Winemaking - The Facts

How does a grape get from vineyard to bottle?


Winemaking - Cleaning up and bottling

At the end of the maturation period the wine needs to be cleaned up in
preparation for bottling. There are a number of techniques that can be
used to stabilise and clarify wine:

Fining - this is done by
adding a fining agent to the wine which causes the lees to fall to the
bottom from where they can be racked off. The main fining agent for
white wine is a clay called Bentonite. Red wines are traditionally fined
with beaten egg white, or other protein rich substances like gelatin.

- by spinning a wine at high speed yeast and bacteria can be removed
from a wine. Cold treatment (or 'tartrate stabilisation'). Many white
wines are held at -3 degrees for a week just before bottling. This cold
treatment precipitates out any excess tartaric acid in the form of
tartrate crystals, hopefully preventing a crystal deposit forming in the
bottle later.Filtration - this is the process used to remove any
remaining yeast or bacteria from a wine. There are three main types of
1. Kieselguhr (or 'diatomaceous earth') - to a layman it
looks as if the wine is being filtered through mud. Used as the first
stage in cleaning up a wine containing lots of yeast.
2. Cellulose
(or 'plate and frame') - these filter pads look like thick pieces of
white cardboard. Effective in removing most remaining yeast. 3. Membrane
(or 'sterile') - made of synthetic polymers, a membrane filter will
remove all remaining yeast or bacteria.

Pasteurisation - heat
treating a wine just before or during bottling is still occasionally
used to be sure that there are no active microbes present. However, the
damage caused to wine by flash pasteurisation, coupled with the
availability of membrane filters, has seen a decline in the use of
pasteurisation in wine production. Hence most wines nowadays are 'cold
sterile bottled'.

If all or most of the above techniques are
used on a wine it will almost definitely be clear and stable when
bottled. However, each of these manipulations inevitably strips some
flavour and character from a wine. There is an ongoing debate in the
wine industry as to how much a winemaker should or shouldn't do to his
wine to reconcile the need for stability on the one hand, with flavour
and character on the other.

Modern wine bottling lines are clean,
highly automated facilities. Hygiene and sterility are priorities to
try and ensure that the risks of contamination and oxidation are
minimised. Various techniques exist to ensure that the bottles
themselves are clean, and that the wine does not suffer too much air
contact during the filling itself. The big debate at the moment concerns
the use of natural cork to close the bottle. Natural cork is a tried
and tested material, but it is increasingly expensive, and can spoil a
wine through cork taint or by allowing air into the bottle. The use of
synthetic cork is on the rise, whilst others advocate the use of screw
tops or beer bottle tops for day-to-day wines.

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