4.1.5.b Managing extraction

What physical parameters should be taken into account?

Alcohol content

Ethanol is the most important parameter during the winemaking process. Its concentration has a significant effect on extraction kinetics. Three categories of phenolic compounds can be distinguished in terms of extractability.
Anthocyanins are water soluble, skin tannins are also water soluble but to a lesser extent; they need a small amount of alcohol to facilitate extraction.
Finally, the seed tannins need ethanol to be extracted. In practice, the anthocyanins are extracted as soon as the wine is put in the vat, followed by the skin tannins and lastly the seed tannins.

By correctly estimating the alcohol content, it becomes possible to choose the phenolic portion to be targeted through different extraction practices carried out at the appropriate moment. The amount of alcohol is estimated by monitoring the must's density.
As a guideline, the seed tannins begin to be extracted significantly around 1030, taking 1095 as the initial density. From this data, it is possible to adjust the extraction procedures to prioritize one category of compounds over another. For example, pre-fermentation cold maceration can be used to extract more anthocyanins, or a partial pumping-over at the beginning and middle of the fermentation to extract more skin tannins.

Temperature

Like alcohol, temperature is a crucial parameter to monitor. Excessive temperatures (above 30°C) can have several consequences, including stuck fermentation or accelerated fermentation that does not leave enough time for proper extraction. Controlling the temperature during fermentation also enables adjustment of the extraction time and of the extractable portion of the berries' phenolic compounds.

Temperature control system at Château Latour

Overall, the higher the temperature, the easier extraction becomes. Different techniques coupled with temperature control allow a type of extraction to be targeted. Remember that the temperature/alcohol combination is often the best lever for successful extraction.

For example, if the skins are thick, it is preferable to carry out extraction operations (pumping over, punching down, racking) at relatively high temperatures and in the presence of alcohol, i.e. once the fermentation is well advanced (between 1070 and 1040).
The vinification temperature also has a significant impact on the wine's aromatic profile. This impact can be very pronounced and has been studied in white wines See detailed explanation of white wine vinification

Densité	Anthocyanes	Tanins de pellicules	Tanins de pépins
1100	++	+/-	/
1090	++	+	/
1080	+++	++	/
1070	+++	+++	/
1060	+++	+++	/
1050	+++	+++	+/-
1040	+++	+++	+/-
1030	+++	+++	+
1020	+++	+++	++
1010	+++	+++	++
1000	+++	+++	+++

What elements enable extraction to be monitored and controlled

Knowledge of the raw materials is a very important element that can be acquired through experience and analysis. It is essential to know:

The grape varietal characteristics (amount of polyphenols, extractability)
The plot's qualitative potential: over-extraction of raw materials of insufficient quality can lead to unbalanced wines
Its health status
Its level of ripeness via maturity tests and/or analysis of the incoming grape harvest: vigilance is required with regard to material that is too ripe or insufficiently ripe

The IPT (total polyphenols index) and anthocyanin content:_ give an idea of the quantity of polyphenols in the wine. Thus we can see the impact of extraction procedures on the vat. This analysis can be done daily or at around 1000 density.
Tasting: at this stage, it is very difficult to assess by tasting, but evaluation of colour is possible, as well as any olfactory defects (reduction, acetates, etc.) and at the end of the fermentation, we can begin to appreciate the wine's structure.

Contribute Print

Contribute