sugar production. In the first place a suspension is made of the molasses with water. Afterwards the suspension is settled down: large particles are removed from the molasses so that a molasses solution is obtained.
The production of yeast is a fermentation process. When food is fermented it should not contain other micro-organisms. These micro-organisms would influence the growth of the desired micro-organisms (yeast). In this way, a competing flora may predominate so that no or little yeast is produced. The consequence is an impure yeast and a low efficiency. By sterilizing all vegetative micro-organisms and spores are killed so that no competing flora is present. Besides, it is important that all equipment that is used in the process is cleaned and sterilized before it is used, see also EHEDG
The sugar solution is cooled down to 33°C. This is the best growth temperature of the yeast.
To improve the growth aiding agents are added, for example nutritional salts and acids.
During this phase the graft of the division Saccharomyces cerevisisiae is also added. A graft consists of a very pure and concentrated mass of the desired division.
For several days the yeast is given time for multiple duplication. To make the growth as beneficial as possible the temperature is kept constantly at the right lvel. In order to grow the micro-organism requires oxygen. Therefore, sterile air is constantly brought into the solution. Yeasts can also survive anaerobic, but the growth will be negligible.
Sometimes extra nutrition, like sugar, is added during the fermentation process.
If the largest part of the sugars is consumed the yeast cannot properly duplicate itself. In order to prevent damage to the yeasts when harvesting the fermentation is ended. No more oxygen is added and the temperature is not regulated anymore. After the fermentation process the yeasts are separated from the solution by means of a centrifuge. The sugar free molasses is transported for further processing for the fodder industry. The mass with a high yeast content is purified.
Purification occurs by bringing the mass through a centrifuge several times. Again, the waste matter can be processed for the fodder industry. The purified yeast can be processed in such a way that it can be used as fresh yeast or as active dry yeast. Both processed are described below.
For the production of fresh yeast the yeast is first concentrated by means of a vacuum filter. The product is brought under a vacuum and past a filter. The filter has such small holes that the yeast cells cannot get through them. In this way, a large part of the water with the salts and acids is removed from the mass. A concentrated and relatively solid mass remains.
Cooling and pressing
The yeast mass is cooled and pressed. Due to the cooling process the consistency of the product increases. For the storage life of the product it has to be cooled down to 3°C at most in order to avoid the growth reinfection. During the pressing process, by means of extrusion
, the yeast cells are pressed in a block shape. The yeast blocks are produced in two different sizes.
The blocks are packed in waxed paper and stored at a temperature of 3°C at most. Fresh yeast has a storage life of a week if it is stored in a cool place.
Active dry yeast
In order to produce active dry yeast the yeast is concentrated by means of inverted osmosis, which is also called micro-filtration. By means of high pressure water with small dissolved salts is pressed through a filter. A concentrated yeast mass is left behind.
The concentrated yeast mass is dried by means of fluid bed drying. This means that a layer of the product is placed on a conveyor. Subsequently hot air is blown over the product. Because of the air blown through the product the mass does not remain a static layer but is moving. In this way grains of dry yeast are formed. This way of drying is chosen because the temperature is not very high during this process so that the yeast cells do not get damaged but remain active.
The dried yeast can possibly be stored in silos before it is packed. With fresh yeast interim stocking is almost impossible.
The dried grains of yeast are packed in synthetic foil bags. By packing with inert gas the storage life of the yeast grains is better guaranteed. Dried yeast has a storage life of several months.
Yeasts are unicellular micro-organisms that are used with some fermentation processes in the food industry, for example the production of bread and beer. In general, yeasts are converted into alcohol, water, carbonic acid and aromas during the... volle Beschreibung