pH: Acidity Levels of Wine
This term is one that is creeping into the vocabulary of many who wish thereby to assert their expertise in matters of wine. My friend Damien Cleeves Q. C., who is qualified to speak on such technicalities, has defined pH for me as the term pH stands for hydrogen power and is the measure of the acidity or alkalinity of a solution… Water, or a completely neutral solution, has a pH of 7. If the pH is below 7, it indicates acidity and if it is above 7, alkalinity.’ He goes on to cite the work of U.S. Authorities, Amerine and Creuss, relating to musts, and then says ‘The measurement of pH will indicate either volatile or fixed acidity, or both – and of course both are always present in any wine, since the volatile acids include not only acetic (which is produced to a limited extent even in a healthy fermentation) but also lactic and others . . .but I urge you not to simplify the matter by suggesting that the pH is determined solely by the amount of acids present. There is always a substantial buffering effect in wine, that is to say a mechanism caused by the presence of salts and the like which helps to keep the pH steady, so that the actual pH is brought about by the balance of a number of factors. The pH of wines varies in the course of the fermentation, for instance when the malo-lactic fermentation takes place, when lees fall, and so on. Mr Cleeves further states in his letter to me that, in an average of 47 red Bordeaux, the pH figure was 3.4.
The scientist will be able to understand and appraise such information but, as another distinguished scientist friend warns, ‘pH doesn’t say much about taste . . .Two wines of the same pH can taste quite different, with one having a recognisably bitter and sharp acidic taste which is absent from the other.’ This authority explains that pH is a scale from 1 to 14. Something which is a very strong acid has a low pH (say, 2 or 3) and a strong alkali has a high pH (10 or 12). Water is exactly neutral, at pH 7. The important thing is that, in the middle of the scale, a slight change of acidity makes a lot of difference to the pH reading, so it is very sensitive in that ‘delicate’ region. So if water is pH 7,an alkaline juice would be around 7.5 or 8: an acidic drink would rate less than pH 7. A drink of pH 6 is going to be more acidic than a drink of pH 6.5.’
So those people who equate the pH figure with the acidity they suppose they note in a wine, are not only oversimplifying the significance of this matter, they are being as silly as those who generalise to the effect that auslese wines are sweeter than spatlese wines, or who think they can exactly assess alcoholic strength merely by tasting. It is interesting to know the details of a wine, if such knowledge enhances one’s appreciation, understanding and enjoyment. Otherwise, such matters should be put aside while the drinker concentrates on tasting. Sometimes people ask whether a wine’s acidity is ‘good’ or ‘bad’? The answer to this must be ‘Do you like the wine?’ If the acidity balances the fruit in a healthy and well-made wine (however humble), then usually the acidity must be ‘right’; if the wine is sour and halfway to being vinegar, then of course the acidity is ‘wrong’, the wine won’t taste agreeable. If you really prefer sweetish wines, then you may not personally like a wine with natural high acidity: but there need not be anything amiss with the acidity of that wine.