Torulaspora delbrueckii Yeast and Stuff About It
As brewers, we have always been enamored with unique flavor and aroma profiles created by mixed fermentation brewing where multiple yeast and bacteria are working together simultaneously. Off Color’s pre-launch collaboration with Three Floyds, Tonnere Neige, mixed fermented wort with two classic saison yeast strains. Our first flagship Troublesome required us to bring in a Lactobacillus culture to acidify one beer to later blend into a Saccharomyces fermented beer. Since then, we’ve made countless small batch mixed fermentations, which usually consist of some combination of Saccharomyces, Lactobacillus, and Brettanomyces.
Our newest flagship beer Very, Very Far Belgian style ale adds a new twist to this mix fermentation lineage. Very, Very Far is mix fermented with a non-traditional wine yeast, Torulaspora delbrueckii (pronounced toe-rule-a-spore-a), and a Belgian ale strain. Our first experimentation with Torulaspora yeast goes back to early 2018 when a one off batch called Tiny Pillows was fermenting away. The beer served as our first fermentation study of Torulaspora delbrueckii as it was included in a mix fermentation with another known mixed culture we commonly use in a simple saison grain bill. The name Tiny Pillows originated from the fact that Torulaspora derives from the Latin word torus which means cushion or bed and, physiologically, Torulaspora yeast cells are roughly one third the size of Saccharomyces cells (the traditional yeast used in beer fermentation).
Domesticated Torulaspora yeast is limited in its ability to ferment beer as it cannot metabolize maltose, the main sugar contained in beer wort.* Because of this, domesticated Torulaspora yeasts will only create a partially fermented beer in standard brewers wort when mono-fermented. Once it metabolizes the sucrose, glucose, and fructose, fermentation halts. Torulaspora’s ability to ferment simple sugars but not common beer wort sugars is likely a reason it has found some use in wine but not beer. In order to complete fermentation and create a standard strength beer, the wort must be mixed fermented with a yeast that can metabolize higher chain sugars. This is not as easy as it sounds, as mutual inhibition exists between these two strains when competing for nutrients in the same beer wort.*
Our early trials of beers utilizing mixed fermentation including Torulaspora yeast featured unique notes of fruit cocktail, specifically lychee, papaya, apple, peach, apricot, and pineapple. Some of these fruit notes are uncommon in beer fermented with only Saccharomyces strains as they derive from certain types of ethyl esters, ethyl decanoate and ethyl dodecanoate. Ethyl esters come from the esterification (or combining reaction) of ethyl alcohol and medium chain fatty acids. Less important than how yeast makes these esters is the fruit and floral profile they can add to beer. Ethyl decanoate, an ethyl ester, has a much higher aroma threshold, lower concentration, and is transferred to the fermentation medium (beer) less completely than almost all other common beer esters, thereby is generally a small faction of beer aroma.** But beers mix fermented with Saccharomyces and Torulaspora yeasts have been shown to contain significantly more ethyl decanoate and ethyl dodecanoate.* By mix fermenting with these two yeasts, we can achieve unique fruity and floral flavor and aroma profiles.
To balance the fruit cocktail ester profile created by the Torulaspora yeast and to complete fermentation, we chose to mix ferment with a traditional Belgian Saccharomyces strain to add a peppercorn phenolic character. This specific mixed fermentation creates balance similar to the way a great hefeweizen balances banana esters (isoamyl acetate) and clove phenols (4-vinyl guaiacol). A hefe-belgo ale if you will (but you certainly don’t have to…and actually, don’t). Only through mixed fermentation and selecting these specific cultures are we able to create these unique and synergic fermentation flavors in the finished beer. And it goes really well with tacos!
*Toh, Darel & Chua, Jian Yong & Quan Liu, Shao. (2018). Impact of simultaneous fermentation with Saccharomyces cerevisiae and Torulaspora delbrueckii on volatile and non-volatile constituents in beer. LWT. 91. 10.1016/j.lwt.2018.01.025.
**S. M. G. Saerens, F. Delvaux, K. J. Verstrepen, P. Van Dijck, J. M. Thevelein, and F. R. Delvaux; Parameters Affecting Ethyl Ester Production by Saccharomyces cerevisiae during Fermentation; APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 2008, p. 454–461
