Matt Malloy will never forget the first time he had to throw out a batch of beer. The recipe, a barleywine aged in Barbados Rum barrels, picked up musty notes of decomposing wood that didn’t compliment the base beer, he said. While dumping beers is often a necessity for brewers who dabble in barrel-aging, it hardly ever gets easier. “It definitely is hard watching all that time, effort, and cost, just go out the window,” said Malloy, head brewer at Denver’s River North Brewery.