Are hops fermentable by beer yeast? Do they contribute in any way to the resulting ABV?
Interestingly, I found a presentation by Thomas H. Shellhammer, professor of fermentation science at OSU, that shows the composition of a typical hop cone:
- Cellulose and Lignin: 40-50%
- Protein: 15%
- Alpha Acids: 2-15%
- Beta Acids: 2-10%
- Water: 8-12%
- Minerals: 8%
- Polyphenols and Tannins: 3-6%
- Lipids and Fatty Acids: 1-5%
- Hop Oil: 0.5-3%
- Monosaccharides: 2%
- Pectin: 2%
As you can see, there are trace amounts of monosaccharides (e.g., fermentable sugar) in hops, but since you're adding such a small amount of hops (say, 2 ounces per 7 gallons of water for a 5 gallon batch), any sugar you get from the hops is absolutely miniscule.
So, while theoretically hops might contribute some fermentable sugars, they would be in such a tiny amount that I doubt the yeast would have anything extra to feast on, and there would be no affect on the beer's final ABV.
While hops may have a very small amount of sugars in them, it's not enough to make any discernible difference in your beer. However, they do appear to have diastatic power which could slightly affect your ABV. That's a lot of maybes, though. There was a discussion of that in Episdoe 12 (Going Stale) of the Experimental Brewing podcast based on this paper: THE DIASTATIC ACTIVITY OF HOPS, TOGETHER WITH A NOTE ON MALTASE IN HOPS.
Not that I'm aware of. At the very least, in my experience hops are never taken into account as a fermentable sugar contribution so if there is some small amount of sugar present in the hops, it would be negligible enough that no one ever cares to mention it. And at the levels some people dry-hop I'd imagine we would have started noticing it by now.
Plus, hops are used in beer to create bitterness and flavor compounds that balance and complement the sweetness created by the malt sugars. So if they were adding a noticeable level of sugar they'd be working against what is basically the primary reason they're used in beer in the first place.