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Whenever possible the vatting of the grape pulp should be 
done by gravitation; time and labour is saved, and the work is done 
with greater cleanliness. 
The filling of the vat should be done during the day, and not 
spread over two or three days. 
It is immaterial whether only one or several kinds of grapes 
are mixed together in the vat, provided that they be all of one type 
and are meant for making one class of wine. Each sort is, however, 
generally fermented apart from the other, and the resulting wine is 
blended afterwards if required. 
The vats should not be filled to more than four-fifths of their 
capacity, as much swelling of the mass occurs during fermentation, 
and if the rise of the liquid occurred during night time loss of wine 
would result. By keeping the level of the fermenting must below 
the edge of the vat, excess of air is to a great extent screened off 
by a layer of carbonic acid gas; which being about three times as 
heavy as air, covers the fermenting liquid and prevents oxidation 
and acetification of the cap or floating husks. 
Questions are often asked: Should the fermentation be con- 
ducted in open or in closed vessels? Should the skins or caps be 
kept immersed or left to float during fermentation? In both cases, 
more especially im hot countries, both theory and practice strongly 
favour open vats and submerged heads. There takes place during 
fermentation a chemical reaction which results in the splitting up 
of grape sugar into alcohol and carbonic acid. This reaction, which 
is set up by living organisms or yeast, is accompanied by much 
evolutions of heat, and the richer the liquid is in sugar, the hotter 
the temperature, within limits, which we will consider presently, 
the greater that evolution of heat becomes. 
Unless some means offer of dissipating that heat generated 
during fermentation, its accumulation might reach a point which 
would soon endanger the life of the acive agent of fermentation. 
Fortunately, two natural outlets exist for the dissemination of that 
generated heat: Ist, radiation from the surface and through the 
sides of the fermenting vessels; 2nd, the free escape of the car- 
bonie acid gas. which rises to the surface in warm bubbles which 
burst and allow it to escape. 
Closed vats, such as are used in the Medoe and other districts 
where the must is lighter, the temperature cooler, and the wine- 
makers most conservative in their methods, would in hotter 
climates, where the grapes are richer in sugar, prove an element of 
danger, for the reason that the confined heated carbonie acid gas, 
prevented from escaping freely from the fermenting mass, tends to 
raise its temperature beyond the limits desirable. 
