Hop Brand Matters
So a while back I was brewing with one of my favourite hops, East Kent Goldings. In theory, you're not able to call a hop East Kent Goldings unless it actually comes from East Kent, though based on what happened, I doubt I'd be able to determine that with any sense of certainty. Anyway.
It's well know that hops tend to age terribly, with the exception of Noble hops where they age "gracefully". You won't get the same AA%, but you'll get a reasonably pleasant floral aroma out of them. East Kent Golding is not a noble hop. Old EKG imparts an almost astringently harsh bitterness to it. I had bought a pound of it and made an imperial stout with it where the harsh bitterness didn't matter and so I didn't notice. I then made an English Mild. Boy, did it matter there. At this point, I thought that the mild was just a bit too dry and I decided to recalibrate my thermometer and double check the mash temperatures. I brewed an English Bitter and that harsh, drying sensation was still there. I checked the water. I took apart valves. I scrubbed and scoured every inch of equipment I owned. A Scottish Ale later with the same harsh, biting bitterness at the end made me check my ingredients. That harshness only showed up when I used those hops.
So I checked the hops. There was no "cheesiness" to them, which is usually the go-to marker for old hops, but not all hops age the same way. I checked for a date. There was none, but there was a batch number. I decided to look up the company and see if I could get more info.
Suffice to say that the company was a subsidiary of a subsidiary and I got no further with my search. Apparently the batch number was for internal use only. I decided to look up a few other trusted hop companies to see what they were selling as EKG and the youngest you could buy at the time was two years old.
So I got real picky about hops and here's some advice for buying your own:
The company selling them matters
There are a lot of brand new hop growers out there. That doesn't necessarily mean that they're poor quality, but it does mean you should ask some questions. What's their drying process like? The best hop drying kilns should have 3-4 layers. Cheaper kilns have a single layer and the hops are turned to even out the moisture. Hops on the bottom can end up burned and hops on the top can end up with mold. What's the harvesting process like? There have been more than a few reports of non-hop material making it into the pelletizer. Remember that hops, especially with modern dry hopping techniques, should be treated as a food product. On the commercial side of things, this wasn't always the case simply because hops were always boiled. It was also the case that AB InBev, due to market dominance, was able to demand all hop growers adhere to certain standards. Newer hop yards growing newer varieties haven't always had the necessary input from breweries until the Hop Quality Group. Unfortunately, as of this writing, there isn't a certification process to ensure that they adhere to HQG's standards so the brewer will have to do their own legwork.
Growing region matters less than quality
I've said before that you can't brew X style without X ingredient, or that hops display terroir. That's still true, but when it becomes impossible to get a quality hop from the region you want vs a substitute grown locally, always choose the substitute grown locally, assuming you trust the grower. For my example above with the EKG, I couldn't get any that was less than two years old. Instead, I had to go with BC Golding that was harvested a mere 6 months ago. I also had the choice of Willamette harvested at the same time - both are perfectly acceptable substitutes and even though they aren't exactly what I was looking for, they were far better than a 2+ year old hop for the sake of authenticity. These are choices that commercial brewers also have to make. In fact, sometimes buying in commercial quantities means you actually have less access to coveted hop varietals than buying in smaller quantities.
Most drinkers/judges won't be able to tell what hop you used, but they will be able to tell if it's off.
For all the talk about terroir and hop flavour, unless you're brewing an intensely dry hopped beer (and even then, for maybe a couple weeks), you're only going to get a few generic adjectives worth of aroma out of your beer. If I put an English Pale Ale dry hopped with EKG and one dry hopped with Willamette, some drinkers would be able to tell there was a difference, but few would be able to tell which was which. On paper, they sound like very different hops. In practice though, as long as it has "English" character, it will pass muster.
However, if you use an old hop, particularly one that doesn't age well (which is most of them) you will get some very unwanted compounds. Old EKG has a harsh bitterness. Old Fuggles has a sulfitic bite to it. Old El Dorado tastes like tobacco. A lot of the newer "fruity" hops taste like onions once they have a bit of age. It isn't pleasant, so don't feel bad if you have to substitute. You'll feel worse when you have to down a keg that tastes like ranch dressing.