It seems like a simple question and yet it’s actually a very complex one. For one thing, yeast are found about everywhere and there are thousands of different types of yeast. Should we therefore consider the yeast found on the apple as true cider yeast? What about the yeast found on the equipment used to process the apple? Is that the true cider yeast? What about if you inoculate with yeast? Does adding yeast make it not a cider yeast? Maybe you consider the wild yeast that creates a natural fermentation to be cider yeast. But, isn’t all yeast wild and natural? I did mention that this is a complex question. Let’s begin our journey to define cider yeast by first exploring the yeasts that are found on the apple or pear versus those found on processing equipment. Let’s also explore the concept of wild versus cultured or commercial yeast.
Fruit Versus Equipment
The yeast found on the fruit will vary from location to location. It may even vary from tree to tree. This is because yeast are affected by weather and can be transported by wind, insects, and animals. The one common aspect is that most yeast found on the fruit are non-Saccharomyces species. Some of the most common yeast found on apples are Hanseniaspora, Metschnikowia, Pichia, Candida, and Kloeckera species(1). Other yeast like Torulaspora and Brettanomyces have also been found.
You might notice a key yeast that is missing from this list is Saccharomyces cerevisiae. That is because, its not as common to find Saccharomyces yeast on fruit and if you do, the amount is usually quite low(2). Saccharomyces cerevisiae yeast is more commonly found on processing equipment and surfaces inside the cidery. This is because it appears that S. cerevisiae seems to have been domesticated by humans(3). In other words, it has evolved to be very efficient at living in environments constructed by us.
So, this begs the question, what would be natural cider yeast? Is it the yeast found on our fruit or the yeast found on our equipment?
Wild Versus Cultured
Many ciders and wines are made using a wild or natural fermentation process. In other words, yeast was not directly inoculated into the juice or must. But, is that true? Sure, you may not have opened a packet of yeast and pitched it into your juice but did you really not inoculate your juice? If fruit generally only has non-Saccharomyces strains of yeast and your cider finishes with Saccharomyces yeast as the dominate strain, how did it get there? Call it natural if you want but your equipment added that yeast or in other words, inoculated your juice. If you didn’t want that inoculation to occur, you would need to efficiently sanitize or even better, sterilize all equipment that could come in contact with your juice. If you don’t, you are inoculating it with the yeast it holds.
This brings up the other side of this question. What really is cultured yeast? Cultured yeast just means that a yeast cell (i.e. specific strain) was isolated and grown. Commercial yeast is cultured yeast. Someone identified a yeast strain that they really liked, isolated it, and grew billions of more cells. They then process and sell these to others. Sometimes, they even mix these strains together so you have a package with several pure strains in it. When you open that package and inoculate your juice with the yeast, you are simply adding strains with a known quality and performance. They are as natural as the yeast found on your fruit or your equipment. That is because they were found on someone’s fruit or equipment at some point in time. Note, there is a desire by some to genetically modify yeast but, GMO yeasts are not used for food preparation at this time.
So is natural cider yeast, only yeast found in the wild? If all yeast were originally found in the wild and most all ciders are inoculated with yeast through some means, what is natural cider yeast?
Natural Cider Yeast
As is common for me, the real answer to the question of what is cider yeast is that it depends. But, what it really depends on is you and your situation. Yeast will perform differently with different fruit and in different environments so what works for me, may not work for you. However, I will give you my view on what cider yeast is or at least what I think it should be. Though, my definition is still evolving as I learn more about yeast.
I believe true cider yeast are non-Saccharomyces strains. Also, we should be working to avoid inoculation of Saccharomyces cerevisiae yeast into our juice. That includes inoculation either by adding a packet or by exposing your juice to equipment with that culture on it. I believe the true cider yeast are the non-Saccharomyces strains that are commonly found on the fruit. You might notice that I didn’t say a wild ferment. I believe in inoculation of yeast so that you are targeting the characteristics you want. I feel that we have embraced Saccharomyces yeast too much and we have overlooked thousands of other possibilities. I am not dismissing the benefits that Saccharomyces strains have brought humans over the last several thousands of years. But, our technological advances should be driving us to explore more and not less options. The yeast used for beer and wine should not be the same as that for cider. Cider should begin returning to its roots or, to be more exact, its fruit.
My goal this year was to explore non-Saccharomyces strains of yeast so I acquired 11 strains of four different genera from the USDA. These were Lachancea thermotolarens, Hanseniaspora uvarum, Candida zemplinina, and Pichia kluyveri. Check out my initial research on these in other articles on the site and look for future articles on results. However, my preliminary findings are that all of these 11 strains produced good ciders. Yes, I have my favorites but the results have showed me that I can produce a dry cider or cider with natural residual sweetness by inoculating with different strains. I can give my cider fruity, banana, spicy, smoky, or phenolic aromas. I can also adjust the acidity by selecting different strains. If I can do this with just 11 of the thousands of different yeast strains out there in the world. What else is possible? Find out by exploring yeast. Culture your own or work with others to expand the true cider yeasts beyond Saccharomyces cerevisiae and those used for wine and beer. Cider yeast needs to be defined and developed. It’s not just about pressing your fruit and letting it ferment. There is science behind all this and its a science we have to tools to explore. All cider lovers should embrace understanding their yeast more so we can use this knowledge to guide cider’s future. This is the true cider yeast.
(1) V.K. Joshi and associates, Science and Technology of Fruit Wines: An Overview, 2017
(2) A. Aranda and associates, Molecular Wine Microbiology – Saccharomyces Yeasts I: Primary Fermentation, 2011
(3) A. Vaughan-Martini and A. Martini, The Yeasts, a Taxonomic Study, Chapter 61, 2003
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