Morphology simply means the form or structure of a plant or organism. Yeast morphology in this context is the shape of yeast cells. You may be surprised to learn that not all yeast cells are shaped the same. As a cider maker, if you assess your yeast under a microscope, you will generally find that yeast have different shapes. With hundreds or even thousands of potential yeasts strains, the shape won’t provide exact identification but it can give you an indicator of the potential classification. Generally, yeast will have three main shapes or morphologies. These shales are generally round (spherical), apiculate (oblate), and elongated (rod).
- Round: Saccharomyces cerevisiae generally have round or spherical shaped cells but not always. Other yeasts genera commonly have round shapes as well so you can’t be certain that any round shaped yeast are Saccharomyces species. You also can’t be certain that all round yeast are beneficial but, round cells are the most common shape cider makers will find, especially if you inoculate with commercial strains. Finding a large number of non-round cells could indicate other yeasts are present.
- Apiculate: Apiculate yeasts will look like a lemon or a flattened sphere (oblate). Many non-Saccharomyces yeast genera have apiculate shapes. Some of the most common are Hanseniaspora and Kloechera species. Pichia species also tend to be more oblate or even elongated versus round. If you are using a wild or natural fermentation, culturing and reviewing the yeast in your cider will most likely show a larger number or apiculate and oblate yeast cells.
- Elongated: Elongated yeast cells can look like rods or long cylinders. The most common types of elongated yeast cells are Brettanomyces and Candida species. While not all of these are spoilage yeast and not all spoilage yeast are elongated, finding a significant amount of elongated yeast in your cider, could indicate concern. If the cider has some faults, it would also point to a potential cause.
Assessing the morphology of your yeast won’t tell you the exact types of yeast present in your cider. But, it can help point you to a potential cause if your cider has faults or you have a natural ferment that has some interesting characteristics. A microscope and some plates can give you a quick assessment of your microflora and help point you towards the answer to your question. It can also help you select and isolate various strains for propagation. Interesting in plates or tools to harvest and culture yeast, check out The Shop to see what I use.
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