So what to the pros do? Why does, say, a Sam Adams taste exactly the same year after year? (Not attempting to criticize. Just really curious).
Lot's of lab work and planning (way beyond the scope of a humble homebrewer). And it doesn't taste exactly the same, but it's darn close (closer than I'll ever get two batches). Most have a staff of tasters with a goal of getting it as close as possible. I once read an article on what Bud does, and it is amazing the differences between the different regional brewers same version of the same beer.