Dear Mr. Wizard:

In the November '97 issue of BYO, Jim McHenry asked Mr. Wizard about low yields from his mash. Jim suspected poor mash-temperature control was the culprit. He was using what sounded like a standard homebrewer's thermometer. I eagerly read Mr. Wizard's answer because I had a similar problem using similar equipment five years ago when I went all-grain. It pains me to say it, oh Master of Mash, but you let Jim and me down. Although you were absolutely right with the information you gave Jim, you didn't really answer his question. I had trouble with temperature control, too. Experience taught me that patience is indeed a virtue when mashing. I give my thermometer 10 minutes before I decide to read it. If Jim is using a pot for a mash tun that he heats on the stove, my advice is to heat his mash water to 165° F, put the lid on, and take the pot off the stove. Wait a few minutes (five is good, 10 is better with a slow thermometer) and take a reading. If the temperature is still 165° to 167° F, you can mash in with room-temperature grist. My average temperature drop at mash-in with 100-plus mashes is 10° to 15° F. This puts me firmly in the 150° to 155° F bracket for my mash. You have to trust me on this one, Jim; it really works. Stir just enough to ensure no dry spots and don't look at your thermometer for 10 minutes. Leave the lid on and wrap the pot in a blanket to keep it cozy. This will probably take care of Jim's temperature anxiety. I hope this information helps and that I haven't offended the Emir of Enzyme.

Tom Bechard
Rouses Point, N.Y.

Mr. Wizard replies:

Thank you for the added information. Your advice to remove the mash pot from the stove is sound because a hot burner will continue to heat the mash long after the heat is shut off.

This would certainly explain a mash that is hotter than expected. A problem I have encountered with thermometers but failed to include in my original answer to this question is calibration. Some thermometers, especially dial thermometers, can be significantly out of calibration. The best way to check a thermometer is to measure the temperature of melting ice and boiling water. These temperatures should be 32° F or 0° C and 212° F or 100° C, respectively.

Because the boiling point of water is dependent on atmospheric pressure, high- and low-pressure weather systems will cause slight fluctuations in the boiling point. In any case, I have encountered many out-of-calibration thermometers that were the source of error, especially wort-fermentability problems, from seemingly normal mashes.

Dear Mr. Wizard:

I have one soda keg that has produced three batches in a row of different beer recipes with an iodine or other strong chemical taste. My other keg has never had a bad batch. The beer smelled fine prior to kegging. Is iodine or strong chemical taste a common off-flavor for beer? Is it something in the keg?

T. Shelburne
Madison, Wis.

Mr. Wizard replies:

Chemical off-flavors are frequently encountered in beer and can be caused by numerous factors. The most obvious cause comes from traces of cleaning or sanitizing chemicals left on equipment surfaces after use. Chemicals containing chlorine and iodine are well known contributors of chemical off-flavors if the compounds remain on the equipment. Of the two, chlorine is the worst because it can combine with malt phenols to form a class of compounds called chlorophenols, which have a pronounced medicinal aroma. Iodine sanitizers usually cause no problems if used at their recommended concentration.

Some brewers encounter problems with chlorine even without using chlorinated sanitizers. These problems are often traced to chlorinated tap water. If brewers use chlorinated tap water for rinsing brewing equipment, then chlorophenol off-flavors may arise. One well known craft brewer had a problem with chlorophenols in his fruit beer that was eventually traced to the fruit. The fruit source had been rinsed at the farm with chlorinated water and this chlorine was being introduced to the beer at the time of fruit addition. This problem took some good detective work to solve.

Medicinal aromas can also come from wild yeast contamination. In fact the classic indicator of wild yeast contamination in beer is a distinct phenolic aroma. This aroma is often likened to cloves or the smell of standard bandages.

These are all possible explanations to your problem, but I don't think they are the real culprit. All of your beers from all kegs would taste off if it were due to your chemical selection or city water, and wild yeast attacks probably would not be limited to one keg, although that is certainly possible.

I think the most probable cause of the off-flavor is leftover flavors in the keg gaskets. I think you have an old root beer keg on your hands, and the aroma in beer is not iodine or medicinal but root beer. The most notable aromas in root beer are phenolic by nature and do smell somewhat medicinal. They are also next to impossible to completely remove from rubber gaskets they contact. Many a pub brewer will tell awful stories of contaminating beer lines, gaskets, hoses, and beer fillers with root beer where the only solution was to replace all soft parts. This can be expensive in a commercial brewery! The lesson for them is to keep their root beer away from everything else. In your case you inherited the taint, but the solution is the same.

Take your suspect keg apart and remove all rubber O-rings and gaskets and replace them. Most homebrew stores selling kegs and kegging equipment will carry or have the ability to order replacement parts. Even if the problem is not from root beer, your problem is most likely associated with the keg's previous resident!

Mr. Wizard, BYO's resident expert, is a leading authority in homebrewing whose identity, like the identity of all superheroes, must be kept confidential.

Do you have a question for Mr. Wizard? Send him an e-mail at This email address is being protected from spambots. You need JavaScript enabled to view it. .