Paul Santoriello’s Advice on Lowering Acidity in Cool Climate Grapes

Recently, my family had the privilege of receiving a behind-the scenes tour of the Peninsula Winery/Distillery located just north of Sturgeon Bay in Door County. Our tour guide was Paul Santoriello, the chief winemaker.

Paul Santoriello of Peninsula Winery in Door County

Paul is a California native who was educated in plant biology, soil science and viticulture at the University of California at Davis. Prior to assuming his duties at Door Peninsula Winery five years ago, Paul worked for the David Bruce Winery in Los Gatos, E. & J. Gallo in Modesto, and The Wine Lab in Napa.

Although about 85 percent of the wine produced at Door Peninsula Winery is fruit wine, the purpose of our tour was to learn more about the cold-climate grape wines produced and sold there. Some of the vines Door Peninsula Winery has chosen to cultivate are Marechal Foch, Vidal Blanc, Seyval Blanc, and LaCrosse. Like all cold-climate grapes, the Foch, Vidal, Seyval, and LaCrosse grapes often have high acidity, something that can pose problems for the winemaker who seeks to produce wine that others are eager to consume.

As we toured the winery’s fermenting room, Paul filled two wine glasses with Marechal Foch and handed me one to taste. As I was swirling my wine in the glass, I noticed out of the  corner of my eye Paul dropping a pinch of white powder into his glass. My first immediate thought (I have a very vivid imagination) was that Paul was a winemaker who actually was allergic to wine and was secretly trying to administer an antidote to himself before drinking the wine so that he didn’t begin convulsing in our presence. Yet what he was really doing was setting up a wine de-acidification test for my benefit.

My Foch wine (without that mysterious white powder dropped into it) tasted fruity yet acidic. Paul then handed me his glass and asked me to taste compare; it was much smoother tasting, now had a hint of oak flavor, and was more pleasing to the palette. What magical powder had this winemaker used to instantly transform this wine into a more pleasing, less acidic beverage? Paul ushered me over to a cardboard box enclosing a large plastic bag that contained this mysterious white powder: potassium bicarbonate.

Tasting Marchal Foch

Paul proceeded to inform us that at Door Peninsula Winery he cannot reduce the acidity of his Marechal Foch by inoculating it with malolactic bacteria because doing so would very likely infect the fruit wines produced in this same fermenting room with the malolactic bacteria, producing off-flavors in these wines. Paul’s solution is to reduce acidity in the Marechal Foch with the judicious use of potassium bicarbonate.

Paul told us that he had not de-acidified the Foch prior to fermentation because it already had a good flavor (although perhaps sharp) and that in the course of primary fermentation, acids often decrease on their own, and later cold stabilization often further reduces acidity. For those reasons he initially adopted a ‘hands off” approach to see if the Foch acid problem would self-correct, but as our taste test had just demonstrated, a small acid reduction at this stage did appear necessary.

Peninsula Winery and Distillery, Sturgeon Bay, Wisconsin

As we left the fermenting area, Paul stated that there are many benefits to de-acidifying high-acid wines, and that the ‘fat and thick” oak-aged, high pH/low acid wines currently so popular in the marketplace are walking a dangerously high wire in trying to find that delicate balance between proper acidity and rich flavor fullness. This is not necessarily a bad philosophy for winemaking, Paul stated, but when your wine pH approaches 3.6 you open your wine up to massive pressure from wine spoilage microbes. It is that very danger that makes sufficient acidity an essential factor in creating a healthy wine.

As we were talking, the thought occurred to me that it is likely that a number of  people who make wine from cold-climate grapes also make fruit wines in the same work area, and thus, face the same hazards from using malolactic cultures that Paul was describing. Another thought was that some of the cold-climate grapes may sometimes be so high in acid that deacidification prior to adding the yeast may be an absolutely essential first step in promoting healthy fermentation. The end result of our tour and the insights provided by Paul was the information about using powdered carbonates to reduce acidity in cold-climate wines.

When you have high acid/low pH must, it is best to de-acidify with potassium carbonates or potassium bicarbonates. This method works by combining with tartaric acid to form potassium bitartrate. Chilling the must before adding the potassium carbonates or potassium bicarbonates will aid de-acidification. Secondary de-acidification during wine stabilization is an added benefit of this method.

You can also use potassium carbonate or bicarbonate to raise wine pH after fermentation, because a higher pH wine will balance the acidity, it will shift equilibrium to favor tartrate stabilization, and it can also encourage a malolactic fermentation to further de-acidify the wine (if you decide to add the malolactic culture at the end of the active fermentation process.)

When you have high acid/high pH must, it is best to de-acidify with calcium carbonate. The method works by the calcium carbonate combining with tartaric acid to form calcium tartrate. Calcium carbonate can reduce tartaric acid on average by 5.0 grams/liter (0.5%) without affecting wine quality. It appears that the maximum benefit is obtained by splitting apart your total must into thirds, treating one-third with the calcium carbonate and then blending treated and untreated must portions. The must will continue to drop acidity, but to a lesser degree, during fermentation.

There is no problem with having calcium tartrate precipitation in your wine because you can simply rack it out. Most experts recommend using this method of de-acidificationearly in the winemaking process because must is more forgiving than wine.

In discussing the use of powdered carbonates to reduce acidity in cold-climate grape must or fermented wine, Paul was quick to point out that doing so only shifts pH and total acidity and does not eliminate malic acid, which is the primary reason for conducting malolactic fermentation.

As Paul told us, by transforming malic acid into lactic acid, Oenococcus microbes add complexity to your wine, but you need to carefully manage these microbes because they are living organisms and may not produce desired results every year. When working with Lisa Van de Water, a research expert in wine microbiology at the Wine Lab in Napa, Paul said that she regularly reminded him of something that is sometimes overlooked by winemakers; every year is different, and therefore, juice needs analysis every year.

Paul’s advice to winemakers is to never do the same thing to your wine each year with the expectation that it will yield the same result. And when you attempt to de-acidify your wine, remember that while doing so, you and your wine are walking on that high wire, and you need to be very careful that you don’t take too large of a de-acidifying step and cause your wine to fatally tumble to its death.

So, if I could summarize winemaker Paul Santoriello’s take-home message it would be, ‘While practicing the high-wire act of winemaking, finding the proper balance should always be uppermost in your mind.”

Dr. Stephen Franzoi is the editor of the The Vintner’s Press, a publication of the Milwaukee-based Wisconsin Vintners Association.   For more information, please see Vintner’s Press Articles on the Milwaukee Vintners Association website.