There are some common misconceptions about yeast. If you already know what it is not, skip past the teasers to the heading What is Yeast.
Is Yeast a Grain?
Yeast is not a grain. I guess the confusion here is that we so often hear that a gluten free diet an a yeast free diet are both the paths to a virtuous healthy life. Let’s not debate this here, other than to say the idea of everyone going gluten-free is debatable and only those who react to yeast need to avoid it, which is practically impossible anyhow, but if have this condition and you do your best, you will feel better.
Yeast and grain are frequently combined, especially in bread-making and beer.
Is Yeast Wheat?
No, see above. What is a specific type of grain.
Is Yeast a Plant?
Plants are multi-celled living things that you can see, and that turn sunlight into energy using photosynthesis, via chlorophyll. None of this describes yeast, so yeast is not a plant.
Is Yeast an Animal?
Animals, like plants, are made of many cells, although they cannot turn sunlight into energy. They can move around when they want to, at least until they become permanently attached to something, like for example when a barnacle attaches to a rock, although most of what most of us (rather than biologists and the like) would think of something with fur and four legs or feathers and two lets, or even something nasty with six legs as an animal. Perhaps the smallest animal, the tantulocarid Stygotantulus stocki, a type of crustacean, is only 0.0037 of an inch, which is way to small to see, but big enough to contain a sizable colony of yeasts, except for the hyper-large kind. All of this is far too complex to be anything like a yeast, so yeast is not an animal.
Is Yeast a Fungus?
Well actually, it is a type of fungus. It is a single-celled fungus, rather like a mold. There are other types of fungi that are more like plants, because they are made of lots of cells, for example the mushrooms you can buy in the supermarket, or very pretty ones, of all shapes and colours, that grow in the forest, but fungi are not like plants because they don’t make their own energy.
What Is Yeast?
As described above, yeast is a kind of single-celled fungus. There are 1,500 types identified, according to Wikipedia, although that is far too round a number to be exactly correct. Although single-celled, some form strings of cells, so they seem multi-cellular, however that is not what most people mean when they say the word yeast.
What they do mean is a small range of specific types of yeast. They almost always mean either Saccharomyces cerevisiae, the scientific name for baker’s yeast and brewer’s yeast, or Candida albicans, the nasty form responsible for yeast infection. The difference between baker’s yeast and brewer’s yeast is the strain (very closely related), so they are very similar. Just to be more correct but unfortunately more confusing, the kind of brewer’s yeast that is similar to baker’s yeast is used to make ales, where as Saccharomyces pastorianus, a (different sub-phyla, making it closely related, to baker’s yeast) is used to make lager.
I could go on to talk about yeasts used in wine but you get the idea. Different strains have slightly different characteristics, which can change the taste for example.