Acid Balance: Focus on MLF
Options for Acidification and De-acidification
1. Dilution for De-acidification
Grape wine: Dilution with water is not an option for most professional winemakers although it is dictated by country and regional wine appellation rules. Therefore, most grape winemakers will choose to blend or use other methods of increasing or decreasing acidity.
Fruit wine: It is generally acknowledged that fruit juice/fruit will require dilution. Fruit winemakers spend many hours calculating the correct ratio of fruit juice to water in order to achieve a stylistic acid balance. Each batch of fruit will have a different ratio which must be independently verified every time and is often a well-kept secret. Also, different varieties of the same fruit are treated differently; again, a winemaker’s diary and secrets of the trade as to how we manage those. I have also posted about the specifics of Haskap acids in the following link.
2. Natural Fruit Acids for Acidification and Chemicals for De-acidification
Some fruits and many grapes (particularly cold climate grapes) require further amendments to obtain a desirable acid balance.
Acidification: Generally speaking, acidification with tartaric and/or malic acids is considered acceptable in both grape and fruit wines. Depending on country and regional appellation rules (and good winemaking practice), citric acid may be used as well, although it is often banned. For example, bananas are very high pH with low acid level and will require some acid adjustments at crush. A winemaker may choose to use tartaric, malic, or citric acid (or a blend of any of them). All acids used in amendments for winemaking are usually obtained from natural fruit sources, and not chemically or artificially produced.
De-acidification: Two major chemicals used are potassium (bi)carbonate and calcium carbonate. Used correctly, this is a powerful tool in the winemaker’s arsenal to achieve acid balance. Again, bench trials will be necessary. The specifics of de-acidification are lengthy and beyond the scope of general discussion. Take a course if you want to learn more!
3. Malolactic Fermentation for De-acidification (MLF)
Malolactic Fermentation uses safely isolated bacteria found naturally in fruit and wine providing a species that will do the job of secondary fermentation without creating undesirable effects. For example, Oenococcus oeni is one of the lactic acid bacteria (LAB) which converts malic acid to lactic acid. In other words, if Malolactic Fermentation were allowed to progress ‘naturally’, the wine could develop several faults due to the action of undesirable LAB strains. We have chosen a specific commercial strain of LAB. There are many strains of LAB available which, like yeast, provide for specific secondary attributes and are chosen based on the stylistic goals of the winemaker.
Complete: Grapes and most fruits have at least a measure of malic acid in them. Malic acid levels will depend on variety, ripeness, climate variation and sunshine hours. Haskap have approximately 40% malic acid which can be changed through the action of malolactic bacteria to lactic acid, if desired. Lactic acid is often more desirable since it is less acidic, creates a smoother taste profile, and may assist in achieving the stylistic goals of the winemaker. Often, a wine is put through a complete MLF during which all the available malic acid is converted into lactic acid. In saying so, MLF may create other attributes, such as buttery profile which detracts from the fruit-forward character of Haskap wine. There are, however, methods of conducting MLF which decrease the undesirable attributes and accentuate the desirable ones.
Partial: Winemakers have the option to conduct a partial MLF in an effort to balance the taste profile. In other words, only part of the malic acid will be converted to lactic acid; when the desired profile is obtained, the lactic acid bacteria (LAB) are halted by one of several means, including filtration. I have chosen to attempt a partial MLF on Batches 2, 4, and 6. MLF is a lot less aggressive and takes longer than yeast primary fermentation. The bubbles are tiny. There are more parameters to monitor as well, but we’re hoping the end result will be worth the effort.
Batches 2, 4, and 6 will undergo partial MLF
4. Blending
Many wine batches have been saved by judicious blending with another of higher or lower acidity. Again, winemakers use bench trials to make these decisions. For example, if the titratable acidity (TA) of batch A is over the top (eg 11 g/L), and batch B is relatively low (eg 6 g/L), one could blend at a ratio of 1 part batch A: 4 parts batch B, in an effort to achieve a more palatable TA of 7.5 to 8 g/L. Since wine is an incredible buffer, the chemistry of this blend will not work out mathematically as one expects. Therefore, bench trials are in order.
New Terms
Appellation: An appellation is a legally defined and protected geographical indication used to identify where the grapes for a wine were grown. Many countries have dozens of appellations. The term is not used for fruit winemaking.
Buffer: The property of a substance to change the pH in ways you don’t expect or can’t mathematically predict due to the nature of that substance (weak acids and conjugate bases in the same solution or weak base and conjugate acid in the same solution). By its nature, wine is chemically very unpredictable and frequently buffers blending.