Yeast is actually a popular organism to work with for scientists. This is probably originally due to its value in making alcohol products and breads. Generally speaking, if your yeast are growing rapidly you are probably going to produce a lot of carbon dioxide. Yeast, just like humans, need a wide variety of different nutrients to survive and grow. When making bread, those nutrients generally come from the wheat flour. When scientists grow yeast, they will generally use a “broth” consisting of amino acids, salts (not just table salt), and a sugar (usually glucose). Interestingly enough, sometimes the broth for yeast will contain dried up yeast called yeast extract. Scientific-grade broth is pretty expensive though probably many of the components in the broth can be found in the vitamin and supplement aisle in a pharmacy such as in protein powder. Though I don’t really know in practice how effectively yeast will grow in products designed for humans.