Chemistry of the Wet Hop

[I'm out of town until September 18 and away from computers of all sorts. On the assumption that you won't have read every post from the past 3 years, I'm reposting a few favorites. See you soon.]

In my earlier post, I discussed hops generally. But what about wet hops and dry hops? To my palate, they're radically different. Last year, as I was systematically working my way through fresh-hop beers, I discovered that they perform so differently that it's clear brewers are still figuring it out, too. (That's one of the main reasons I'm trying to exhaustively document what I've tried--so that I can get a handle one which fresh hops seem to taste the best.) So the question I'd like answered is this: what happens to the chemical compounds when a hop is dried? Of to put it in the reverse, when a hop is wet, what are the volatile compounds we're tasting that are normally absent or just minor notes in dry hops?

Okay, it remains elusive. I'm no chemist, just a simple blogger. But there is some science to suggest that when an herb dries, its chemistry changes. In the paper quoted below, scientists looked at various compounds present in freshly-harvested herbs and the same herbs after they had been dried.

The herbs of lemon balm, oregano, and peppermint were analysed immediately after harvest and after drying to determine their antioxidant activity and content of total phenolics, l-ascorbic acid, and carotenoids. The strongest inhibition of linoleic acid (LA) peroxidation was found for fresh and dried oregano. For peppermint and lemon balm it was significantly lower and decreased after drying. The ability to scavenge the free radical DPPH (2,2-diphenyl-1-picrylhydrazyl) was very high in almost all tested samples, exceeding 90%. The three species tested had a very high content of total phenolics and drying of oregano and peppermint resulted in their considerable increase. The highest content of ascorbic acid was determined in fresh peppermint and lemon balm and carotenoid content was at a similar level in all the species tested. Drying caused great losses of these compounds.

You can follow the link for the technical discussion. But to highlight just how radically things change, just 6-15% of the vitamin C is present in dry forms of these herbs. The hop cone contains oils, acids, co-humulone, and other components. If one of those is ten times as robust in wet hops as dry, it would begin to explain why the beers taste so different.

Quick, someone take a hop into the lab and get on this.

Originally posted September 30, 2008