Alternative Cider Yeast: Starmerella bacillaris (Candida zemplinina) Overview

Originally isolated from grapes in California in 2002 and classified as Candida zemplinina in 2003. It was later changed to Starmerella bacillaris. The two samples I obtained from the USDA were logged under Candida zemplinina. Like many yeast, the advent of DNA sequencing has helped better classify many different yeast strains. However, recognize that you might need to look up both names if you are looking for strains or research on this yeast genus. As I did with my other posts on alternative yeasts, I plan to highlight the biochemical traits and fermentation kinematics. It’s another exciting alternative yeast option for making hard cider.

M. Lorenzini and associates found that Starmerella bacillaris didn’t consume all the available glucose and fructose(2) and Mills and associates found that it fermented fructose but not the glucose(3). Most research notes that it is highly fructophilic, meaning it likes fructose. If you remember in my Mālus Trivum on sugar, the top sugar in apples is fructose so it makes it an interesting yeast to explore. It is often noted that unlike many other non-Saccharomyces yeasts, Starmerella bacillaris is still found at the end of fermentation. Making it a good survivor and why it made my list of yeasts to explore this season.

Candida zemplinina Yeast sample from the USDA.
Candida zemplinina Yeast sample from the USDA.

Biochemical Traits

Starmerella bacillaris has often been found on grapes but as noted by J. Wei and associates, it has also been found on apples(2) and even prickly pears. It appears to generally be found on fruit and fruit flys. S. bacillaris is considered highly fructophilic but not as efficient in fermenting ethanol as Saccharomyces cerevisiae so it would naturally produce lower alcohol levels. S. bacillaris was found to decrease oxalis acid and malic acid. J. Wei and associates found that like Lachancea thermotolerans, it can metabolize malic acid(4). However, S. bacillaris is a producer of succinic acid, which at high levels can create salty or bitter notes. However, it appears to not generate large amounts of acetic acid though slightly higher than the Saccharomyces genus(1). As is common with many non-Saccharomyces yeasts, S. bacillaris was found to contain unique enzymes that allowed it to liberate the various nutrients it needed(1).

S. bacillaris is generally still found in wine at the end of fermentation, which means it can survive co-fermentation with more dominate or killer yeast genera. That is not the same for many of the other alternative yeasts I am planning to assess. This yeast has also been shown to grow at a wide range of temperatures but of interest to some might be its capability to ferment as low as 10C (50F). It’s ability to survive to the end of fermentation also indicates its tolerance to higher alcohol levels. It did appears to be inhibited by concentrations of 50mg/l or more of SO2, which indicates it may not be suitable for use with treatments of sulfite or Campden. I did not find any references to its ability to act as a biological agent in the treatment of spoilage organism.

My Interest: A yeast naturally found in abundance on apples and fruit that loves fructose and could reduce malic levels sounds interesting enough. While I will ferment warm, 72F (22C), it is interesting that it might work well at cold temperatures is interesting as it would be more universal for all cider makers. I also am intrigued by alternative yeast’s potential abilities to generate the nutrients it needs. I wonder how much we really need nutrients and what they really do. Given Saccharomyces cerevisiae is not an abundant yeast found on apples, it’s use and the perception of its needs for nutrients seem like we might be forcing the process. It will be interesting to see if it reduces the malic acid levels, something that would be good for those of us with an abundance of culinary apples.

Fermentation Kinetics

S. bacillaris will utilize all the fructose, which is different from other alternative yeasts that I am assessing like Hanseniaspora uvarum or Pichia kluyveri that will generally have some residual fructose at the end of fermentation. S. bacillaris tends to not process glucose as well and will have higher residual levels of this sugar that should create a natural residual sweetness. The one exception I found in my research was with some pear juice where S. bacillaris had more residual fructose versus glucose(4). One very positive fermentation characteristic of S. bacillaris is the level of glycerol it produces. It has been found to provide an abundance by several studies. Glycerol provide improved mouthfeel and some natural residual sweetness similar to sorbitol. S. bacillaris also appears to ferment slower than Saccharomyces yeasts.

The one potential downside to Starmerella bacillaris is that it seems to produce the lowest levels of volatile compounds so it might not have the aromas and flavors that other alternatives yeast can generate. These compounds generally include esters, aldehydes, and terpenes. S. bacillaris generated propanoic acid, 2-methyl-, and ethyl ester but did not see the increases that other alternative yeast did for key volatiles like 1-butanol, 3-methyl-, acetate, acetic acid, and hexyl esters, which create a banana aroma(4).

My Interest: My main goal continues to be finding a yeast or combination of yeasts that leave some natural residual sweetness in my hard ciders and Starmerella bacillaris is a strong contender. Given its glycerol production, even if it doesn’t dominate the fermentation, it still may contribute positively to a naturally sweeter hard cider. The risks appear that it may not be as flavorful as it doesn’t have the ester and volatile compounds production of other alternatives yeasts.

Sources

I have not found any commercial offerings of Candida zemplinina or Starmerella bacillaris on the market. This means you will need to try to find them through various culture collections, which are usually operated by universities or government agencies. I obtained two strains, YB-370 and YB-374 from the NRRL Culture Collection at the USDA. They only had three listed and did not have any yeast strains under Starmerella bacillaris so these might be harder to located. I know there are other culture collections around the world but these are the ones with websites I have found and you can explore. If you know of others, please send me a link.

(1) V. Englezos and associates, Exploitation of the non-Saccharomyces yeast Starmerella bacillaris (synonym Candida zemplinina) in wine fermentation: Physiological and molecular characterizations, International Journal of Food Microbiology 199 33–40, 2015

(2) M. Lorenzini and associates, Assessment of yeasts for apple juice fermentation and production of cider volatile compounds,  LWT – Food Science and Technology 99, 224–230, 2019

(3) D.A. Mills and associates, Yeast diversity and persistence in botrytis
affected wine fermentations, Appl. Environ. Microbiol. 68, 4884–4893, 2002

(4) 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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