Dear Mr. Wizard:
I am a first-time homebrewer and am concerned about my primary fermentation temperature. The maker of the brew kit says to cool the wort to 70° F, then pitch the yeast into the wort in my primary fermenter. I have pitched the yeast into the fermenter but I cannot keep the temperature at 70° F. The lowest I can keep a stable temperature is between 74° to 80° F by wrapping the fermenter with wet towels and keeping a fan blowing on it. The air lock is bubbling nicely and the wort had a starting specific gravity of 1.044, which is right on the mark for the recipe. Will this higher temperature ruin my brew?
Litchfield Park, Arizona
Mr. Wizard replies:
Congratulations on your first brew! If you followed the directions on the kit and only departed from them by using a higher fermentation temperature, your beer should turn out fine. I am assuming you cleaned and sanitized everything properly, used a high-quality kit and fresh yeast. High fermentation temperature alone won’t ruin a beer.
Temperature does play a crucial role in flavors generated from yeast during fermentation. As temperature increases, fermentation rate accelerates and with this faster fermentation come more aromatic compounds. The aromas arise because the metabolic rate is going along at such a clip that more metabolic intermediates are excreted from the yeast cell. I liken this to people getting stinky and sweaty during vigorous exercise.
“Fruity” is the most common type of aroma associated with warmer fermentations. This generic term includes aromas reminiscent of banana, pineapple and pear, which belong to a class of compounds called esters. Some esters, like ethyl acetate, smell like solvent (ethyl acetate is used in acetone-free fingernail polish remover). I don’t mind fruity beers but I hate smelling fingernail polish remover when trying to enjoy a pint.
Warm fermentation also increases the alcohol concentration. High alcohol levels are known for their spicy, vinous aroma and the propensity to cause headaches. Strong beers normally have detectable levels of higher alcohols but normal gravity beers, like the one you brewed, shouldn’t have a detectable level.
If you discover after bottling and aging that your beer smells fruity, solventy and vinous, the warmer fermentation is probably the culprit. You may want to investigate other methods of keeping the fermentation cool. Since you live in the hot, metropolitan area of Phoenix, you probably can’t restrict your brewing to the “cooler months” of the year. If you like the hobby and have some extra space in your house, try a used refrigerator. You can buy a temperature controller through various homebrew suppliers that overrides the built-in thermostat and allows you to set the refrigerator to maintain warmer temperatures.
Dear Mr. Wizard:
I brewed a batch of oatmeal stout the other day and one day later, I observed a good, vigorous fermentation. However, after this one day of active fermentation, the activity dramatically slowed (to approximately one bubble every 30 seconds). I am hoping you can tell me how I can un-stick my stuck fermentation?
Mr. Wizard replies:
The most common cause of a fermentation that takes off, then quickly slows, is poor wort aeration and/or underpitching. What you have described is actually not consistent with the term “stuck fermentation.” A stuck fermentation ferments for several days but the final gravity gets “stuck” at a higher level than the true final gravity of the wort. The only way to properly diagnose a stuck fermentation is to run a forced fermentation, during which the wort is over-pitched and fermented warm. At the end of the forced fermentation you can measure the final gravity and use this number as a benchmark. Though it is effective, this is not a practical method for the homebrewer.
Stuck fermentations are frequently caused by yeast that prematurely flocculate. In most cases, the yeast have been overused and are beginning to lose some of their basic properties. Another possible cause could be nutrient deficiency in the wort (especially low levels of zinc).
Some brewers will try to rouse a stuck fermentation by racking it, or they may kraeusen the beer to try to get it to the proper final gravity. Kraeusening involves adding a small amount of new fermenting wort to a fully fermented lagering wort with the intention of creating a secondary fermentation.
In your case, I am willing to bet that you underpitched. Though you observed bubbling in the first day, this early activity can occur even if you underpitch as long as the yeast carried with it some glycogen or intracellular food. When yeast go dormant, intracellular levels of glycogen increase and this energy reserve is used to get the yeast cell going when the dormant stage is relieved. In a brewery, dormancy is relieved when a stored liquid yeast culture is warmed and tossed into aerated wort.
The other scenario is when dried yeast is re-hydrated and tossed into aerated wort. In either case, yeast will use the glycogen as a source of glucose and all of the telltale signs of fermentation will be observed.
After the yeast uses its glycogen reserve, it will then use the nutrients in the wort to continue fermenting. This is where aeration comes into play. If the wort is poorly aerated, cell growth will be restricted and you can have a very long “lag” phase, during which the population of yeast remains flat and the fermentation rate is very slow.
The fermentation rate begins to increase as the yeast cells kick into their growth phase. At some point, yeast cell growth subsides and the fermentation rate begins to trail off. If everything went right, this point should coincide with the final gravity of the beer.
I have beaten the concept of adequate pitching rate to death in the past and I’m sure that many readers of this column are tired of hearing it. I also have harped on aeration, but not quite as aggressively. I have forgotten to aerate brews in the brewery where I work and the results have been astounding — as in “what the heck have I done?” astounding.
Worts can be aerated once fermentation begins and this technique will impact beer flavor. The traditional “Yorkshire Stone Square” method of fermentation constantly recirculates the fermenting wort through a glorified shower head. This method of rousing was apparently developed to deal with brewing yeast that are very flocculent and demand lots of oxygen. Unless you are equipped to do this, the best advice is to let fermentation slog along until it finishes. You could also pitch more yeast or kraeusen with an actively fermenting half-gallon of wort.
My diagnosis may be totally wrong, but the best thing is to learn from this experience and try to avoid repeating this mistake. If you do not currently have some sort of aeration device, such as an aquarium pump, get one. Shaking the carboy is no substitute for an aeration device that actively carries air or oxygen into wort.
If you think that you underpitched, review your pitching methods. A rule of thumb is: one cup of thick yeast harvested from a fermenter or one quart propagation per every five gallons of wort. If you simply follow this advice your future fermentations should, almost always, go off without a hitch.
For more of Mr. Wizard’s wisdom, please see the the latest issue of Brew Your Own now available at better homebrew shops and newsstands.