Stout question

I've read that lots of people on here let their imperial stouts sit up to a year before consuming. My question is when the commercial brewers make a stout does it really take them that long? Any idea on average how long they ferment them? Thanks

They don't choose how long the ferment takes, the yeast do. You are talking about aging/conditioning. I'm not 100% sure how long it takes for the commercial brewers since they have state of the art equipment at their disposal, but in general, the bigger the beer the longer it has to age for the flavor to improve...

It depends on the brewery and their procedures. If they pasteurize it seems it would be a waste of time to age them this long, since there is nothing living working in the beer. Bottle and cask conditioned beers are still alive. Also it depends on their goal--are they shooting for as short of a pipeline from mash to consumer as possible or are they shooting for the perfect example of the style? If they want short quick turn-around then they want something that is representative of the style and will appeal to the drinker. If they want to make the "perfect" RIS then they will age longer. I buy some commercial beers that are aged far more than a year. I find others of the same style that have little if any age on them. Also, the big guys have full blown labs on their side to find ways to get the taste from the ingredients and techniques available to them. As homebrewers we don't have this, so we have to use what works simpler.

I understand that the fermentation length is determined by the yeast activity, just didn't know how long they let it sit after the fermentation was complete.

Each place is different, and each beer as well.