Yeast press juice

The arguments centering around Pasteur s ideas were settled finally in 1897, when Buchner prepared a cell-free extract of compressed yeast ( yeast press Juice ) that could carry out alcoholic... 

One of the outstanding achievements of biochemistry has been the elucidation of the sequence of chemical reactions and the isolation of the enz5nmes which are involved in the alcoholic fermentation of sugars by yeast. This story had its beginning in one of the historic experiments in plant science, the preparation of yeast press juice by Hans and Edward Buchner in 1897 and the demonstration that this juice could promote an active fermentation of sucrose. 

Fermentation of the press juice of Citrus unshuii Marcovitch by 125 strains of yeasts was conducted (15). Cell growth was near... 

Lee RK, Ryu HW, Oh H, Kim M, Wee YJ (2014) Cell-recycle continuous fermentation of Enterococcus faecalis RKYl for economical production of lactic acid by reduction of yeast extract supplementation. J Microbiol Biotechnol 24 661-666. doi 10.4014/jmb. 1402.02017 Leiss S, Venus J, Kamm B (2010) Fermentative production of L-Lysine-L-lactate with fractionated press juices from the green biorelinery. Chem Eng Technol 33(12) 2102-2105. doi 10. 1002/ceat.201000314... 

The intermediate steps of metabolism have been the subject of much discussion. Some aspects will be treated briefly below. Meyerhof (54) states that the glucose molecule passes anaerobically through twelve stable intermediary steps before forming alcohol and carbon dioxide at least three dissociable organic enzymes, twenty or more enzyme proteins and some bivalent metals (Mn and Mg) are necessary for the breakdown. This is a widely accepted conclusion from the work on fermentation by yeast extracts (press juice, maceration juice prepared from dried yeast, frozen yeast, or mechanically disrupted yeast) in which phosphoiylation is considered important in desmolysis. Decarboxylation of pyruvic acid appears to be the source of the carbon dioxide. Obviously then, carbon dioxide production is far from the initial step of permeation of glucose. 

In cold pressing pulp for white wines, present practices vary considerably within the industry. Some processors using continuous presses have found it an advantage to treat pulp with pectolytic enzymes prior to pressing. However, with the Willmes press, cold pulp to which cellulose fibers have been added press with no difficulty, and juice yields have been considered satisfactory. A general practice has been to add pectolytic enzymes to white must before yeast inoculation as an aid to rapid clarification of the new wine. 

If juice is to be sold as not from concentrate it is usually screened and pasteurised immediately after pressing - an operation with two main objectives. The first is to control the growth of spoilage micro-organisms that live on the fruit surface (mainly yeasts and moulds). The second is to destroy the pectolytic enzymes that occur naturally in fruit that would otherwise break down the cloudy nature of the juice. If, however, a clear juice is required (e.g. apple or raspberry), enzymes can be added to accelerate this natural process. 

Soft drinks, or to quote their early designation, mineral waters or table waters , appeared as a commercial prospect in the mid-eighteenth century. Consequently, their development towards full-scale production followed hot on the heels of the Industrial Revolution taking place at that time throughout Europe and the Western world. Prior to this, although freshly pressed or squeezed juices were available for direct consumption to comply with the description soft drink , these were inherently unstable if stored, quickly succumbing to yeast attack and resulting fermentation. 

Subsequent yeast and lactic bacteria metabolism in the press-run juice occurs in a medium rich in sugars and with a high potential for microbial growth (Barre, 1969). This helps explain the speed of the second fermentation phase, the early "biologic stability" of the wines, and the possible yeast and bacterial competition. 

For white wine production, the grapes usually were not stemmed. The crushed grapes were left for six to ten hours before the free-run (separated) juice was drawn off. The pomace was then pressed and the pressed pomace was washed as with red pomace. The fermentation of white musts was done in 2/3-full oak casks. The fermentation was watched daily. The yeast foam was removed. By the sixth day, the fermentation had slowed down sufficiently to then use a fermenting bung. The Italians often use a bag of sand, which they place over the bung-hole. He recommended fermenting room temperatures of 21°-27° C and cellar temperatures of 15.6°-21° C, preferring 15.6° C after the first year. 

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