Why do some hard ciders become crystal clear in a few days while others seem to always have a slight haze? Have you ever had a hard cider that formed a film on top of it? Were you aware that the yeast you use might impact whether that happens? It all comes down to genetics. Yes, the genes found in your yeast impact the processing characteristics of your hard cider. As discussed in other Mālus Trivium posts, the Saccharomyces cerevisiae yeast DNA genome was sequenced in 1996 and about 6,000 genes were identified. In the book Science and Technology of Fruit Wines: An Overview(1), V. K. Joshi and associates summarized some of the key yeast genes. These key characteristics include how yeast impact processing characteristics including the following.
- Protein Haze – Proteins are amino acids linked in long chains. Yeasts break these down for nutrients and other compounds. Besides impacting fermentation rates and aromas, the proteins and amino acids that a yeast can process will impact potential protein haze. It has been found that some proteins more readily form haze versus others.
- Sediment & Flocculation – Some yeast will naturally “flock” or come together to form larger and heavier groupings of particles. Because they are heavier, they will naturally start to settle to the bottom of fermenters. This is great for creating clear hard ciders but, it has a negative impact related to fermentation. Yeast that precipitate out and settle to the bottom will die or at least become much less effective at fermenting. This can result in weak or stuck fermentation.
- Flor Formation – In wine, the formation of a biofilm on top can be a good thing. This is also called pellicle in beer brewing. It may not look pretty but yeast with these genes are actually protecting your precious cider from further oxygen degradation.
Here are some of the key aroma and sensory genes identified by V. K. Joshi and associates. I’ve used the UniProt.org site to note the roles these genes play in generating aromas and sensory characteristics.
- PEP4, END1, EXG1, CEL1, BGL1, PEL5, PEH1, XYN1-5, ABF2 – These genes impact the cell wall structure but also the ability of yeast to breakdown proteins. The ability of yeast to process proteins and release proteins can impact whether your cider could have a protein haze.
- FLO1, FLO5 – Flocculation is controlled by these genes. This defines how easily yeast can form larger groupings and precipitate out of suspension.
- MUC1, FLO11 – These genes are related to the creation of flor or in beer, pellicle. When exposed to oxygen, some yeast can create a biofilm that will protect the hard cider, wine, or beer. The ability to create this flor or biofilm is managed by these genes.
Here is another example of the importance that yeasts play in how you process your hard cider. The genes found within the specific strains you are using can impact how much protein haze you might have, how quickly your cider might clear, how well it might ferment, and whether it can produce protective biofilm. Knowing and understanding your yeast and whether they can breakdown proteins, flocculate, or form flor guides you in how you might need to process one hard cider differently from another.
(1) V.K. Joshi and associates, Science and Technology of Fruit Wines: An Overview, 2017
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