Yeast is probably familiar to most of you. It is responsible for making bread rise. It ferments barley into beer. There is nothing bad about yeast...but how many people know what, exactly, yeast is?
What? That's what yeast looks like beneath a microscope.
The grainy packet added to make bread rise is actually a fungus (Saccharomyces cerevisiae) waiting to feed on the delicious sugars in bread dough. Bread is mostly long chains of sugar, meaning that anything that can handle glucose can usually handle bread. Yeasts like the abundance of sugar in the dough and convert said sugar into CO2 and alcohol. Yes, there was once booze in your bread.
S. cerevisiae is also responsible for making beer. Yeasts want the sugars in barley, hops, and grape juice, so of course they will multiply and ferment that sugar until it's all alcohol. Some breweries have their own, unique strains of yeast, just so that you know at least one thing is different from one bottle of wine to the next.
If beer and bread are not enough of a reason to like yeast, dried yeast (the same kind) is used in vegan cheese substitutes. It is high in protein and emulates the flavor pretty well. Go figure; a fungus tastes like rotten milk.
This looks like an acid-tripped slice of fruitcake.
Of course, there are many kinds of yeasts, and not all of them are helpful. Cryptococcus neoformans and any yeast from the genus Candida are all known to cause yeast infections. Many yeasts dwell in the moist environment created by mucus membranes, only becoming infectious if the immune system is compromised. Candida infections are the most common, and rarely fatal. Cryptococcus is one of the defining infections for AIDS. Even if they are only present in those with weakened immune systems, yeast can still be a threat.
It's just so tasty that we usually don't care.