Q. Approaching bottling, I have a couple of carboys at pH 3.9 and 4.0, while others are at pH 3.26. I recently blended some early and late batches and got great results, but I’d rather not blend these because I’d like to preserve the individuality of the different grape varieties and vineyard regions. Is raising pH with potassium bicarbonate a good option at this stage? I’ve been warned against using it. Or should I get over my aversion to blending and just do it?
Jeff Sullivan
via email

A. This is one of those questions where I’d really like to ask one more thing before answering: Are these red wines or white wines?

That matters because the ideal pH range depends somewhat on the style of wine. Since I don’t know, I’ll answer in general terms.

The first thing that catches my eye is that these wines are living in very different neighborhoods chemically. A pH of 3.26 is fairly low for many red wines, while 3.9 and 4.0 are high for almost any table wine.

Let’s start with the low-pH wine.

If it’s a red, a pH of 3.26 may leave it tasting a little sharp or angular. In that case, potassium bicarbonate can be an excellent tool. It neutralizes a portion of the tartaric and other acids, allowing the pH to rise modestly while reducing total acidity. Despite the warnings you’ve heard, potassium bicarbonate isn’t something to shy away from necessarily. It’s a legitimate winemaking tool when it’s used for the right reason and in the right amount. The key is restraint.

Always perform bench trials before treating the entire batch. Small additions often make a big difference, and every wine responds a little differently because of the natural buffering capacity of each wine’s unique chemistry fingerprint.

Don’t bottle immediately after making a potassium bicarbonate addition. Give the wine at least a month to settle before racking off the potassium bitartrate crystals that form. That extra patience will reward you with a more stable wine, which will have less of a chance of throwing a sediment layer in the bottle later.

Now let’s look at those wines sitting at pH 3.9 and 4.0. Those numbers concern me more than the 3.26.

High-pH wines generally don’t age as gracefully. They are more susceptible to spoilage organisms, sulfur dioxide becomes less effective at protecting them, and they often require higher free SO₂ levels to achieve the same antimicrobial protection. They can also taste a little softer or less vibrant than wines with slightly lower pH.

For those wines, I definitely would not use potassium bicarbonate. In fact, I’d be thinking in the opposite direction.

If the wines taste balanced, a modest tartaric acid addition might be worth exploring through bench trials. Even bringing those pH values down into the neighborhood of 3.8 could improve microbial stability, make your sulfur dioxide program more effective, and give the wines a brighter, fresher profile for aging. As always, let your palate guide the final decision, not just the numbers.

Blending is another possibility, and one that’s often underestimated. Some of the world’s finest wines are blends precisely because one component fills in what another lacks. If your earlier blending trial was successful, don’t dismiss the idea simply because the wines came from different picks or vineyard blocks.

That said, I completely understand wanting to preserve each vineyard or variety on its own. There’s real satisfaction in bottling those personalities separately.

Fortunately, you don’t have to decide today.

Run bench trials with potassium bicarbonate on the low-pH wine. Try a few tartaric acid additions on the higher-pH wines. Then create several small blending trials and taste everything side by side. One approach usually begins to distinguish itself once the glasses are in front of you.

That’s one of the joys of home winemaking. You’re not committed until the cork goes in. The lab numbers provide important guidance, but they aren’t the final judges. Your palate should always get the last vote.

Good luck on the bench trials!