MICROBIOLOGY OF ALCOHOL AND ALCOHOLIC PRODUCTS. 433 



ture tends to renew the activity of the microorganisms which always remain in the 

 wine. A well made wine at this time should be perfectly bright and all solid matters 

 consisting of yeast and bacteria, coagulated proteins and crystals of bitartrate 

 should have accumulated in the sediment. 



Racking should take place when possible only in settled weather, when the baro- 

 metric pressure is high. Low atmospheric pressures diminish the solubility of the 

 carbon dioxide with which the wine is saturated. Under these conditions, therefore, 

 bubbles of gas are apt to be given off, bringing up particles of sediment and rendering 

 the wine cloudy. However long wine is kept in wooden casks, it will continue to 

 deposit sediment owing to chemical changes due to the action of oxygen which pene- 

 trates slowly through the wood. Repeated rackings are therefore necessary, oc- 

 curring at least twice a year until the wine is bottled or consumed. 



Abundant aeration is necessary during fermentation. A moderate supply of 

 oxygen is necessary for the proper aging of wine. Experience has shown that exactly 

 the proper amount of pure filtered air will obtain access to the wine for the latter pur- 

 pose through the wood of ordinary casks of proper size. If the casks are too small the 

 oxidation may be too rapid, if too large the maturing of the wine may be unduly pro- 

 longed. The temperature of the storage cellar is the main modifying factor. The 

 warmer the cellar the larger the casks should be. 



With sound, completely fermented wines, all aeration, other than that due to the 

 porosity of the wood, should be avoided as much as possible. This is accomplished by 

 keeping the casks tightly bunged and completely filled. Evaporation through the wood 

 continually diminishes the volume of wine and the lack must be supplied by Jilting up, at 

 first two or three times a month and later every month or two. The drier the air of the 

 cellar, the more frequent the fillings necessary. 



A light sulphuring of the clean casks into which the wine is racked is usual. 

 This should be practised with great caution. Very little is needed with sound wines, 

 especially if it has been used before or during fermentation and a slight excess will 

 injure the flavor. The amount should not exceed 1.25 g. per hectoliter for red or 

 2 g. for white wine. One-half to one-third of this is sufficient for old wines. 

 The amount can be accurately measured only when using metabisulphite or the 

 liquefied gas. The utility of the sulphur dioxide with perfectly sound wines is to dimin- 

 ish oxidation; with wines liable to disease to discourage the growth of bacteria. 



All the manipulation of the wine should be conducted with strict attention to 

 cleanliness. This applies especially to empty casks, pumps and hoses. These should 

 be thoroughly cleaned immediately after use and, if of metal or other non-absorbent 

 material, kept perfectly dry. Utensils of wood, rubber or other porous material should 

 be preserved from bacterial or mold growth with sulphurous acid. 



The clarification of a perfectly sound wine may be facilitated and hastened by 

 thoroughly stirring up the yeast immediately before racking. The yeast in settling 

 carries down much of the finer suspended matter, thus effecting a rough fining. Mate- 

 rials such as kaolin, pure silica sand, charcoal and filter-paper can be used with the 

 same effect. The fining, however, is never perfect and the flavor of the wine is often 

 injured. A very pure clay, known commercially as Spanish clay, is used largely for 

 clearing sweet wines where the flavor is not so delicate. From 75 to 125 mg. per 

 hectoliter are used for this purpose. 

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