[_ak]

Regarding 3: the same goes for beer, except you can mess up over the course of just a few minutes to an hour instead of a few months. Crush your malt too fine or too coarse, mess up the mash temperatures, and you end with things like a too high or low efficiency, a stuck sparge, or too many fermentable and unfermentable sugars. Of course, in a fully automated industrial brewery this usually isn't a problem, but your typical nano or micro-brewery is a still a lot of manual works, and thus many ways to mess up manually.

Edit: and now that I think about the other things:

Regarding 1 and 2: some hop varities have mildew problems, and bad weather has negative influence on the growth and other things like alpha acid, so bad weather can have quite the impact on hop quality and availability. The 2013 hop harvest in Germany was quite the disaster, apparently. AA% is a lot lower, and young plants of some new breeds got way too much water.

[poulsbohemian]

All great points, thanks for the info!