Agriculture Reference
In-Depth Information
Filtration. The most common form of filtration is the use of rotary drum vacuum
(RDV) using diatomaceous earth. In general, filter pads do not have sufficient ca-
pacity for solids retention without clogging and so are seldom used. Recent devel-
opments include the use of cross flow filtration, a form of tangential flow mem-
brane filtration, for clarification of juice in addition to final wine filtration.
Fermentation of White Juice
Once the juice is clarified, it is fermented, often with a selected yeast culture, gener-
ally in a simple closed stainless steel tank. Most premium quality whites are gener-
ally fermented at low temperatures (10-15 °C) as high temperature may cause loss
of desirable fruit flavour. Therefore under warm conditions refrigeration needs to
be available either as in-place cooling plates or external heat-exchangers. In cool
areas or with late season fermentations, the opposite problem may occur and fer-
mentations may need to be warmed using the same types of heat exchangers and
heated water. Fermentation in oak barrels is also carried out when oak influence is
a desired part of the wine style. Fermentation can be stopped before completion in
order to make sweet wines, by chilling the wine to the point where the yeast ceases
to ferment and falls out of suspension
In many cases, after primary alcoholic fermentation has finished, the wine is
racked of the yeast lees to prevent the uptake of flavours and aromas derived from
the breakdown of the yeast cell wall. In other wines, the wine is deliberately left on
the yeast cells and the breakdown of the yeast encourage by yeast lees stirring (or
batonage).
Post Fermentation (Red and White Wine)
Following primary alcoholic fermentation in nearly all red wine and many white
wines, the process of malolactic fermentation (MLF) is either encouraged or dis-
couraged. It is also possible to perform MLF during alcoholic fermentation, a pro-
cess known as co-inoculation.
Malolactic Fermentation (MLF)
Malolactic fermentation converts malic acid (derived from grapes) to lactic acid and
is conducted by lactic acid bacteria.
• MLF improves the stability of the wine, because when all the malic acid is
consumed, the wine will not undergo a further MLF in the bottle.
• MLF reduces the acidity, which can be an advantage in countries with wines of
natural high acidity.
