Agriculture Reference
In-Depth Information
Crushing and Destemming
Destemmers consist of spirally-arranged, radial fingers which rotate in a holed cyl-
inder and remove the rachis with remarkable effectiveness. Typically the stems to
be discarded are collected in a bin or removed from the receival area using a con-
veyor system. The crusher is often incorporated directly under the destemmer and
should break the berry skins with little pulping or other damage using a wringer or
mangle action. After crushing, the must (a term used to describe crushed grapes), is
pumped to the press (for white grapes) or directly to the fermentation vessel for red
wine fermentation. Some red wines are produced using a whole bunch component
(ie no destemming and crushing) to impart a stem and carbonic maceration charac-
ter (see below) in the wine.
Red Wine Fermentation
Some wine styles/varieties benefit from a “cold soak”, where the must is usually
chilled to a temperature whereby fermentation is inhibited. An addition of sulfur
dioxide (SO
2
) also helps limit microbial spoilage and oxidation. The majority of
red wines produced in the new-world are inoculated with commercially prepared
yeast, however indigenous yeast are often utilised to help provide a diversity of both
flavours and textures. Other possible additions at the beginning or during fermenta-
tion include nutrient supplements, the most important being nitrogen and vitamins.
These are added depending on the nutritional status of the juice and help prevent
stuck/sluggish fermentation and prevent off aromas such as hydrogen sulphide pro-
duction by yeast.
During red fermentation the skins form a dense 'cap' at the top of the vessel and
most fermenter designs incorporate features to facilitate colour extraction from the
cap and to separate the juice/wine and cap when sufficient colour has been extracted
in the later stages of the fermentation. Specifically, the requirements for a red fer-
menter are as follows:
• for maximal colour extraction the cap should be kept submerged or percolated
by the fermenting juice. Depending on fermenter type (open, closed, roto or red),
heading down boards, manual or automatic plunging or punch downs, automatic
or manual pump-overs or a technique referred to as rack and return can be em-
ployed.
• the fermentation temperature needs to be controlled, and in Australia this gener-
ally involves refrigeration to maintain the ferment at approximately 28-30 °C
• the juice should be easily run off at the end of the 'on skins' part of the fermenta-
tion;
• the wet marc (seeds and skins) should be easily removed for pressing.
