FERMENTATION 339 



PBRMBUTTATION 1 . (Fermentation, Fr.; Gahrung, Ger.) A change which 

 takes place, under the influences of air and moisture at a certain temperature, in the 

 constituent particles of either vegetable or animal substances. This change is in- 

 dicated by a sensible internal motion the development of heat the evolution of 

 gaseous products. Fermentation may be divided into several kinds, as 



Saccharine, Butyric, 



Acetic, Glyceric, 



Alcoholic or Vinous, Lactic, 



Putrefactive, Mucous. 



Of the latter examples but a brief notice is required. Mucous fermentation is esta- 

 blished when the juice of the beetroot or carrot is kept at a temperature of 100 for 

 some time, when a tumultuous decomposition takes place. All the sugar disappears, 

 and the liquor is found to contain a large quantity of gum, and of mannite with lactic 

 acid. 



Lactic Fermentation. If a solution of one part of sugar in five parts of water be 

 made to ferment, by the addition of a small quantity of cheese or animal membrane, 

 at a temperature of 90 or 100, lactic acid is formed, which may be separated by 

 adding a little chalk, the lactate of lime depositing in crystalline grains. In lactic 

 fermentation mannite invariably is produced as a secondary product, the formation of 

 which is not explained. It has been suggested that the formation of mannite is con- 

 nected with the production of succinic acid, which Schmidt, in a letter to Liebig, stated 

 that he had found in fermenting liquids containing sugar. He suggested the following 

 equation (Schmidt's formulae are retained) : 



C 8 H 9 8 + C 4 H 3 0* = C 12 H 12 12 



Mannite. Succinic acid. Grape sugar. 



Glyceric Fermentation. When glycerine is mixed with yeast, and kept in a warm 

 place for some weeks, it is decomposed and converted into metacetonic add. This 

 fermentation resembles the last named. The glycerine, C 6 H 7 5 , forming metacetonic 

 acid, OIPO 4 , as sugar, C 6 H 6 0", does lactic acid, C 8 H 5 5 , by loss of the elements of 

 water. Kane. 



Butyric Fermentation. If the lactic fermentation is allowed to proceed beyond the 

 point indicated for the formation of lactate of lime, the precipitate in part redissolves 

 with a very copious evolution of hydrogen gas and carbonic acid, and the liquor con- 

 tains butyrate of lime. In this action two atoms of lactic acid, C 12 H 10 10 , produce 

 butyric acid, C 8 H 7 3 , carbonic acid, and hydrogen gas. 



Putrefactive Fermentation. See PUTREFACTION. 



The three first-named kinds of fermentation demand a more especial attention from 

 their importance as processes of manufacture. Under the heads respectively of ACETIC 

 ACID, BEER, BREWING, DISTILLATION, MALT, and WINE, will be found everything con- 

 nected with the practical part of the subject ; we have therefore only now to deal with 

 the chemical and physical phenomena which are involved in the remarkable changes 

 which take place. When vegetable substances are in contact with air and moisture, 

 they undergo a peculiar change (decomposition). Oxygen is absorbed and carbonic 

 acid and water are given off, while there is a considerable development of heat. This 

 may take place with greater or less rapidity, and thus eremacausis, fermentation, or 

 combustion, may be the result ; the spontaneous ignition of hay (as an example) being 

 the final action of this absorption of oxygen. 



Saccharine Fermentation. If starch, C 12 H 9 9 + 2HO, be moistened with an infusion 

 of pale malt, it is rapidly converted into dextrine, C 12 H 10 10 , and hence into grape 

 sugar, C 12 H 12 12 ; this is especially called the saccharine fermentation, since sugar is 

 the result. 



Acetic and Alcoholic Fermentation. If sugar is dissolved in water, it will remain 

 perfectly unaltered if the air is excluded ; but if exposed to the air, a gradual decom- 

 position is brought about, and the solution becomes brown and sour. Oxygen has 

 been absorbed, and acetic acid produced. If, however, the sugar is brought into con- 

 tact with any organic body which is in this state of change, the particles of the sugar 

 participate in the process, carbonic acid is evolved, and alcohol produced. There are 

 some substances which are more active than others in producing this change. Yeast 

 is the most remarkable ; but blood, white-of-egg, glue, and flesh, if they have begun 

 to putrefy, are capable of exciting fermentation ; vegetable albumen and gluten being, 

 however, more active. Vegetable albumen, gluten, and legumin differ from most 

 vegetable bodies in the large quantity of nitrogen which they contain. These sub- 

 stances exist in all fruits ; and hence, when fruit is crushed, the sugar of the juices in 

 contact with the albumen or gluten being then exposed to the air, oxygen is rapidly 



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