Scientifically, yeast are identified by a classification methodology. They are part of the fungi kingdom and they will have different families and orders(1). For alcoholic beverages makers, like hard cider makers, we usually focus and talk about three classifications for yeast. The first and highest level is the genus. Saccharomyces is a genus of yeast. We can use the plural form genera to describe all the various types of yeast genus used in making hard cider. This includes Saccharomyces but also Pichia, Lachancea, Candida, and others.
Below the genus is the classification we more often use. This classification is the yeast species. Saccharomyces cerevisiae is a species of yeast found within the Saccharomyces genus. Saccharomyces uvarum is a different species in the same Saccharomyces genus. The species classification provides a little more detail about a yeast. For example, we know that Saccharomyces cerevisiae yeasts are top fermenters that perform well in warmer temperatures while Saccharomyces uvarum species are bottom fermenters that will perform well at cooler temperatures. The species can be helpful but it doesn’t give cider makers enough detail. Not all Saccharomyces cerevisiae species are the same. For example, bread yeast is generally Saccharomyces cerevisiae but so are many beer and wine yeasts. Even yeast used to create biofuel is normally Saccharomyces cerevisiae. While all are Saccharomyces cerevisiae species, you can imagine that the performance characteristics would be quite different if you used them all to make cider.
As cider makers, the last classification is how we usually reference yeast, which is the strain or what is sometimes called type or breed. There are often tens of species within a genus but hundreds of strains within a species. I say hundreds but the reality is it could be an infinite number. We have 1500-2000 recognized species of yeast but a unique strain only needs a single change in its genetic code. One gene that is different can result in drastic changes in how a yeast performs. It’s these unique strains that we usually give names. EC-1118, Belle Saison, and Q23 are all brand names of unique yeast strains. They were isolated, propagated, and their performance characteristics defined. We haven’t started publishing the genetic DNA sequence of each yeast strain and how each gene impacts performance but I can imagine a world where the yeast specification sheet defines the genetic code and how it performs. In fact, I could envision being able to use a drop of juice and have a software program analyze it and select the best yeast given your desired characteristics. For now, we will have to live with specification sheets that provide an overview of the performance based on testing. If you review the sheets for EC-1118, Belle Saison, and Q23, you will find they are all from the Saccharomyces genus and Saccharomyces cerevisiae species. While they all share some characteristics, each of them create a unique flavor profile and have different fermentation performance. They each have a slightly different DNA structure.
As cider makers, the challenge we face is that most commercial yeast is dominated by one genus and even one species: Saccharomyces cerevisiae. Yes, you can find many strains that perform uniquely within this species but as I’ve noted in other articles, Saccharomyces cerevisiae is not the yeast most likely to be found living on fruit in nature. It’s found in human environments. There is no certainty about where it originated but, it dominates as the commercial yeast of choice because it tends to dominate over other yeast. However, research is showing that it may not be the ideal yeast in all situations(2) and I’d argue that it is far from ideal for cider. Let’s explore the genera of some yeast commonly found on apples(1).
Genus: Lachancea
Accepted Species:
- Lachancea cidri
- Lachancea fermentati
- Lachancea kluyveri
- Lachancea meyersii
- Lachancea thermotolerans
- Lachancea waltii
General Characteristics(1): Is usually spherical, ovoid, or slightly elongated in shape. Has a strong preference for glucose over other sugars. It prefers ethylamine as a nitrogen source.
Trialed Strains: I have trialed several Lachancea thermotolarens strains with positive results. L. thermotolarens is know to create lactic acid and even convert malic acid to lactic acid. This makes it a good choice for a souring yeast. One strain I have trialed showed signs of converting malic to lactic and another was unable to complete fermentation as it retained a few points of sugar.
Genus: Candida
Accepted Species:
- Candida aaseri
- Candida aglyptinia
- Candida akabanensis
- Candida alai
- Candida albicans
- Candida alimentaria
- …
- …
- Candida yuanshanicus
- Candida yuchorum
- Candida zemplinina
- Candida zeylanoides
General Characteristics(1): There are around 314 species in the Candida genus. But that seems to be regularly changing. A great example is Candida zemplinina, which has recently been identified as a new species called Starmerella.
Trialed Strains: I have trialed a couple strains of Candida zemplinina (Starmerella bacillaris). While slower fermenters, they both completed fermentation and generated smokey and spicy aromas.
Genus: Hanseniaspora
Accepted Species:
- Hanseniaspora clermontiae
- Hanseniaspora guilliermondii
- Hanseniaspora lachancei
- Hanseniaspora meyeri
- Hanseniaspora occidentalis
a. Hanseniaspora occidentalis
b. Hanseniaspora occidentalis - Hanseniaspora opuntiae
- Hanseniaspora osmophila
- Hanseniaspora pseudoguilliermondii
- Hanseniaspora uvarum
- Hanseniaspora valbyensis
- Hanseniaspora vineae
General Characteristics(1): There are 11 accepted species of the Hanseniaspora yeast genus. The cells shapes are often apiculate or elongated. They usually are low producers of acetic acid. They will not usually ferment maltose.
Trialed Strains: I have trialed three strains of the Hanseniaspora uvarum species. One strain had some residual sweetness while the other two completed fermentation. They were slower fermenters than Saccharomyces cerevisiae. The aroma was fruity with one that had strawberry notes.
Genus: Metschnikowia
Accepted Species:
- Metschnikowia aberdeeniae
- Metschnikowia agaves
- Metschnikowia andauensis
- Metschnikowia arizonensis
- Metschnikowia australis
- …
- …
- Metschnikowia sinensis
- Metschnikowia vanudenii
- Metschnikowia viticola
- Metschnikowia zizyphicola
- Metschnikowia zobellii
General Characteristics(1): There are 39 accepted species of Metschnikowia yeast. The yeast ranges from spherical and ellipsoid to pyriform, cylindroid, or lunate. Many will form long term tubes during reproduction. Most species will ferment maltose.
Trialed Strains: I have not yet tested any isolated strains from this genus but, I’m working to address that.
The world is full of yeast. Not every fermentation needs to be conducted with the Saccharomyces genus. We should all be exploring other genera of yeast and trialing unique strains for cider. There are cider yeasts out there. We just have to find and isolate them. Join me in exploring new yeast and make sure you share what you find with the rest of us. Check The Shop if you are interested in trying some of the yeasts I’ve been exploring.
(1) C. P. Kurtzman and associates, The Yeast: A Taxonomic Study, Chapter 1, 2011
(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
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