It is second in importance only to the must sugar levels. Fluctuations in pH could mean the difference between a wine going down the sink and one you hang a double gold medal on.
What is pH exactly?
The pH scale technically is a logarithmic scale that measures the concentration of free hydrogen ions floating around in your wine. The stronger the acid the more hydrogen ions you’ll have so in essence it is a measurement of how strong an acid is.
The scale used to measure pH originally went from 0 to 14 with neutral fluids being at 7.0. Today, however, there are acids and bases that go beyond this scale.
Acids have a pH less than 7.0 while bases have a pH higher than 7.0. Plain water measures 7.0. Most wines fall between 3.0 and 3.6.
Young, unripe grapes have high acid levels. As the fruit ripens the acid levels decrease. An over ripe grape will have very low levels of acid.
The trick for wine makers during harvest is choosing when to harvest the grape. They must harvest when the pH is at a satisfactory level but also as the grapes ripen the sugar, titratable acidity, and tannins are all also changing. So when to pick the grapes is based on when all these elements come into alignment to yield the best possible wine.
In Technology of Winemaking the following pH ranges are recommended for wine musts:
- White Wines < 3.3
- Red Wines < 3.4
- Sweet Wines < 3.4
- Dessert Wines < 3.6
This makes sense as white wines are generally better with higher acid (lower pH) and sweet dessert wines would necessarily have a lower acid (higher pH) due to the ripeness of the fruit at the time of pressing.
How Does pH Affect My Wine?
In essence it affects nearly every aspect of your wine. The pH affect flavor, aroma, color, tartrate precipitation, carbon dioxide absorption, malolactic fermentation, stability, ageablity, and fermentation rate. These are just a handful of the more noticeable affects. It can also affect the many chemical reactions that take place in a wine during and after fermentation.
With the right acid level, which is subjective to a point, you can lock in flavors, aroma, a healthy color, and make sure your wine has good mouthfeel. Your fermentation will also go more smoothly.
When the acid levels are too low your wine will lack body, the mouthfeel will be off, and it will taste weak or flabby. The wine can also pick up a brownish hue.
Equally important is its effect on stability. Most types of bacteria and a few types of fungi are quite unhappy at pH levels of 3.0 to 3.75. For a finished with this is great because it is a natural protection agains spoilage micro organisms.
There are times though when being in this idea pH range can be a problem. For instance, if you were planning on doing malolactic fermentation and your wine is closer to 3.0 the malolactic bacteria may not be able to survive long enough to do their job.
The best practice is to make your pH adjustments to the wine must before fermentation begins. Actually we want to get everything in line before we unleash the yeast to do their work. This means adjusting not only the pH but also sugar content, titratable acidity, and tannins.
There are a handful of ways to adjust the pH, here are the most widely used methods:
- malolactic fermentation (deacidifies wine)
- blending similar finished wines with different acid levels (can be used to raise or lower pH)
- using chemical means (least recommended method)
Increasing acid levels in a wine chemically is pretty straight forward. It involves the addition of an acid blend containing malic, citric, and tartaric acids. Deacidifying wines chemically is done with calcium carbonate and should only be done to make very minor adjustments. It is preferable to use malolactic fermentation or cold stabilization to precipitate tartaric acid out of solution to decrease acidity.
Diagram of pH scale By PH_scale_2.png:Piercetheorganist at en.wikipedia derivative work: Agne27 (PH_scale_2.png) [Public domain], from Wikimedia Commons
Photo of wine testing lab By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons