Clearing
This stage in the winemaking process involves clarifying the grape juice before alcoholic fermentation. Systematic for whites and rosés, settling removes unwanted solid particles, resulting in a clear must with refined organoleptic properties.
Why remove must sludge from grapes?
Bourbes, soil and vine residues (stalks, skins and seeds), represent between 1 and 5% of the volume of the grape juice, which is then a cloudy liquid. A distinction is made between coarse, thick bourbes and finer ones. Theireffects on the must, and therefore on the taste and quality of the wine, vary from one bourbe to another.
| Sludge without oenological interest | Sludge with oenological interest |
|---|---|
| Phytosanitary residues, Heavy metals, Sulfur compounds responsible for a reduced or herbaceous taste in wine | Anthocyanins, conditioning the color of the grape variety and therefore the wine, Tannins, Native yeasts, Nutrients necessary for alcoholic fermentation (polysaccharides, etc.), Precursors of varietal aromas in wines |
| Sludge without oenological interest | Phytosanitary residues, Heavy metals, Sulfur compounds responsible for a reduced or herbaceous taste in wine |
| Sludge with oenological interest | Anthocyanins, conditioning the color of the grape variety and therefore the wine, Tannins, Native yeasts, Nutrients necessary for alcoholic fermentation (polysaccharides, etc.), Precursors of varietal aromas in wines |
The subtlety of settling lies in eliminating undesirable lees, without over-clarifying the must, which will then have difficulty fermenting properly. The efficiency of this pre-fermentation operation is assessed by measuring the turbidity and particle size of the wine.
Is settling for white or red wine?
Settling is a systematic vinification stage for white and rosé press wines. Carried out directly after pressing, it prevents maceration of the must with coloring and tannic residues. Once removed, the lees are sometimes filtered to isolate certain aromatic precursors. Reincorporated into the vat, this filtrate adds fat and enriches white wine aromas and rosés.
For red wines, maceration of the must with tannins and anthocyanins is essential. Must purification is therefore generally carried out after alcoholic fermentation, by draining the vats and pressing the pomace. Some winegrowers nevertheless decide to use racking for their red wines, then reincorporating the sludge filtrate to ensure its color and tannin structure. Although it gives the resulting wine a clearer fruitiness, this process remains rare, as it is complex and costly.
What are the different stages in the settling process and the techniques used?
Sludge sedimentation to separate the solid phase from the liquid phase of the must
We talk about natural sedimentation when it occurs solely through the action of enzymes naturally present in the bourbe, brought to a temperature of 5 to 10°C. These enzymes flocculate the must, which falls to the bottom of the tank within 12 to 48 hours.
We talk about enzymatic sedimentation when accelerated - and yield optimized - by the addition of pectolytic enzymes.
Both types of sedimentation correspond to a static settling.
We talk about mechanical sedimentation when carried out by :
- filtration using a rotary vacuum filter,
- centrifugation in a centrifuge,
- flotation using gases and flotation devices.
This type of sedimentation corresponds to faster dynamic settling.
Racking the clear juice
When the must reaches the desired turbidity due to sedimentation of the sludge, it's time to finish settling by pumping the clear juice to the fermentation tanks.