The bacteria in a Mosterra are specifically chosen to be hostile to one another. In the span of a few weeks, the bacteria wage a micro-war, producing unique topography-like structures as a result the chemical reactions produced during battle.
Most of these pieces are created in factories, where each dish is sterilized after the process so as to avoid remenant bacteria that could pose a risk to the dish owner. Mosterra enthusiasts (those who can afford it, at least) often buy the necessary ingredients and create their own versions. Naturally, many have suffered bacterial infections as a result of insufficient caution.