What is “pH”? What does it mean and what does it say about a wine? How do you use a pH meter?
A new winemaker eventually grasps the meaning and the importance to pay attention to specific gravity and total titratable acidity. This often occurs after a trail of horrid wines which marks the learning process.
The more a new winemaker starts to study wine, the more the “pH” thing seems to creep up. Then they are told that to truly make better one, one needs to invest in a pH meter and start doing accurate measurements of pH levels, etc…
It can be daunting to a new winemaker as it is expressed in complexities that can instill fear and boggle their minds. Small wonder that some of the more conservative amongst us don’t even want to hear or deal with pH… 😉
Well, the only thing wrong with pH is that we have been trying to understand it.
Like a lot of other things in life, pH is what you make of it. It is easy to learn to use pH, and you don’t really need to understand it. Most of us don’t understand the cars we drive so easily, or the TV sets we so blithely manipulate.
Start by simply recognizing pH as a very important number that can help you to make better wines. True, it doesn’t work like most numbers we grew up with, because what it measures grows greater as the pH number gets smaller. Those of us who have lived long enough to watch what has happened to the value of the dollar bill over the past fifty years can grasp that. As we receive more and more dollar bills they become worth less and less. Not to worry.
It does help to have some understanding of what pH measures. It has to do with acids. Musts and wines are complex solutions of weak Acids mixed with a variety of other materials. It is essential that we start a wine with its acids just so.
“Total titratable acidity”, which is what you measure with a simple titration kit, is not a measure of total acid, but of the acid that is available to react with the NaOH [Sodium Hydroxide] solution with which we titrate.
It measures that available acid in grams per litre or in percentage. It does not tell us how strong that acid is, and acids vary greatly in strength.
pH is a measure of the acid strength in the must or wine. The “p” in pH is an abbreviation for the Swedish word for power.
It is pH, rather than total titratable acidity, which indicates the ability of a must to resist oxidation and invasion by bacteria, and which determines how much SO² is needed.
pH has its primary importance in checking fruit or grapes for purchase and in preparing musts.
All wine musts that are to produce satisfactory wines have to start with their pH in the range of pH 3.1 to pH 3.55 at the commencement of fermentation. What their pH becomes later is considerably less important.
More particularly, white wine grapes or light coloured fruit wines such as apple wines or ciders should have a pH close to 3.2 (3.1 to 3.3). Red wine grapes or darker fruits such as blackberries should have a pH of 3.3 to 3.4 with pH 3.55 as tops.
Anything started outside the range of pH 3.1 to 3.55 is headed for trouble or will need adjustments before we start to ferment. Below pH 3.1 the wine will be highly acidic. Above pH 3.55 the must will be gravely at risk of oxidation and of invasion by bacteria, and it will be difficult or impossible to control with metabisulphite. There are, at the least, likely to be fermentation by-products that will detract from the wine.
In high quality grapes, picked at the right point of maturity, the pH, total titratable acidity, and specific gravity will all be in their correct ranges, and no adjustment is required. Fermentation should produce a quality wine that fully shows the potential of the grape variety.
This will almost never happen with fruit wines and the fruit must will always need to be adjusted to start off at the required range of acid and pH.
In fruit which are under ripe, overripe, or too heavily cropped, and in most fruit wine musts, the pH, total titratable acid and specific gravity will deviate from their ideal ranges. They may be adjusted to those ideal ranges. They may then produce pleasant and balanced wines.
You may usually expect to be able to raise or lower the pH of a must, but in many musts, and in varying degree, the pH is reluctant to change. It seems to have a mind of its own so again, the best advise I can give in regards to pH, is not to think about it too much, know about it, learn how to adjust it the best you can but don’t stress over it too much…
Let me know if you have questions or comments about pH or your own explanation of it.