What are mannoproteins and why would they be important to hard cider? Mannoproteins are a combination of polysaccharides and proteins bound up in the yeast cell wall. They are connected to the cell membrane that surrounds the yeast. This membrane retains all the key parts of a yeast cell like the nucleus, organelles, and cytoplasm. The mannoproteins are bound into the outer cell wall made up of B-glucan and chitin. Yeast cells will shed mannoproteins during fermentation as well as during yeast autolysis. Autolysis occurs when yeast die and breakdown, think aging on lees. The autolysis process releases various compounds found inside the yeast cell, including mannoproteins.
So, what do mannoproteins do and why are they important for hard cider making? I mentioned that they are a compound made up of mostly polysaccharides with a smaller amount of proteins. Polysaccharides are carbohydrates like starches that can be broken down for energy or structural polysaccharides like cellulose, chitin, and pectin. Proteins contain many different compounds like amino acids, enzymes, and antibodies. These compounds can be beneficial for activities like Malolactic Fermentation (MLF) but they can also provide other beneficial sensory characteristic for wine and cider. As noted by P. Domizio and associates, mannoproteins can improve mouthfeel, increase sweetness, add aromatic complexity, and improve stabilization in wine(1). It does this through the carbohydrates and proteins the mannoproteins release. For example, those proteins can support better foam retention in sparkling ciders and wines. Overall, you want more mannoproteins in your hard cider. How do you increase the mannoproteins?
One of the best ways to generate more mannoproteins in your hard cider is by using non-Saccharomyces yeast strains. Researchers are finding that non-Saccharomyces yeast strains create more complex aromatic compounds in cider and wine and one of those reasons is because they increase the amount of mannoproteins released during fermentation. P. Domizio and associates found that the 8 non-Saccharomyces yeasts they tested all generated significantly more mannoproteins than the commonly used commercial Saccharomyces yeast, EC-1118. One reason this happens is because non-Saccaromyces strains appear to turnover their cell wall structure much more readily during the growth phase, something most Saccharomyces spp. do not do.
(1) P. Domizio and associates, Use of non-Saccharomyces wine yeasts as novel sources of mannoproteins in wine, Food Microbiology 43, 5e15, 2014
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