Making Wine : Vinification
Source: morethanorganic
Vinification is the process of turning grapes into Wine. Grapes naturally possess everything that is needed to make wine and in natural wine, ripe organic grapes are the only ingredient.
In conventional winemaking large numbers of additives are used to speed up and control this process, and to ensure a safe, predictable product.
Overview
Central to the process is fermentation, the conversion of the grape's natural sugars into alcohol and carbon dioxide.
Vinification can be roughly divided into what happens before, during, and after fermentation. Below is a brief sketch of the most important points.
Before fermentation
- Harvesting
Best done by hand, commonly done by machine.
- Crushing/pressing
The skin of the grapes is broken to release the sugary juices, exposing them to the yeasts for fermentation.
Fermentation
There are generally two types of fermentation in wine, which may or may not take place simultaneously.
- Primary fermentation
The conversion of the grape's stored sugars into alchohol and carbon dioxide. Carried out by yeasts.
- Malolactic fermentation
The conversion of malic acid into lactic acid and carbon dioxide. This changes the taste of the wine but does not affect its alcohol content.
After fermentation
- Maturing
Wines may be left to mature in barrels for as much as three years before being bottled for release.
- Clarification
Conventional wines will be cleaned up in a variety of ways, and sterile filtered before bottling.
- Bottling
It is almost universal practice to add sulphur dioxide at this point, to prevent or retard changes in the bottle.
Some winemakers will further mature their wines in bottle before they are sold.
Fermentation
Even a very complex wine is only alcoholic grape juice. The alcohol is produced by a process called fermentation.
Fermentation requires two things : sugars and yeasts.
A ripe organic grape is full of natural sugars and there are wild yeasts living on its skin. As soon as the skin of the grape is broken, fermentation can begin.
To make wine, all the winemaker has to do is collect his grapes and gently crush them, releasing the sugary juice and exposing it to the yeasts.
Fermentation will continue until all the sugar has been turned into alcohol or the level of alcohol in the juice reaches around fifteen percent, whichever is sooner.
At around fifteen percent alcohol, the yeasts will die naturally and any left over sugars will remain in the wine.
Yeasts
A natural wine is fermented only with the wild yeasts native to its terroir.
Yeast strains vary widely from place to place and contribute significantly to the odour of the finished wine. The yeasts indigenous to a particular area are an important part of what gives its wines their character.
Conventionally grown grapes have little or no wild yeast living on their skin.
The winemaker will kill whatever yeast remains with sulphur dioxide, and reseed the grapes with a single strain of commercially produced yeast.
Wines fermented in this way have less personality, all using the same few commercial yeast strains, and are less an expression of their terroir. This is one reason they taste so similar.
They are also less complex, as each of the many wild yeasts present on an organic grape will contribute something to the finished wine.
Sugars
The level of alcohol in the finished wine is determined by the level of sugar in the grapes from which it is made.
More sugar means there is more for the yeast to convert into alcohol.
Grapes grown further north see less sun and therefore contain less stored sugar than those grown in the south. Traditionally, therefore, northern wines contain a lower level of alcohol.
Chaptalization is a way of boosting the level of alcohol in the finished wine by adding sugar to the juice during fermentation.The technique is named after Jean Antoine Chaptal, Napoleon's minister for agriculture, who is said to have invented it.
A natural wine is fermented only with its own sugars.
Malolactic fermentation
Malolactic fermentation is a secondary process of bacterial conversion, which may follow or overlap with primary fermentation.
Harsher tasting malic acid is converted into softer, and less acidic, lactic acid. Carbon dioxide is also produced.
In practical terms this means a reduction in the acidity of the wine and an increase in its complexity. The level of alcohol is unaffected.
Like primary fermentation, malolactic fermentation can be induced by the introduction of cultured bacteria, or suppressed with sulphur dioxide.
If a wine is bottled quickly, it may take place inside the bottle. One reason SO2 is used at bottling is to prevent this.
A natural winemaker has to wait for the malo to finish naturally before he can bottle his wine.
Factors Impacting the Fermentation
Source: Viticulture & Enology
Several factors impact the initiation and progression of the malolactic fermentation. Temperature, pH, acidity, ethanol, sulfite and availability of nutrients are all important for the growth and metabolic activities of the Lactic Acid Bacteria. The lactic acid bacteria are more fastidious in their growth requirements than the yeast. It can be challenging to get the malolactic conversion to occur at the desired time in the wine.
The lactic acid bacteria generally require higher temperatures than the yeast in order to grow. The temperature should be above 18°C (64°F) to allow growth of the bacteria. The bacteria will grow more rapidly at higher temperatures but this can lead to deterioration of the wine. Successful malolactic conversions have been reported to occur at lower temperatures and this may indicate some strains can develop temperature tolerance but this is not a general phenomenon.
