Measuring the pH of a wine is one of the most important tests in a winery. Here are some facts on pH, why we need to know about it and how to measure the pH of your wine accurately.
Most of us learned about pH in chemistry class at school. If you can’t remember what it is, here is a refresher – ‘pH is a measure of a solutions acidity or alkalinity’, pH means Positive Hydrogen ion, and the pH scale is from 0 to 14. A neutral solution numerically is equal to 7, while the more alkaline the solution, the higher the number increases. An acid solution decreases from 7 as the acid level increases. Class over!
Measuring pH is of fundamental importance to any winemaker, it tells him or her so much about the wine generally. The color, oxidation, biological and chemical stability are all influenced by pH, as are the amount and strength of acids present.
Why is it necessary to measure pH?
Because it tells us how stable the wine is. Some micro organisms find it easier to grow at a higher pH, so it is important to control this growth. This is done by accurate and consistent use of sulfur dioxide (SO2) as an anti bacterial agent. The effectiveness of control reduces as the SO2 level reduces and the wine pH increases.
What is the optimum pH for a wine?
The optimum range for a good quality wine is pH3.2 to pH3.6. Lower than pH3.2 will diminish survival rates of both yeast and malolactic bacteria, while higher than pH3.6 will enable harmful bacteria to flourish and therefore cause the wine to deteriorate.
Is there a relationship between pH and total acidity?
To some extent there is a relationship between the two, however, it is not that straight forward. As pH can measure the amount of acids present, ie. the total quantity of acids, it also measures the tartaric to the malic acid ratio as well as the amount of potassium in the wine.
Wines containing lower acid and more potassium will show higher pH values, whereas wines with more tartaric acid, less malic acid and less potassium will have lower pH values.
As wine contains a mix of acids, predominantly tartaric, with some malic, citric and lactic, pH alone cannot express the acidity of the wine. And so this is why titratable acidity (TA) is also measured. TA represents the amount of tartaric acid that is present in the wine, and values range from 7-12 g/l.
How can the pH and TA levels be adjusted?
It is convenient that pH and TA can be adjusted together at the same time. To increase the acid, many winemakers add pre-purchased tartaric acid powder for red wines, and maybe a combination of two-thirds tartaric to one-third malic for whites. It is difficult to achieve an exact pH especially as wine is a buffered solution. Predicting how a certain g/l acid addition will adjust the pH is not easy. Even professional winemakers struggle with this, and ultimately it comes down to experience and vineyard knowledge.
The best way, and most accurate, is to get the musts measured for total acidity in g/l. Good wine laboratories can undertake these analyses for you. Once the TA is measured, you will know exactly how much acid to add per liter of wine to adjust the TA by the numbers. Some examples of pH ranges for:
- Californian whites – 5.5 to 8.0 g/l
- Californian reds – 5.0 to 6.5 g/l
NB. Not to forget that it is a decision always based on other factors, such as Balance, Taste, and Flavour as well.
About tartaric acid?
Tartaric acid is a naturally present acid in the grape. It is not consumed by yeasts or by any other microorganism during the winemaking process, but remains in the wine. These small acid crystals – much the same size as grains of sugar – can be removed from the wine by a process of cold stabilization. Failing to remove the crystals when the wine is cold will allow them to either redissolve and stay in the wine, only to settle out if and when the wine gets cold.
If you have ever seen these small crystals at the base of a glass of wine or bottle, don’t worry, they are completely harmless. They are referred to as ‘potassium tartrate crystals’ or ‘wine diamonds’, and are just rather unsightly.
pH TESTING EQUIPMENT
- Hanna Checker-1 Digital pH Meter. This is a small hand-held electronic pH meter which is easy to read and use. It is highly accurate with 0.01 resolution and a replaceable electrode. It does require calibrating solutions.
- HI 222 Professional pH Meter. This meter allows for automatic pH calibration at pH3 and pH7. Most conventional pH meters fail to warn the user when the pH electrode is dirty, but this meter uses Hanna’s signature Calibration Check(TM) technology to detect a dirty electrode and warn the user during calibration.
It can be seen how important it is to measure pH, so you will end up with an attractive, stable and well-balanced wine. It might sound complicated, but using your educated wine palate along with a little pH testing meter, you will never look back and leave it to chance.