Monitoring and Adjusting pH (WineMaker)

I am always surprised at how many winemakers—new and experienced alike—still make wine with absolutely no concern for pH. It’s akin to never checking your engine oil in your car. Sooner or later, you’ll be left stranded by the side of the road, hood open, and smoke billowing from the engine…or with a case of spoiled wine.

pH greatly affects the taste of wine as well as microbial stability.

It can make the difference between drinking the wine or pouring it down the drain. Sure, you may have been making wine for years and never had problems so now you are wondering what the big deal is. Ok, consider yourself lucky. But what if I told you that you can make better wines and that you will become a better winemaker?

“A better winemaker,” you ask? “I’m already making great wines.”

I always repeat my dad’s words of wisdom: “You are only as good (in your trade or hobby) as your ability to solve problems.” A wine with a pH out of control can soon turn bad.

So let’s take a look at why monitoring pH is important, how to control pH and make adjustments. First, a quick refresher on what pH is.

What is pH?

pH is a measure of the acidity (or alkalinity) of an aqueous solution, or, in winemaking, juice or wine. Whereas total acidity is a measure of the concentration of all acids in a solution, pH is a measure of the strength of acids; not all acids are equally strong.

Consider two solutions with the same concentration: Hydrochloric acid (HCl) and acetic acid (CH3COOH). Although the two have the same concentration, the hydrochloric acid solution is much, much stronger. That’s because the hydrogen atom in HCl dissociates much more readily than the hydrogen atom (the one in the COOH group) in acetic acid. And so, you would find a much greater concentration of dissociated hydrogen atoms in an HCl solution than in one of acetic acid.

pH is thus defined relative to the concentration of hydrogen atoms, and more precisely as the negative of the logarithm (to the base 10) of the hydrogen atom concentration in solution. The “negative” part of this definition is what confuses non-chemists. That’s because as acidity increases, pH decreases, and vice versa. For reference, freshly distilled water has a pH of 7. Solutions with a pH less than 7 are acidic and those with a pH greater than 7 are alkaline (or basic). Juice and wine pH are typically in the range 3–4.

Why is pH Important in Winemaking?

A low-pH wine will taste tart, owing to the higher acid concentration. Conversely, a high-pH wine will taste flat and lack freshness. However, the single most important aspect of pH in winemaking is that microbial stability and spoilage risks are highly correlated to pH. Microorganisms thrive at higher pH. With the less acidic environment, the winemaker needs to compensate with higher doses of sulfur dioxide (SO2) to keep those pesky devils in check. High-pH wines also tend to oxidize faster and therefore not age as well.

The ideal juice/wine pH range is 3.2—3.6. Because whites tend to have higher acidity, these will typically have lower pH than reds. That doesn’t mean that wines outside this range are subpar. There are many great wines with pH below 3 or above 4. As a winemaker, and this is important, you simply need to know how to work with juice and wine that are outside this ideal range.

For example, a red wine with a pH of 3.9 would require about 60 mg/L (ppm) of free SO2 to inhibit microorganisms whereas a similar wine but with a pH of 3.2 would only require about 13 mg/L. So right there, you can see that monitoring pH is an excellent strategy for determining how much sulfite is actually necessary to help protect the juice or wine. A handy sulfite calculator can be found at WineMaker Magazine to help you calculate sulfite additions.

As another example, bacteria used to conduct the malolactic fermentation (MLF) are sensitive to low pH and high SO2 levels. Malolactic bacteria generally need a pH above 3.2 and SO2 levels below 10 mg/L; these characteristics vary by bacterial strain.

And of course, along with total titratable acidity (TA), pH can confirm high or low acid levels and the gustatory impacts in a wine. Any deficiencies can be addressed by increasing acidity to decrease pH, and vice versa, reducing acidity to increase pH. The real value in monitoring pH here is the possibility of having to deal with the more challenging cases of high-TA/high-pH or low-TA/low-pH wines. We’ll come back to these.

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