Balancing Acidity in Minnesota Wines: Techniques and Strategies for Winemakers

Before grapes arrive in the winery, allowing fruit clusters to ripen fully in the vineyard is essential to decreasing acidity. As grapes ripen, the acids generally decrease while the pH rises. Deciding to pick grapes too early will exacerbate the issue of high acidity and low pH. It is essential to give the crop time to ripen fully, and give attention to how the grapes are sampled and tested. 

Grape sampling and juice analysis videos:

Most cold climate interspecific hybrid cultivars can hang on the vine for an extended ripening period due to having thicker skins and looser clusters. However, there are other issues that are not always under one’s control, including unfavorable weather events (e.g., excessive rain, hail, or early frosts), high insect pest and/or disease pressure, as well as labor and equipment availability for harvest. An early harvest may be necessary, but when possible, allowing the fruit to sufficiently ripen will help ensure that the acidity and pH reach preferred levels.

Calcium carbonate, potassium carbonate, and potassium bicarbonate are a few compounds that can de-acidify grape must by neutralizing and precipitating tartaric acid. 

Article 

The link below leads to an informative article from Washington State University on the science and methods behind these techniques:

Link for WSU article on managing high acidity

A few things should be considered when using carbonate deacidification. The timing of these additions is important. It is best to deacidify prior to the start of yeast fermentation. Another important consideration is that—depending on the dosage rate—the use of these compounds can negatively impact wines by muting and/or altering the aroma, flavor, and mouthfeel. Thus, most winemakers prefer alternative methods to address high acidity.

Some winemakers scoff at the notion of adding water to their wine musts. There is no doubt, however, that balanced water additions can lower acidity and sometimes raise pH without loss or dilution of color, flavor, or character, even though it will lower the Brix content slightly. This practice is more widely used than most consumers are aware of and many winemakers might admit, but the use of water amelioration is allowable under federal regulations:

 “…In producing natural wine from juice having a fixed acid level exceeding 5.0 grams per liter, the winemaker may adjust the fixed acid level by adding ameliorating material…” -Code of Federal Regulations, Title 27, Part 24.178

The quality of water used is important for this process. Treated and/or filtered well water is usually fine, but it is still best practice to have the water quality checked for contaminants once every year. Excess iron is a particular challenge because it causes staining and has a bitter, metallic taste. City supplied water can also be a problem because most municipal water contains chlorine, which should not be used in wine making, as it can lead to the production of chloroanisole - a phenolic compound that taints wines. 

Article 

To learn more about how chlorinated water impacts wine quality, view this bulletin from Purdue University: 

Purdue bulletin on chlorinated water and wine quality 

Example: For a practical example on the use of water for amelioration, an addition of 6.8 gallons of water to 100 gallons of must will decrease the Brix from 26 to 24.5 and lower the total acidity by approximately 0.4 g/L. The addition of water may not end up being the primary and sole approach to adjust for high acidity but it can be considered an additional tool in a winemaker’s toolkit. 

One of the most effective ways to help balance high acidity is the yeast used for primary fermentation. There are quite a few strains that help to metabolize excess malic acid and lower total acidity. These include yeasts Lallemand 71B, VRB, SVG and Exotics Mosaics, which can lower acidity from 25% to 40% depending on which one is used. Maurivin B from AB Biotek claims to reduce malic acid by over 50%.

There are also other yeast strains that produce low or no H₂S and can help ensure a balanced or enhanced mouthfeel, producing fruit forward wines with lower production of acetaldehyde during fermentation, with additional improvement of fruit expression. Some of these from Lallemand include PERSY, SENSY, IOC BE FRUITS and IOC OPALE 2.0. Though these yeasts are not as efficient at metabolizing high acidity as the previous choices mentioned, their attributes used in conjunction with other techniques can assist in cleaner fermentations, and produce high quality and more balanced wines.

Secondary or malolactic fermentation (MLF) will go a long way to reduce wine acidity. It is a quality and style choice made based on the wine to be produced. Most red wines can benefit from MLF while white wines are typically discouraged from going through MLF. When conducted with experience and intention, complete or partial MLF in white wines can add greatly to the wine’s softer texture, increased complexity and nuance.

Malolactic bacteria (MLB) like a warm environment (i.e., temperatures between 65F-75F) and dislike high alcohol levels. A sequential addition of MLB 24-72 hours after the primary yeast addition can help ensure completion of MLF and make the wine inherently more stable post-fermentation and during the bulk maturation period in barrel or tank. It should be noted that adding MLB earlier (at or just after yeast addition) can produce less diacetyl which can give a buttery character to the wine, adding MLB later (after yeast fermentation) can produce more diacetyl character.

Paper chromatography testing is quick and easy to do, and can help you to know when MLF has finished.  A complete kit is available on various retail sites. 

Every winemaker should be aware that “traditional” cold-contact treatments for cold-stability can lower total acidity by precipitating excess tartaric acid crystals from a solution in the form of potassium bitartrate (i.e., KHT). However, it should also be noted that if a wine’s pH is above 3.65, the pH will rise during cold-contact stabilization and may be less protected from microbial spoilage.

Recently developed products like “Zenith” (potassium polyaspartate, also known as KPA) can ensure almost instant cold-stability in filtered wine, but these products do not have the effect of lowering excess acidity that can be expected from cold-contact methods.

After a winemaker has succeeded in producing a spectrum of quality varietal wines, the most creative skill and talent to be mastered is blending. Blending a high acidity wine with a low acidity wine will reduce total acidity in the final, blended wine.  Federal laws allow for blending up to 25% into a varietally-labeled wine, and the use of blending for various reasons, including for better color, balance, tannin, and increased complexity have their established tradition, history, and legal use in winemaking. The choice to blend is another optional and useful tool in the winemaker’s toolkit.

The addition of sweetening material to wine does not actually lower acidity, but it can help mollify, or take the edge off high acidity. There is more than one way to sweeten.

Table sugar (sucrose)

Table sugar (sucrose) works well to sweeten wine, and it does not matter if the sugar is made from cane, corn, or beets. However, it should be noted that when adding sucrose, eventually—in a few weeks or months—the glucose and fructose that make up sucrose will ‘cleave' and the perception of sweetness may increase slightly. 

Sweet reserves and other grape juice sources

An alternative is to use a “sweet reserve”, i.e., unfermented juice saved from the initial pressing of grapes, which is usually stored frozen until it is utilized. Sweet reserve additions advantageously have the original ratio of glucose and fructose as well as the original flavor and aroma compounds which can add to the character of the finished wine. Another option is to use pasteurized grape juice concentrate to sweeten wine since they have the similar advantages to a true sweet reserve. 

There are several winemaking products, adjuncts and processing techniques that can help soften the texture of high acidity wines even though they do not directly lower acidity:

• Oenolees and Powerlees are examples of specific yeast hull preparations that can aid in reducing bitterness and astringency and help to create a softer mid-palate profile that can elevate a perception of smoothness or even sweetness. 
• Scott Labs has a product called ULTIMA SOFT, made from mannoproteins and gum Arabic, that can also lower astringency and enhance the body, and create a rounder mid-palate. 
• Finishing tannins can have beneficial effects as well, especially when considering that Marquette and Frontenac wines seem not to retain adequate levels of tannin. 

• The technique of using 50% whole-cluster fermentation for Midwest red wines has also been shown experimentally and commercially to create richer and smoother wines preferred by consumers.

  Resources for adjuncts and other techniques 

• Yeast hull products (linked) 
• ULTIMA SOFT (linked) 
• Finishing tannins (linked) 
• 50% whole-cluster fermentation article (linked)