that the pH be in acceptable ranges.
You need to check pH at crush and adjust as needed. You then need to check and adjust pH after M/L, allowing your wines to age gracefully and to show their best potential.
Current wisdom suggests that your pH be below 3.6 for reds and below 3.3 for whites.
Lower pH = tighter, less accessible wines, biologically sounder, that age more slowly but gracefully.
Higher pH = more accessible wines that age more quickly, browning easily, more susceptible to spoilage.
Correcting high pH: Add Tartaric Acid. Do not panic about making the Total Acidity too high. Get the pH where you want it, at crush.Excess tartaric acid can be chilled out. Actually, wines want to come back to a natural balance, and will precipitate most of the excess acid at cellar temperature, as tartrate crystals.
This works best when tartaric acid is added at the beginning of the fermentation/aging cycle. That is, at crush and at the end of M/L.
Dose: 3.8 grams Tartaric Acid / gallon = lowers pH .1
(This also raises the Total Acidity .1 gram/liter (ppt))
Be conservative in the final correction! When the excess tartaric acid precipitates out, the acidity lowers. However, the pH also lowers. Yes, lowers!
pH lowers, though not quite as much as the acidity. This will depend on the buffering effect of the potassium in the acid pool.
Also, keep wines at pH 3.3 or above, but not above 3.6, until M/L is complete.
For example: Suppose that you want your wine to end up at pH 3.5.
You corrected the grapes at crush to pH 3.5. However (at the Post-Crush Clinic), due to skin contact, you find out that it is at pH 3.8 and your total acidity is .6g/L.. Now add tartaric acid to lower the pH to 3.6. Your total acidity will jump to .8g/L.. The wine will taste too acidic. Don't panic.
During a forced chilling or usually over a cold winter, the acidity will drop to about .6-.7 g/L.. The ph will also drop to about 3.5.. This is now a biologically stable wine that also tastes balanced.
Correcting low pH / high total acidity: Usually, excess acidity can be chilled out since tartaric acid is unstable at low temperature.How long to chill? What temperature? The cooler, the shorter time required. Two cold months might equal two weeks refrigeration.
Try freezing a sample, thawing and testing/tasting to check your potential change.
When refrigerating your wine (as low as 28*F before freezing), add crème of tartar crystal. Do this after chilling out as much tartrate as possible. This adds additional seed crystal to attract more tartaric acid.
Agitation also helps to disperse the seed crystals.
CAUTION: Cold liquids easily accept oxygen, causing browning.After chilling, let the wine warm to room temp and then rack off of the tartrate crystals.
If the acidity is still too high for the style/taste, add Potassium Carbonate.
Dose: 3.8 g/gallon (about 1/2 tsp.) may reduce the acidity by .1 g/L.
The carbonate neutralizes acidity. Like Tums to the tummy.
Additionally, if you can also chill the wine, more tartrates will drop out due to your adding more potassium to the acid pool.