Pichia kluyveri is found on many types of fruit but also on the fleshy part of the plant(1). Several isolated strains came from prickly pears in Arizona and California, which I appreciate given where I currently live. However, it was also isolated from olives and is very common on apples as well as coffee. It will generally always be part of any wild ferment you might do with apple juice no matter where you live. I obtained 3 samples from the USDA. In an assessment of 8 non-Saccharomyces strains, P. Kluyveri was chosen by panelist as the best fermenter of apple juice and specifically, Fuji apple juice(2). This was because it was shown to produce high levels of tropical fruit aromas. Like many yeast, it was originally known under another name, Hansenula kluyveri. Let’s explore some of the biochemical traits and fermentation kinematics of the genera of yeast.
Volatile compounds are one of the main characteristics of Pichia kluyveri and specifically, thiols that create tropical and passion fruit aromas. As noted in research performed by J. Wei and associates, their strain of Pichia kluyveri yeast was characterized by tropical and kernel fruit. The most common compounds were acetates 1-butanol and 3-methyl- along with hexyl and pentyl esters formed from acetic acid. Compared to other non-Saccharomyces yeasts, Pichia Kluyveri was the only one able to produce compounds like butanoic acid and the ethyl ester 3-methyl- in cider. P. kluyveri demonstrated a significant amount of lactic acid production, which is created during fermentation. Another interesting aspect of Pichia spp. of yeast is that they tend to prefer aerobic environments. This may tie to both their positive aroma contribution and to their low fermentation ability.
My Interest: A yeast naturally found on apples and in most wild hard cider ferments seems like the perfect yeast to trial. The ability of P. kluyveri to create strong fruity ester production sounds like another great reason to trial it for hard cider. It has also shown that it creates lactic acid. I couldn’t find data like Lachancea thermotolarens that indicate an ability to convert malic acid to lactic acid. However, since L. thermotolarens is mostly noted for producing lactic acid in low acid grapes, I am wondering if P. kluyveri is similar in that it will reduce the total acids in high acid apple juice during fermentation. That’s a third good reason to trial it. It could help reduce the acid found in many dessert and culinary apples.
Pichia kluyveri will ferment more glucose than yeast like Starmerella bacillaris. However, it’s ability to ferment fructose is the lowest of the 4 non-Saccharomyces genera that I plan to evaluate it’s the lowest producer of ethanol. It should therefore have the highest residual sweetness. In fact, while S. bacillaris is considered fructophilic, P. kluyveri is consider glucophilic(2). This simply means it prefers glucose. Overall, it is considered a weak fermenter and while it will survive in various temperatures, cold will slow the process even more. It is a good producer of glycerol in most apple and pear juices. This is positive as it will contribute more residual sweetness and mouthfeel.
My Interest: Pichia kluyveri may not ferment enough sugar and create enough alcohol to actually be an acceptable single yeast fermenter. This will make it an interesting and maybe challenging yeast to trial. If I was betting, this is the yeast that may not be able to outcompete the natural microflora. However, that is part of what I want to assess. I hope it will ferment and stabilize the cider with some residual sweetness but it does need to ferment enough so I really want to assess this aspect. However, it may be an ideal yeast to mix with other non-Saccharomyces strains to create a fruity and flavorful hard cider.
Like Lachancea thermototlarens, you can actually get Pichia kluyveri from a commercial source. CHR Hansen offers Frootzen, which is a Pichia kluyveri strain isolated from New Zealand grape juice. As stated on the CHR Hansen website, Frootzen should only be able to ferment 4-5% ABV. However, it has the highest volatile thiol production of any other yeast. These thiols are what create tropical and passion fruit aromas. Sounds like the perfect yeast for making cider. As noted above, my strains came from the USDA’s ARS Culture Collection. I obtained three unique variants for my trials, which were reference numbers Y-17774, Y-11519, and Y-17228. Maybe other yeast manufacturers will follow suit and bring some P. kluyveri strains to the market. However, I plan to plate mine for future uses and trials in the event I get positive results. I am sure you could find other P. kluyveri strains at other culture collections, like the NCYC in the UK. If you find some, please leave a comment and link below!
(1) C. P. Kurtzman, The Yeasts, a Taxonomic Study, Chapter 57, 2003
(2) J. Wei and associates, Characteristic fruit wine production via reciprocal selection of juice and non-Saccharomyces species, Food Microbiology 79, 66–74, 2019
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