PRESERVING VEGETABLES AM) FRUIT 169 



are crushed, passes into the juice arid causes it to coagulate. This phenomenon 

 was explained by Frerny, in 1840, to be due to the action of an enzyme, viz., 

 pectase, whereby the pectin is converted into pectic acid. This opinion was 

 modified by the researches of G. BERTRAND and A. MALL^VRE (I.), in so far that 

 they showed that the enzyme can accomplish the transformation referred to only 

 when in presence of soluble silts of the alkaline earths (e.g. lime), with which 

 the pectic acid enters into combination, and forms insoluble pectates. The 

 presence of this gelatinising compound is indispensable for the preparation of 

 pure fruit jellies ; and the latter must not be too strongly boiled, or their setting 

 properties will be diminished or completely destroyed. In the preparation of fruit 

 juices, such as raspberry juice, it is necessary, on the other hand, to get rid of 

 these pectin substances, because they detract from the utility of the juice, which 

 should remain liquid. This end is attained by leaving the fresh juice to itself 

 for a time, fermentation soon ensuing, by which the pectin or pectate is 

 decomposed. The juice is then strained and boiled down after the addition of 

 sugar. A few references to the literature of the subject will be useful to the 

 food-stuft' chemist, who is not infrequently asked for advice concerning the best 

 means of turning fruit to account. Full particulars on the treatment of fruit in 

 general, as also of drying and preserving it, will be found in the handbooks of 

 FR. LUCAS (I.), KARL BACH (I.), and H. TIMM (I.). A brief introduction to the 

 preparation and treatment of fruit wines has been arranged by M. BARTH (I.), 

 and a pamphlet written by W. TENSI (I.) deals chiefly with currant wine (as the 

 finest of all fruit wines), as well as with gooseberry wine, &c. 



The preservation of wine-must is practised on a large scale, particularly in 

 Sicily. To render the juice highly suitable for transport, it is (after a preliminary 

 filtration) concentrated in vacua at 40 C. to about one-fourth of its original 

 volume. In this manner a thick, syrupy mass is obtained, the composition of 

 which can be deduced from the following analytical figures furnished by TH. 

 OMEIS : 



Water . . . . . . . . 35. i per cent. 



Dextrose + levulose 62.2 



Acid . . . . . . . 1.2 ., 



Ash. ... ..... 0.7 



Albumen, gum, &c 0.8 



This concentrated wine-must, which is shipped in sealed tins, is not in any 

 case sterile, though the still living germs (particularly yeasts) present therein 

 are, by reason of the high concentration of the liquid, incapable of development. 

 If, however, the mass be diluted with sterilised water, then fermentation ensues 

 within a short time. According to the experience of J. WORTMANN (II.), and 

 also of the author himself, the employment of this must can be recommended in 

 laboratories dealing with Fermentation Physiology. The dilution of i part of 

 must with 4 parts of water yields a nutrient medium exceedingly favourable for 

 the cultivation of higher fungi (wine yeasts), the low percentage of nitrogen 

 being improved by an addition of i per cent, of ammonium tartrate. 



The preservation of beer and wine by heating (Pasteurisation) will be dealt 

 with in a subsequent section of the second volume. 



