Keep in mind, this question is coming from a newby…
So I always heard, “the longer your beer sits, the better it is going to taste.” Well, I have seen [er, tasted] the promise land. As I got towards the end of my Irish Red batch, it really did taste better; the extra 31 days to sit made a huge difference. So my question is, what are the pros and cons of letting a beer sit 31 days longer in a secondary fermenter or in bottles? Would I have got the same taste of my Irish Red with another 31 days in a glass carboy?
You’ll probably get some differences of opinion here. Some like bulk conditioning, others aren’t so sure. The one thing that could eventually make a difference is the time the beer spends on the spent yeast and hops. I don’t know how long the beer was in the fermenter originally, but the addition of another four plus weeks may be a little too much time on the trub. If you had already racked to secondary, then you’re good with the additional time. I think if fermentation was complete, you would be better off to simply bottle for conditioning rather than risk oxidation or infection through racking to secondary for conditioning. Some of the bigger beers do really nicely with extended bulk conditioning, but these are usually in a secondary vessel. As noted, you will probably get some differences of opinions here. You will eventually want to try it and see what your results are.
Different types of beer have different requirements, and will evolve differently with time. And as personal tastes vary, you will get different opinions. But I think most will agree that you can leave pretty much any beer in the primary for at least 3-4 weeks without any risk. At some point after that, most beers should be bottled or moved to a secondary, because there is at least a theoretical risk that the trub could generate off flavors over time, and the protective layer of CO2 that blankets the beer will disperse leaving it vulnerable to oxidation. But there are exceptions. On Saturday I racked a lambic out of the primary - 18 months after I put it in there. There is no doubt that the 1.5 years in primary help to develop the funky flavors I was looking for, but I doubt you want that in most of your beers.
In general, leaving the beer sitting in bulk has two big benefits: it results in clearer beer (doesn’t matter if it sits in primary or secondary, it will clear either way) and it will keep you from drinking it too early. Some beers - especially very malty or high alcohol beers - benefit greatly from aging and allowing the flavors to meld and mellow. Others are better young, such as hoppy beers. But I find that I prefer even my hoppy beers to be aged at least a month or more to cut the green flavors.