ALBUMINUI I ) Ml LlNUls Si liSTANCJ^ i fi^ 



The cliit'f practical difTerence between top ferineiit«tion and 

 bottom I'ermoiitiitiuii is due to the afuresaid ri-latiou iK'tween 

 the yeast cells aud the mucinous substances, either protluceti iu 

 the nutrient medium or excreted by the cells themselves. A 

 typical example uf top-fermentiitiun yeast in its fullest de- 

 velopment is alVorded by the stocks forming the chief comj>oneut 

 of unadultei-ated pressed yeast. The main features in the 

 preparation of this article by the old or Viennese metiiod are 

 as follow : Alnjut three to four hours after the wort has Ijeen 

 pitched with yeast — a so-called "lUtilicial " yeast (§ 148) of 

 suitiible ijuality — the mash begins to work. The scum of husks 

 and grains that has accumulated on the surface in the mean- 

 time, is now penetnited liy an ascending white head, the 

 development and growth of which, during the next twelve 

 hours, presents a picture of eViullient motion of ci>nsideiiil)le 

 briskness. Under ordinary circumstunces the head at the end 

 of this time will have attained a thickness of twelve to fifteen 

 inches, whilst the gravity of the wort will have decreased to about 

 half its initial value. This head foriiis the vehicle containing 

 the major part of the yeast crop repro<luced from the pitching 

 yeast. The buljbles are still ti-anspareut. Whereas, during 

 the next three to four hours, the hea<l does not increase in 

 thickness to any great extent, the young cells therein begin to 

 grow ; this stage is termed the ripening of the head. The 

 bubbles beuiii to turn cloud v, and tinallv reveal the presence 

 of large yeast colonies which, to the unassi.sted eye, appear as 

 \vhit<? spots. The reproduction of the cells is now ended; the 

 vat is ripe, to u.se a pnictical term ; and the gravity of the wort 

 has fallen t*) about one-third the original stieiigth. The head 

 is next .skimmed olY by means of suittible skimmers, and is 

 tnvnsferred to a sifter in ortlei* to separate the coarser adherent 

 particles of the giiiin.s, the elimination of the finer \indesiruble 

 a<lmixtures being elTected by the subsequent washing, to which 

 reference will be made in the jiaragraphs dealing with the 

 aut<xligestion of yeast. For the present we will merely utter 

 a warning against a one-sided judgment and imperfect apprecia- 

 tion of the importance of the mucinous excretions in connection 

 with facilitating the a.scent of the veast in the fermentation 

 vats during the manufacture of pres.sed yeast, by citlling atten- 

 tion to the induence exeirised by the viscosity and chemical 

 constitution ui the mash on the working of the yeu>t., and 

 therefore on the yeast crt>p. More detJiiltnl information on this 

 matter will be found in the volume on pressed-yeast manufac- 

 ture, issued by O. Dlkst (I.). 



The so-calleil rit)t«.>us or blaildery fermentation of beer yeast 

 may be left out of consideration here. The sti-uctur.il mat<Mial8 

 for the large, tough bladders forming the head in thi- re 



not supplied by the yeast but from the sludge — iiJ» \".- .-.-wn 



