November 26, 1914] 



NATURE 



in 



cloudy and to throw out a light deposit. This 

 tendency is accompanied as a rule by more or less 

 darkening of colour, and by modifications in the 

 flavour and odour which are very characteristic. 

 Even before any casse or " break " (cloudiness) 

 is observable in them, wines undergoing- this 

 change acquire an "earthy " odour or terroir; and 

 simultaneously a distinctive bitter flavour of a 

 greater or less intensity is developed. These 

 faults- — cloudiness, earthy odour, bitterness, and 

 modification of colour — may exist in different de- 

 grees, but are apparently all related to a common 

 cause; and Dr. Brown's experiments indicate that 

 this cause is not to be sought in the action of 

 micro-organisms. The malady is conditioned by 

 purely chemical changes. Moreover, it only 

 occurs when the wine is in contact with air, or 

 with free oxygen derived from some such sourc 

 as hydrogen peroxide. 



Naturally one of the first things to ascertain in 

 studying the malady was the true character of the 

 suspended matter forming the turbidity. Under 

 the microscope it was found to consist of amor- 

 phous aggregates of minute, roughly-spherical 

 particles, which were readily stained by Coupler's 

 blue, dissolved easily by caustic alkali, and also, 

 though with some difficulty, by dilute acid. Ex- 

 cept in this last point the deposit resembles the 

 amorphous matter which separates from beer in 

 certain circumstances, and which has been shown 

 by Dr. Brown himself to consist mainly of a com- 

 bination of tannic acid with albuniiuoids. The 

 actual amount of the deposit necessary to give 

 a distinct turbidity to wine is relatively very 

 small : in one instance the weight of the substance 

 when dried was only 6*4 milligrammes per litre of 

 wine. The organic portion of the deposit con- 

 tained nitrogen equivalent to 55'9 per cent, of 

 albuminoids. When incinerated, the dry sub- 

 stance of the deposit yielded i2"g per cent, of 

 inorganic material, four-fifths of which was ferric 

 oxide. In fact, a striking feature about all the 

 deposits in this kind of casse is the comparatively 

 large proportion of iron which they contain. 



It was found, further, that an essential factor 

 in the production of casse was the presence of a 

 little iron in the ferrous state. This apparently 

 acts as a carrier of atmospheric oxygen to certain 

 oxidisable substances in the wine, much in the 

 same way as traces of ferrous salts behave in the 

 well-known " Fenton " reaction. 



Systematic experiments showed not only that 

 air and ferrous salts are necessary, but that certain 

 oxidisable substances in the wine are also re- 

 quired. Of these the most notable is tannic acid ; 

 and the author concludes that the material form- 

 ing the turbidity or deposit is in fact "a colloidal 

 combination of iron with products derived from 

 the limited oxidation of tannins and certain wine- 

 albuminoids." This does not, of course, tell us 

 all that it is desirable to know about the deposit 

 and the conditions of its formation. The question 

 of the nature and amount of the nitrogenous sub- 

 stances in the wine, and the part thev play in the 

 production of the changes, has still to be in- 



NO. 2352, VOL. 94] 



vestigated. As the author remarks, wine-making 

 has its own particular "nitrogen question," and 

 it is at present virgin ground. 



Good evidence was obtained to show that the 

 oxidising agent concerned is not a vegetable oxi- 

 dase. Freshly expressed grape juice contains no 

 oxidase, though it may dissolve some from the 

 grape skins if left in contact with them. In any 

 case there appears to be no connection between 

 the occurrence of oxidase and the casse ferrique. 

 The immediate cause of this deterioration is the 

 alternate reduction and oxidation of iron, with 

 consequent transference of oxygen to the change- 

 able tannins and other constituents of the wine. 



Now if this is true, it points the way to pre- 

 ventive and remedial measures. One such 

 measure, obviously, is to avoid so far as possible 

 the must or wine taking up iron at any stage of 

 the making or storing. If, however, an excess of 

 iron cannot be helped, it would be expected that 

 the addition of a reducing agent to maintain the 

 iron permanently in the ferrous condition would 

 prevent the occurrence of the malady. This was 

 found to be so, the action of sulphites in this 

 respect being very pronounced. Again, since 

 tannic acid is one of the essentials, its removal 

 should be beneficial ; and in fact the addition of 

 casein to the wine has a favourable influence 

 which is attributed to an adsorptive separation of 

 tannin by the casein. As regards the other essen- 

 tial condition — the presence of air — the author 

 recommends that aeration of the wine should be 

 guarded against during the maturing and bottling 

 operations, and that the bottles should be com- 

 pletely filled. In this connection it is noted as 

 unfortunate that the visitor to the Cape generally 

 makes the acquaintance of South African wines for 

 the first time on the ship going out. The bottles 

 are frequently not completely filled, and this, 

 with the alternations of temperature and the 

 swing of the ship, helps to produce Ihe malady in 

 question, especially in the more delicate white 

 wines. 



The faults mentioned are so common in the 

 white wines of South Atrica that the author at one 

 time regarded them as due to some fundamental 

 causes, such as soil and climate, which were be- 

 yond control. But the occurrence of perfectly 

 "clean" wines, the production of such wines under 

 his own auspices, and the results of the investiga- 

 tion which has been outlined, have altered this 

 view. Not Providence, but the producer, is re- 

 sponsible — or at least, the producer and the mer- 

 chant must share the responsibility. 



The scientific study of this question made by 

 Dr. Brown, necessarily incomplete though it is, 

 has given definite knowledge where hitherto in- 

 formation has been vague or absent, whilst the 

 practical application of this knowledge indicates 

 the direction in which remedial measures are to 

 I:>e sought. It is to be hoped that the author will 

 be able to extend the research to the " nitrogen 

 question " already mentioned, and with equally 

 definite results. 



C. SlMMONDS. 



