What makes for a buttery wine?

Definitions:

There are many terms for the microbial action associate with “buttery wine”. This buttery mouth feel is a result of a chemical reaction facilitated by bacteris.

“Secondary fermentation” :This is often called “secondary fermentation”. Fermentation is a term better associated with the microbial process that turns sugar into alcohol. Here we are discussing a process that converts malic acid to lactic acid. 

Malolactic fermentation: Malic acid is associated with a sharp acidic or tart taste. Lactic acid, on the other hand, is associated with that smooth and buttery taste to the wine. If you look at the history it was not an intended part of the process. In the beginning it was thought to be a contaminant to avoid. Now, the process is recognized and even nurtured. A better term for this process is:

Decarboxylation: This chemical reaction is facilitated by bacteria. The malic acid is converted to lactic acid and carbon dioxide is released. Malic acid is associated with the sharp and tart taste. Lactic acid is milder and associated with the buttery mouth feel. This decarboxylation process we are focusing on is with the conversion of malic acid. There are more minor decarboxylations with other acid compounds and also associated with taste profiles but for this discussion we won’t go there.

Bacterium:

Primary fermentation utilizes yeast that convert the sugar to alcohol. The generic term for the bacterium used for decarboxylation of malic acid are generically known as lactobacillus. Some could enter the wine from a wild state where they could just be present in the air. The primary one used is Oenococcus oeni. Others used may be lactobacillus, Locunostock, or Pediococcus.

The process could be concurrent with the yeast fermentation but most commonly is done at the tail end of the yeast fermentation. They obviously can tolerate the alcohol created. They generally thrive more at a slightly higher temperature. pH is also a consideration and is monitored.

If you monitor the pH you would notice a higher pH or less acidity of the wine. Some chemical measures available to the wine maker are chromatography and even enzymatic assays Control measures may be needed to halt the process.

Examples and Benefits:

Most reds take advantage of the ability to decrease acidity and make the wine smoother. Not all whites would use malolactic decarboxylation. Chardonay likes that buttery mouth feel. Some whites rely on that acid aspect like Rieslings and avoid the malolactic conversion.

What lies ahead?

This process was discovered many years ago and thought to be an aspect of wine production to avoid. Many bottles were discarded. Now the process is understood and embraced in a more controlled manner. Perhaps there will be discoveries with currently unknown bacterium. Measures that drive or restrain the process will continue to be refined. The ability to monitor the process in real time with better analytic methods will add to the science.

At Familia Morgan Wine we let a gradual temperature of the wine rise to a target of 20-23 degrees Celsius. We are trying various inoculums provided by the Lafort company. We rely on the almost daily tasting by the winemaker to monitor what is going on. In addition to tasting he’s looking for the tiny CO2 bubbles produced when the bacteria are active. We use paper chromatography to assess. We’re expanding our lab with the addition to our bodega underway. Such is the art, the skill, and experience of the wine maker.  We don’t have a nearby lab that can assist with some of the highly technical assays for enzyme activity yet. Maybe we’ll have to do it ourselves in our lab? It’s coming. 

In our pursuit of making the best wine possible we’ll continue to hone our craft.

Barry Morgan M.D.

References:

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  2. Bartowsky E.J., Costello P.J., Chambers P.J. Emerging trends in the application of malolactic fermentation. Aust. J. Grape Wine Res. 2015;21:663–669. doi: 10.1111/ajgw.12185. - DOI
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  6. Molecular tools for the analysis of the microbiota involved in malolactic fermentation: from microbial diversity to selection of lactic acid bacteria of enological interest.Rivas GA, Valdés La Hens D, Delfederico L, Olguin N, Bravo-Ferrada BM, Tymczyszyn EE, Semorile L, Brizuela NS.World J Microbiol Biotechnol. 2022 Jan 6;38(2):19. doi: 10.1007/s11274-021-03205-0.PMID: 34989896
  7. Implications of new research and technologies for malolactic fermentation in wine. Sumby KM, Grbin PR, Jiranek V.Appl Microbiol Biotechnol. 2014 Oct;98(19):8111-32. doi: 10.1007/s00253-014-5976-0. Epub 2014 Aug 21.PMID: 25142694
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