I looked it up. Michigan has 3 distinctions and it affects where you can sell your beer.
Over 60,000 barrels, you are a brewery and can only sell beer at a maximum of two brewery locations (and of course to licensed retailers).
Under 60,000 is called a microbrewery but still has two separate distinctions:
30,000 - 60,000 barrels you can sell at 3 locations.
< 30,000 you can sell at any amount of brewery locations.
Brew pubs have a special distinction, they must be under 18,000 barrels, cannot sell to retailers, and 25% of their gross sales must be from food or non alcoholic beverages. So the breweries by my house are those, you can only get their beer at their locations and both sell food.
The taxes differ too but it seems to be brackets so everyone pays a lower tax on the first 60,000 barrels, then it's higher beyond that.