Dear Mr. Wizard,

How do you reduce the amount of phenolics in a beer? My recent beers have had a slight distaste of cloves, which I´m not too fond of. Is the presence of phenolics due to the yeast strain or what? One final question — if you are reusing the yeast for another beer, should you take it from the first or second fermenter?

Richard Heidemann
Alleroed, Denmark

Mr. Wizard responds:

You are correct that a yeast strain is the most common cause of phenolic aromas in beer. The classic clovey, phenolic producing yeasts are those used for German-style hefeweizens. These yeasts convert ferrulic acid from malt into the unmistakable 4-vinyl guaiacol, which smells just like cloves. As it turns out, wheat malt contains more ferrulic acid than barley malt and if you actually wanted to try to produce more clove flavor using the same yeast strain, using more wheat malt is one way to do that. This is just the opposite of your goals.

Weizen yeast is not the only type to produce detectable concentrations of this compound. Many of the Belgian strains produce enough phenols to leave a not-so-subtle fingerprint in the finished beer and some British ale yeast produce barely enough to be detectable. The other types of yeast that are known for the production of phenols are wild yeast strains. In general, a wild strain is any strain growing in your fermenter other than the one intended. The phenolic aroma from wild strains is usually not the pleasant clove found in weizen beer but is more of a strong medicinal aroma similar to those wonderful phenol sprays like chloraseptic that dull the pain of a sore throat.

Medicinal aromas can also come from the reaction of chlorine with phenols produced during fermentation. The dreaded chlorophenol off flavor arises when chlorine, usually from bleach sanitizers or heavily chlorinated water, and fermenting beer commingle. One precaution to take if you suspect this to be the problem is to eliminate chlorine from coming into contact with beer. That can be done simply by making the decision to not use bleach as a sanitizer or being sure to rinse thoroughly after use. Also, be sure to use brewing water that is chlorine-free. One method used to remove chlorine from water is to add potassium metabisulfite (found in Campden tablets).

These days there are plenty of good brewing yeasts on the market and if you are pitching yeast from a well-known supplier, I doubt the yeast is contaminated with wild yeast. In the late 1980s and early 90s that was not uncommon, especially in some dried yeast, and phenolic aromas were often blamed on the yeast supplier. Today, if the phenolic aroma comes from the yeast it is probably a purposeful trait for the strain. So, switching strains may help alleviate your problem.

We always harvest and re-use our yeast (like other commercial brewers) and the accepted rule is that yeast should be cropped as soon as possible when its viability and vitality are at their peak. Some ale brewers continue to crop yeast from the tops of an open fermenter and this is done towards the end of peak fermentation before the cap begins to fall into the beer . . . although in the case of some top fermenting strains the thick kraüsen never really falls.

Most brewers these days harvest yeast from the bottom of conical fermenters and one must wait until the yeast is on the bottom and can be taken. Our ale flocculates pretty well and we can harvest yeast about 3–4 days after primary fermentation is complete. The longer you wait to harvest and reuse your yeast, the greater the chance of having sluggish, not-so-healthy yeast in your next batch. I would suggest not reusing yeast that has been sitting on the bottom of a carboy for any longer than two weeks.

Dear Mr. Wizard,

I brew a pretty good nut brown but I would like to increase the distinct nutty flavor. I’m not sure what ingredients or combination of ingredients produce this flavor. Could you help me out?

Rebel Tjomsland
via email

Mr. Wizard replies:

I guess it really depends on the type of nut brown ale you are brewing. I mean if it is a pea-nut brown ale I would reach for more peanuts and if it is a hazel-nut brown ale I would add more hazel nuts. Sorry, but I couldn’t resist the obvious!

The nutty flavors found in brown ales and other dark beers come from malt. And nutty flavors in malt are formed during kilning when reducing sugars react (glucose and maltose, for example) with amino acids and polypeptides in the frequently cited Maillard reaction, named after the French chemist Louis Camille Maillard who discovered the reaction in 1912. Although pale malts do contain Maillard reaction products (MRPs), it is the group of MRPs that undergo Strecker degradation, a reaction where intermediates in the Maillard reaction combine with amino acids and condense into nitrogen-containing cyclic molecules. These molecules have biscuity, nutty and toasty aromas. Adolph Strecker (1822–1871), by the way, was a German chemist born in Darmstadt who developed a method to synthesize amino acids and identified the so-called Strecker degradation in the laboratory before the Maillard reaction was discovered.

The products of the Maillard reaction and Strecker degradation range from toasty to burnt — in the middle is nutty. Maltsters can adjust kiln temperature and moisture content during kilning and roast malts with varying degrees of modification to influence the flavors of roasted malts and ultimately beer flavor. One of my favorite brews is a brown ale that my brewery makes once every year or so that contains brown malt. The signature flavor from the brown malt is a dry, roasty nuttiness that I really like.

Other malts that give the type of flavor you seek include Munich malts, especially darker types, biscuit malt, aromatic malt, amber malt and other high-kilned malts. One of the best ways to select malt for a brew is to taste it or, as many brewers say, “chew” the malt. Munching on malt is a great way to evaluate its character as it gives a good idea of hardness or friability (ease of milling), can sometimes indicate evenness of modification and gives a straight-up sensory profile of that one malt. Sometimes when I am searching for a flavor I can’t adequately describe with words I find what I am after when chewing on malt samples.