Craft beer off-flavor diagnosis: Eastside Brewers Collective breaks it down

Sometimes you can learn a lot by figuring out what you DON’T like. This was the idea behind an “off-flavor” beer tasting led by Jeff Koehler, Ph.D., a chemical engineer and home brewer with the Eastside Brewers collective.

The tasting was held at the Eagle Rock Brewery. Owner/Brewer Jeremy Raub was there, along with his partner and brewery blogger,Ting, to help with the tasting and serve up delicious Eagle Rock brews on tap afterwards. The VCBE tasted Stimulus, a Belgian Amber made with Intelligentsia Coffee. The VCBE will be interviewing Raub in a future column.

Koehler, whose day job is Principal Scientist for Nano H2O (“Next Generation Water Purification Technology”), offered a selection of eight beer tastes whose flavors were not quite right. He added a small amount of “secret chemical ingredient” to cups of Coors and invited the participants to call out the smells and tastes they experienced.

To give us hints, Koehler provided copies of the American Homebrewers Association “Beer Fault List” along with two “beer flavor wheels” and handouts for each of the off-flavors. Here’s what we learned:

1. "Smells like green apples" - Acetaldehyde. Present in all  beers, off-flavor at high concentrations – a problem with the yeast

2. "Kind of a buttery, lardy, greasy flavor" - Diacetyl. Again, a problem with yeast/fermentation

3. "Canned vegetable smell, kind of like creamed corn" - Dimethyl Sulfide (DMS). Desirable in some pale lagers, off-flavor in most beer. Usually a sign of too much pilsner malt or a weak yeast starter

4. “Old socks;” sweaty, stale cheese - Isovaleric. Classic “old hops” flavor

5. Floral, almost like rose petals or rose water- Geraniol. Partly the floral component of hops, particularly Saaz, characteristic of Bohemian-style pilsners. Off-flavor comes from too much hop oil late in the boil

6. “Baby diapers.” Several people made the observation that a certain popular beer bar in Pasadena regularly gets this chemical component in the beer they serve - Butyric. Formed by bacteria, and usually indicative of “line issues” – old lines, or ones badly in need of a cleaning

7. “99 Cent Store” smell: a kind of plastic-y, mothball, musty odor- Indole. Often present with DMS, formed by contaminant “coliform” bacteria. Small amounts are present in normal beer due to thermal breakdown of tryptophan…

8. Pickles or vinegar - Acetic. Present in all beers, responsible for the “sour note” in certain Belgian-style beers.