Labo Vin Help: Correcting the wine

Correcting the wine

At the end of the alcoholic fermentation, the young wine must be carefully checked and analysed in order to verify if it is true to what was awaited, and eventually correct the flaws.

1) Wine control

a. The alcoholic rate

This measure, using a vinometer, allows verifying if the alcohol rate matches to the potential alcohol defined before fermentation. Otherwise, if the difference is more than 0.5 % vol, an error was committed (sugar calculation, density reading, amount of yeast nutrients, fermentation...). As far as sweet wines are concerned, a rate of 15 % vol is fulfilling, as it matches to the maximum accepted by the yeasts used for this kind of wine (yeast bearing a higher alcoholic rate will yield a dry wine with a high alcoholic rate).

b. Pectin residues

If enough pectinase [ The pectinase is an enzyme (protein, biological catalyst) that destroys the pectin. It follows a better flavours extraction, a better sap yield, along with a good ulterior clarification. The pectinase is sold as a liquid or a powder. Conform to the manufacturers instructions. Too much pectinase is not damaging, but it is wasting. ] were used at the fermentation start, no more pectin should be found in the wine. Nevertheless, it is advisable to verify it by this simple test:

In a 50 mL test tube, mix 5 mL wine and 20 mL methanol, then shake.
Observe in the light. Pectin should appear as big flakes (do not confuse with small protein flakes that can be observed in nearly all the wines). If the test is doubtful, look once more after half an hour rest.

c. Tannin

The savour of a young wine is different from a mature wine; its quality is still difficult to assess. The most important is to estimate its tannin [ The word tannin applies to various badly defined compounds, often polyphenolic acids esterified by a sugar. The tannins are very widespread in a lot of plants, mostly barks, fruits, tree leaves, oak wood...
The oenological trade tannin is mostly extracted from oak apple, sometimes also from grape skin.
The tannin has a typical astringent savour and a characteristic subtle odour. It is an amorphous pale yellow to brown powder. The tannin is essential in a wine: it is necessary for the wine clarification (min. 3 g/10 L juice). It forms insoluble compounds with proteins and metallic ions, starch and a lot of alcaloids. It also contributes much to the wine keeping. The tannin content of wines varies from 350 mg/L in white wines up to more than de 3 g/L in red wines. Ageing wines in oak casks increases their tannin content. ] rate. The tannin imparts the wine a astringent bitter savour. Let turn a gulp wine in your mouth, then eliminate it (swallow or spit it out). If your mouth remains harsh (like with a sloe), the wine contains tannin. (Do not confuse the astringency with the bitterness of a young wine, due to the presence of yeast). The wines issued from citrus fruits, peaches, plums, apricots, elder, blueberries and black currant, often contain much tannin.

2) Correcting the wine

Barring if sparkling wine is intended, add, for 10 L, 10 mL metaK [ Solution 0.25 M of potassium metabisulfite (K₂S₂O₅, Mr=222), prepared by dissolving in water 55.5 g potassium metabisulfite (failing which, 47.5 g sodium metabisulfite - Na₂S₂O₅, Mr=190) for 1 L solution.
10 mL of this solution equals 320 mg SO₂ (5 millimoles).
This solution can be kept for a long time in a tightly sealed bottle. ] .
If the astringency is questionable, dissolve 3 g/10 L tannin in a bit alcohol, dilute it with a little wine and pour it into the wine.
Shut the container, stir vigorously and keep the wine at temperature of about 20° C during 24 h. Then store the wine in a place as cold as possible (below 10° C and better near 0° C, and even down to -2° C [the wine freezes at around -5° C]).

3) Clarification and refining

To clarify a wine is to make it perfectly clear and bright. This processing reduces the risk of wine alteration. Three factors favour the clarification:

Cold: wine storage in a very cold place (above -5° C) mightily helps clarifying.
Using clarifying agents.
Filtration. It is rarely necessary, though systematically used in great wineries. By preliminarily using pectinase and tannin, the clarification often occurs spontaneously and cold is enough.

Refining [ Refining a wine is reducing its tannin content to a right level. ] is carried out along with clarification. After maximum 1-2 weeks keeping in the cold, the wine must be racked.

Preliminarily, carry out the clarification-refining test [ - One or two days before racking, fill with wine 5 100 mL bottles numbered 0, 1, 2, 3 and 4.
- Whip up an egg white with a little water and bring it to 1 litre, integrating the foam.
- Add to the bottles from this solution as many times 1 mL than the number the bottle bears. Close, shake the bottles and place them in a fridge without shaking any more. The racking day, pick out the clearer bottle that is suitably astringent and note its number (the bottle 0 must be the less clear).
If several bottles are clear, choose the bottle being rightly astringent; the egg white has indeed reduced the tannin content.
- Rack the wine, adding to it, for 1 litre, an egg white solution volume matching up to 10 times the chosen bottle number. ] . This is very important and must be carried out carefully and the amount of egg white precisely defined. The wine will not clarify if too little egg white is used. In return, if too much egg white is added, all the tannin is removed and a new cloud appears. The wine is told "overrefined" (the remedy is tannin addition). If the wine is not really too tannic, it is better to choose the clearer flask containing a minimum egg white.

Other clarification agents than egg white can be used (gelatine, bentonite, ichtyocolle...). No one is miraculous and we will not speak about them.