Fermentation Primer Lesson 9
From Sugar to Alcohol
Fermentation Primer - Lesson IX
In last month’s lesson we discussed how some yeast species have evolved the ability to produce killer toxins whose sole purpose is to kill other yeasts. We also discussed Pichia kluyveri, a yeast capable of producing higher than normal levels of ethyl acetate and iso-amyl alcohol.
Q: Can the same yeast employed in a traditional rum fermentation be also used in the preparation of high carboxylic acid blends, such as dunder?
P. Kluyveri yeast
Carboxylic acids are essential in the production of esters, and traditional yeasts like Sacharomyces Cerevisae typically produce only a limited amount of these acids, primarily in the form of etanoic (acetic) acid. Much in the same manner as sour mash whiskey is produced, high ester rum distillers have relied on fermentation ammendments designed to lower the pH of the wash. The most common example of this is found in Jamaica’s dunder. Let’s take a closer look at one yeast species that is showing a lot of potential in this area. Lachancea thermotolerans (previously known as Kluyveromyces thermotolerans) is a wildly-occuring species of fermenting yeast, comprised of hundreds of varieties/strains, most of which have only drawn the interest of scientists in recent years. Some of these strains, under the right environmental conditions, can achieve fermentations of up to 13.6% ABV.
Despite the ability to ferment to high ABV levels, one of the drawbacks of using L.
Correlation between Lactic Acid and PH Values
thermotolerans is that it is not able to produce complete fermentations, always leaving residual sugars. While this can be an issue in the beer or wine industries (where the solution is to use co-starters, such as S. cerevisiae), high-ester rum producers are less worried, since maintaining dunder pits requires the constant addition of fermentable sugars, typically in the form of molasses.Unlike S. cerevisiae, however, L. thermotolerans produces lactic acid at quite a high rate. The maximum reported lactic acid concentration is 16 grams per liter, compared to less than 0.4 grams of lactate per liter produced by S. cerevisiae (Banilas, G., Sgouros, G. & Nisiotou, A. Development of microsatellite markers for Lachancea thermotolerans typing and population structure of wine-associated isolates. Microbiol, 2016). As useful as it is for acidic fermentations in general, at present L. thermotolerans is primarily employed in the wine industry, where it offers a unique potential to counter the effect of global warming on wine grapes by producing acid during fermentation, which can moderately reduce alcohol levels while producing also high concentrations of desirable fruity flavor compounds, like ethyl lactate (using lactate as a precursor).
Join us again next month as we continue to explore this fascinating topic.