LOSS OF COLOUR IN WINE. 315 



species of bacteria which convert the sugar of the must into mannite. 

 Of this hexatomic alcohol there will be produced, according to 

 circumstances, from i to 30 grams per litre of wine, in addition to 

 a little acetic acid. A knowledge of this fact is useful to the ana- 

 lytical chemist as well. Attention was first drawn to the mannite 

 content, of Algerian wines in particular, by P. CARLES (II.) in 

 1891. Figs, as is well known, very often contain considerable 

 quantities of this alcohol ; hence Carles thought that the presence 

 of mannite in any wine indicated adulteration by fig- wine. How- 

 ever, as reported by J. BEHRENS (IV.), the presence of mannite in 

 reliably pure natural wines (e.g. Bordeaux, Chateau- Yqu^m) had 

 been proved a year previously by Fortes and Laf auric ; and very 

 soon afterwards JEGON (I.) showed that in wines of reliable purity, 

 but imperfectly fermented, as much as eight grams of mannite 

 could be found per litre. L. Roos (I.) then proved that this result 

 was due to bacterial activity, a discovery confirmed by U. GAYON 

 and E. DUJBOURG (I.), who isolated from such wine a pure culture 

 of a non-motile short-rod fission fungus, capable of converting 

 sugar into mannite (up to 50 grams per litre). In nutrient 

 solutions devoid of sugar this species fails to develop, a circum- 

 stance sufficient to distinguish it from the bacteria (presumably) 

 causing the loss of colour in wine. Moreover, these latter as 

 already observed by Mulder attack cream of tartar first of all, 

 whilst the bacteria of mannitic fermentation leave this salt com- 

 pletely untouched. The fact, now firmly established, that a high 

 temperature (36 C. or over) favours the appearance of the last- 

 named microbes, explains the defective fermentation (familiar 

 to Sicilian and Algerian wine-growers) of wine-must during the 

 prevalence of the hot south wind (sirocco or simoom), the red 

 wines, in particular, being greatly affected. According to G. 

 BASILS (L), this wine disease is as frequent in Sicily as it is 

 dreaded, and in some years affects the greater part of the vintage. 



The bacteria here coming into action can be destroyed by 

 heating up to 60 C., a treatment impossible to apply hitherto on 

 account of its fatal effect on yeast-cells. However, by artificially 

 inoculating (pitching) with strong, pure yeast, and by cooling the 

 mash down to i5-2o C., the liquid could be rapidly brought 

 into a state of alcoholic fermentation, which could be controlled 

 by suitably regulating the temperature. In this way the desired 

 result would be ensured, and would amply repay the increased 

 outlay required. In this connection the experience gained by 

 M. RIETSCH and M. HERSELIN (I.) should also be borne in mind, 

 viz., that the injurious influence of an excessively high temperature 

 (36 C.) can be reduced by aerating the fermenting liquid. 



In conclusion, it will be useful to remember that mannite is 

 also formed during the mucinous fermentation of sugar, and that 

 this hexavalent alcohol is also excreted as a metabolic product by 

 certain Eumycetes, e.g. Penicillium glaucum. 



