M.D.L MetaBeer

According to the fermentation model, beer types roughly consist of the following types.
Top Fermenting Beers
When you say beer is top-fermenting, it means that the yeast used in the fermentation process settles at the top of the liquid. The yeast has a higher alcohol tolerance and will ferment at warmer temperatures. Some examples of top-fermenting beers are IPAs, stouts, and wheat beers
Bottom Fermenting Beers
Lager yeast is much more fragile than ale yeast, which means that the yeast strain would settle at the bottom of the vessel after fermentation. Unlike top-fermenting beers, the yeast in bottom-fermenting beers ferment more slowly and at cooler temperatures. It also has a lower tolerance to alcohol. Some examples of bottom-fermenting beers are Pilsners, Bocks, and Oktoberfests.
Spontaneous Fermentation Beers
This fermentation process occurs when brewers pour the wort (unfermented beer) into a vessel and then leave the vessel alone. The beer then picks up natural fauna in the air.*
* References