218 Dynamic Theory. 



Of the acetic acid there is, according to some, usually five per cent, 

 of the original quantity of the sugar, provided the fermentation is 

 stopped as soon as the sugar is all transformed. Otherwise the quantity 

 is increased, a part of the yeast itself, perhaps, being converted into the 

 acid. Other acids are also apt to result, as Lactic acid, but when that 

 happens it is due to another ferment which may get into the liquid from 

 the air. 



According to Pasteur, 100 parts of cane sugar, which corresponds to 105.26 parts of 

 grape sugar, yields in consequence of fermentation : 



Alcohol - 51.11 



Carbon Dioxide 49.42 



Succinic Acid - .67 



Glycerine 3.16 



Matter united with ferment - - .90 105.26 



The first operation which beer yeast performs on cane sugar is to " alter it " by separat- 

 ing it into two isomeric parts called glucose and levulose This is affected by the- 

 zymase accompanying the yeast. Of it we shall hear again. Cane sugar, or saccharose, 

 turns polarized light to the right. After alteration into the two parts, which are of equal 

 weight ; while they remain together the rotary polarization is to the left 25. The rotary- 

 twist in the glucose alone is to the right with a power expressed by +57.8, from which 

 it is also called dextrose. While the other sugar, called levulose, when alone has a left 

 polarization expressed by 106 (hence its name). (For Polarization, see Chap. 41 > 

 The chemical formula of these sugars is thus expressed: 



Saccharose. Water. Glucose. Levnlose. 



Ci 2 H 22 O n + H 2 O = C G H 12 O 6 + C 6 H 12 6 



The addition of the molecule of water to the molecule of saccharose, forms a molecule 

 composed of atoms, even in number, of each of the elements concerned, so that it is pos- 

 sible to split it into two parts, each containing the same elements in equal amount; Sac- 

 charose, after the water is added, having this formula: Ci 2 H 24 O 12 . When split the two- 

 resulting molecules have the same formula C 6 H 12 O 6 . The chemical analysis of these 

 two then would make them precisely alike. But when looked at through polarized light 

 they are proved to be mechanically different. 



This separation, or alteration, is necessary before the further disintegration into alco- 

 hol and carbon dioxide can be effected by the ferment. The alteration can, however,, 

 be accomplished by other means by simply boiling the carte sugar dissolved in water, 

 or by the use of acids, or by exposing it to the light, or even by the mere pulverizing of 

 the sugar. 



Glucose (grape sugar or starch sugar), levulose (same as the sugar of acid fruits), 

 maltose, or the sugar of malt formed by the action of diastase on dextrine, and lactose,. 

 or sugar derived from sugar of milk (lactine), by the action of acids; all have the same 

 formula: C H 12 O 6 . They all act almost exactly alike in the presence of the ferments- 

 splitting up into alcohol and carbon dioxide without undergoing any previous transform- 

 ation. " The rotary power of a solution of glucose diminishes in proportion to the quan- 

 tity of alcohol produced." 



" Glucose mixed with levulose ferments sooner than the latter does by itself." The 

 glucose disappears before the levulose, which last of all undergoes alcoholic decomposi- 

 tion, Dubrunfant has given this phenomenon the name of elective fermentation. The 

 sugars whose composition is represented by the same formula as cane sugar (Ci 2 H 22 O u ). 

 can be fermented only on condition of being first hydrated, that is, having a molecule 

 of water, H 2 O, added chemically to each molecule of sugar. This may be accomplished 

 as above stated, by an acid, or light, or water alone, or the action of the ferment. Glu- 

 cose crystallizes while levulose remains uncrystallizable. 



Meletizose, melitose and lactine, or sugar of milk, like cane sugar, must be hydrated 

 before fermentation can proceed. Only half of melitose "is decomposed into alcohol 

 and carbon dioxide, the other is transformed into a compound, isomeric with glucose ; 

 namely, eucalin, which is not fermentable." "All bodies capable of producing glucose 

 and its congeners by hydration, belong to the class of indirectly fermentable substances, 

 such as starch, dextrine, gum, glycogeae, and the various glucosides which are found 

 in vegetable tissues." ( Schiitzenberger, 33.) It is necessary that the ferment be in di- 

 rect and immediate contact with the elements to be fermented in order that the action 



