460 ENZYMES OF YEAST. 



five stages: (i) Washing the beer yeast; (2) Draining the 

 washed yeast ; (3) Mixing with quartz sand and kieselguhr ; 

 (4) Grinding to a pasty mass; (5) Pressing these two latter 

 stages being repeated. On account of their importance several 

 of these stages will now be described in greater detail. 



The washing of the brewery yeast was found to be an essential 

 feature. It is preferably performed in an apparatus designed by 

 HAGENMULLER (I.). Before mixing, the yeast must be well 

 drained to free it from water, for which purpose it is placed in a 

 stout, unstiffened cotton cloth (e.g., watertight tent canvas) and 

 pressed for five minutes under a pressure of 50 atmospheres. 

 The resulting yeast cakes, containing 70 per cent, of water, are 

 next mixed with fine quartz sand (passed through a sieve with 

 200 meshes to the sq. cm.) and kieselguhr or diatomaceous earth, 

 in the proportion of 1000 grms. of yeast to 1000 grms. of quartz 

 sand and 200-300 grms. of kieselguhr, the whole being sifted 

 through a coarse sieve (9 meshes per sq. cm.). The grinding is 

 effected in small quantities 300-400 grms. at a time either in 

 a mill or in a mortar with a loaded pestle provided with a pestle 

 guide, the operation being continued until a pasty mass is formed, 

 that " balls " and becomes detached from the walls of the mortar. 

 The pasty masses are united, placed in a damp press cloth, of the 

 type mentioned above, and subjected to a pressure, rising gradually 

 to 1280 Ib. per sq. inch, in a hand-operated hydraulic press. In 

 order to increase the yield, the press cakes are divided into small 

 portions and triturated over again in the mortar. At first, water 

 was added at this stage, but subsequently it was omitted as super- 

 fluous. The exuding yeast juice is allowed to trickle down on to a 

 folded filter, and thence into a vessel cooled with ice. 



The yield of expressed juice obtained by this method varies 

 between 450 and 500 c.c., so that after deduction of the cell 

 membrane about 60 per cent, of the total cell contents is 

 recovered. WROBLEWSKI (V.) obtained a yield of 72 percent.; 

 MACFADYEN, MORRIS and ROWLAND (I.), working with a pressure 

 of 200-350 atmospheres, obtained 5-87 per cent.; LANGE (II.) 

 with 15 per cent, of added water 44 per cent., and AHRENS (I.) 

 70 per cent. After this treatment the press cakes are not 

 exhausted, a further quantity of fermentative material being 

 recoverable by repeated trituration and pressing after a small 

 addition of water. Indeed, according to BUCHNER and RAPP (VII.), 

 these later fractions mostly exhibit a stronger fermentative power 

 than those from the first operation. WILL (XX.) also states that 

 the residual press cakes still contain considerable quantities of 

 zymase. Presumably the fermentative enzyme is dissolved by a 

 further addition of water. 



When the expressed yeast juice is properly prepared, only a 

 few unbroken yeast cells can be discovered in it under the micro- 

 scope ; but it may be stated at once that these cells are not capable 



