522 MICROBIOLOGY OP SPECIAL INDUSTRIES 



matters consisting of yeast and bacteria, coagulated proteins and crystals of bi- 

 tartrate 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 doxide 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 fiUed. Evaporation through the 

 wood continually diminishes the volume of wine and the lack must be supplied by 

 filling 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 diminish 

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



All 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 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 new wine may be facilitated and hastened 

 by thoroughly stirring up the yeast one or two days before racking. The yeast in 

 settling carries down much of the finer suspended matter, thus effecting a rough 

 fining. Materials 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 7S to 125 mg. per hectoliter are used for this purpose. 



The best wines are nearly always fined at least once, immediately before bottling. 

 One or two finings may precede this to hasten aging, defecation and bottle ripeness. 



