Nov. 7, 1884.] 



♦ KNOWLEDGE ♦ 



375 



AN ILLUSTRATED '^ JO 



IAGAZINEofSCIENCE 

 ©^EfWORDED-ExACTiy Described 



LONDON: FRIDAY, SOY. 7, 1884. 



Contents op No. 158. 



PAOB 



The Chemistry of Cookery. XLVI. 



By W. Matfieu WiUiams 375 ' 



Fertilisation of Broad Beans, By ' 



Grant Allen 37B I 



Chapters on Modem Domestic 



Economy. I. Introduction 377 



Other Worlds than Ours. By Jt. 



de Fontenelle. With Notes br 



Richard A. Proctor ..,.". 377 



The Entomology of a Pond. (lUut.) 



By E. A. Butler 378 



French Balloon Experiments. By 



K. A. Proctor 380 



Electroplating. By W. Slingo 330 



Chats aDOUt Geometrical Measure- 

 ment. By R. A. Proctor 361 



Graphical Projection of an Eclipse 



of the Moon 363 



The Fish River Caves, near Sydney, 



Australia. (Illut.) 381 



Dickens's Story Left Half Told. 



By Thomas Foster 3SS 



Reviews 388 



Face of the Sky. By F.E.A.S 389 



Correspondence 390 



OoT Cheas Coltunn 394 



THE CHEMISTRY OF COOKERY. 



By W. Mattied Williams. 



XLVI.— THE COOKERY OF WINE-DRYING. 



THE reader •will understand, from what has already been 

 stated concerning the origin of the difference 

 between natural sweet wines and natural dry wines, that 

 the conversion of either one into the other is not a diffi- 

 cult problem. Wine is a fashionable beverage in this 

 country, and fashions fluctuate. These fluctuations are not 

 accompanied with a corresponding variation in the chemical 

 composition of any particular class of grapes, but somehow 

 the wine produced therefrom obeys the laws of supply and 

 demand. For some years past the demand for dry sherry 

 has dominated in this country, though, :is I am informed, 

 the weathercock of fashion is now on the turn. 



One mode of satisfying this demand for dry wine is, of 

 course, to select a grape which has less sugar and more 

 albuminous matter, but in a given district this is not always 

 possible. Another is to gather the grapes before they are 

 fully ripened, but this involves a sacrifice in the yield of 

 alcohol, and probably of flavour. Another method, obvious 

 enough to the chemist, is to add as much albuminous or 

 nitrogenous material as shall continue to feed the yeast 

 fungus until all, or nearly all, the sugar in the grape shall 

 be converted into alcohol, thus supplying strength and 

 dryness (or salinity) simultaneously. Should these be 

 excessive, the remedy is simple and cheap wherever water 

 abounds. It should be noted that the quantity of sugar 

 naturally contained in the ripe grape varies from 10 to 30 

 per cent. — a very large range. The quantity of alcohol 

 varies proportionally when the must is fermented to dry- 

 ness. According to Pavy, " there are dry sherries to Ise 

 met with that are free from sugar," whDe in other wines 

 the quantity of remaining sugar amounts to as much as 20 

 per cent. 



White of egg and gelatine are the most easily available 

 and innocent forms of nitrogenous material that may be 

 used for sustaining or renewing the fermentation of wines 

 that are to be artificially dried. My inquiries in the 

 trade lead me to conclude that this is not understood as 



well as it should be. Both white of egg and gelatine (in 

 the form of isinglass or otherwise) are freely used for fining, 

 and it is well enough known that wines that have been 

 freely sulijected to such fining keep better and become drier 

 with age, but I have never yet met a wine-merchant who 

 understood why, nor any sound explanation of the fact in 

 the trade literature.* When thus added to the wine 

 already fermented, the effect is doubtless due to the pro- 

 motion of a slow, secondary fermentation. The bulk of 

 the gelatine or albumen is carried down with the sediment, 

 but some remains in solution. There may be some doubt 

 as to the albumen thus remaining, but none concerning the 

 gelatine, which is freely soluble both in water and alcohol. 

 The truly scientific mode of applying this principle would 

 be to add the nitrogenous material to the must. 



I dwell thus upon this because, if fashion insists so im- 

 peratively upon dryness as to compel artificial drying, this 

 method is the least objectionable, being a close imitation of 

 natural drying, almost identical ; while there are other 

 methods of inducing fictitious dryness that are mischievous 

 adulterations. 



Generally described, these consist in producing an imita- 

 tion of the natural salinity of the dry wine by the addition 

 of factitious salts and fortifying with alcohol. The sugar 

 remains, but is disguised thereby. It was a wine thus 

 treated that first brought the subject of the sulphates, 

 already referred to, under my notice. This, although sold 

 to my friend at a good price, was a concoction of the 

 character known in the trade as Hambro' sherry. It con- 

 tained a considerable quantity of sugar, but was not per- 

 ceptibly sweet. It was very strong and decidedly acid; 

 contained free sulphuric acid and alum, which, as all who 

 have tasted it know, gives a peculiar sense of dryness to 

 the palate. 



The sulphuring, plastering, and use of Spanish earth, 

 described in my last, increase the dryness of a given wine 

 by adding mineral acid and mineral salts. In a paper 

 recently read before the French Academy by L. Magnier 

 de la Source (" Comptes-Rendus," vol. 98, page 110), the 

 author states that "plastering modifies the chemical cha- 

 racters of the colouring matter of the wine, and not only 

 does the calcium sulphate decompose the potassium hydrogen 

 tartrate, with formation of calcium tartrate, potassium sul- 

 phate, and free tartaric acid, but it also decomposes the 

 neutral organic compounds of potassium which exist in the 

 juice of the grape." I quote from abstract in Journalofthe 

 Chemical Society of May, 1884. 



In the French Journal of Pharmciceutical Chemistry, 

 vol. 6, pp. 118-123 (1882), is another paper, by P. Carles, in 

 which the chemical and hygienic results of plastering are 

 discussed. His general conclusion is that the use of gypsum 

 in clearing wines " renders them hurtful as beverages:" 

 that the gypsum acts " on the potassium bitartrate in the 

 juice of the grape, forming calcium tartrate, tartaric acid, 

 and potassium sulphate, a large proportion of the last two 

 bodies remaining in the wine." Unplastered wines contain 

 about two grammes of free acid per litre ; after plastering, 

 they contain " double or treble that amount, and even 

 more." 



A German chemist, Griessmayer, and, more recently, 

 another. Kaiser, have also studied this subject, and arrive 

 at similar conclusions. Kaiser analysed wines which were 

 plastered by adding gypsum to the must, that is to the 

 juice before fermentation, and also samples in which the 

 gypsum was added to the "finished wine," ie., for fining, 

 so called. He found that " in the finished wine, by the 



* The wine trade has two rival magazines, both very high priced, 

 exclnsively devoted to its interests, besides others that are partially 



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