The Production of Wine - Oenology

English Wine is the fermented juice of freshly picked grapes grown in England and Wales. Oenology is the science of wine and viniculture or vinification the practical art of wine production.

The wine maker combines both the art and the science to produce quality wines. The principle of wine making is that sugar in the grape is converted by wine yeast into alcohol and carbon dioxide gas.

This complex micro-biological chain reaction is called fermentation and, unimpeded, will continue until all the fermentable sugars are converted. The skill of the wine maker lies in knowing how to treat this volatile liquid.

After the Harvest - Pressing the Grapes

The harvest grapes are brought to the winery as quickly as possible. Delay would allow the fruit to oxidise and take on off-flavours.

On arrival at the press the bunches of grapes are usually, but not always, de-stemmed and then milled to break up the berries.

A careful amount of sulphur dioxide may be added (used in some vineyards) as a sterilant and the grapes then pressed.

There are several types of wine press - most still visibly derived from the traditional basket and screw spindle design.

Modern presses are increasingly mechanised and automated, one particular group being based on the use of pneumatic pressure.

A large bag lying centrally through the cylinder of the press is filled with air and so squeezes the grapes between its expanding self and the sides of the drum.

Irrespective of the capacity of the press - varying from a half to ten tons - the pressing cycle lasts about two hours at the end of which all the juice has been extracted.

The almost dry residue can be returned to the vineyard as manure. After pressing, the juice or must, as it is called, has to be clarified either by centrifugal separation or by settling for up to 24 hours.

At this stage, if sometimes necessary, the must is de-acidified. It may be chaptalised if that too is needed.

Chapterisation

Chaptalisation is the process whereby sugar is added in order to bring the eventual alcoholic content of the wine up to the desired level if, at the harvest, the sugar content in the grapes was not high enough.

The must is then inoculated with a pure culture of wine yeast and fermentation begins.

English wine is remarkable for its freshness, aroma and delicacy of flavour.

In order to capture this, the fermentation (which gives off heat) must not be allowed to run too hot and so `boil off` the flavours but must be maintained at an average temperature no higher than 15 degrees C.

This fermentation, at first very vigorous and then slowing down, will last for up to three weeks until all the sugar is converted to alcohol and carbon dioxide.

The new wine is `racked off` its sediment into a clean tank and then left to mature. Night air will chill the winery and cold-stabilise the wine, bringing out any crystalline deposits.

The new style wineries in England now have controlled temperature rooms built into their buildings to manage red and white style wines.