Yeast Problems, Fermentation Temperature & Oxidation: Mr. Wizard


I’m an extract brewer (that also steeps) and I recently noticed a bunch of white spots on top of my brew (which was a wheat recipe) after I transferred it to the secondary. I thought it was mold forming but read that it’s probably “yeast rafts” or flocculated yeast clumps. The beer turned out nicely but I’m curious at what causes this to happen? Are certain beer styles more susceptible to this phenomenon?
Andreas Bettin
Toronto, Ontario

I am not completely sure about the nature of these little floaters. I think, however, that it is possibly either yeast, as you suggest, or protein clumps. Some yeast strains have a tendency to form a dense top crop. When these beers are racked some of the top cropping yeast is carried over and the appearance is at times strange. Weizen yeast is an example of an aggressive top-cropper. In the case of Brettanomyces, a pellicle is formed on the surface of the beer and also has an odd appearance.
This could very well be the early signs of a Brettanomyces pellicle forming on the surface of your beer. If this is the case it is an indication of a problem, unless you intentionally added this yeast type.

Brettanomyces is one of those strains considered to be “wild” and can be a problem to control if you bring it into your brewery and do not have rigorous sanitation procedures.

The other thing that may be responsible for the unusual appearance in the fermenter is trub carry-over from the brewhouse. Wheat contains a significant amount of gluten proteins and when wheat malt is mashed the glutens tend to be retained in the mash and discarded with the spent grain. If you steeped some wheat malt it is possible that some of these gluten proteins made it into the fermenter and resulted in the odd appearance.

The good news about things like trub and yeast that collect on the top of fermenting beer is that you can rack the beer away from the solids and there is no detrimental effect on beer quality. If this beer begins to start smelling leathery, earthy and like a barnyard after a few months of storage the source was likely Brettanomyces. If that proves to be the case you should be careful handling the bottles since Brettanomyces is a super-attenuating strain that will slowly ferment dextrins in your beer that Saccharomyces species cannot. This can result in bottle grenades.


For those of us without temperature controls through fermentation, has anyone done any experiments with changes in wort temperatures? It would be great to hold 65 to 68 °F (18 to 20 °C), but what about a 70 °F (21 °C) start, dipping into the 60s (~18 °C) then allowing the temperature to increase back into the 70s (~20s °C)? Or, starting in the 60s (18 to 20 °C) and creeping up into the mid 70s (23 to 24 °C)? Is there any way to predict the yeast flavors when the temperature is moving?
Michael Florez
Via Facebook

The batch size for most homebrewers has been around 5 gallons (19 L) for a very long time, and keeping this volume of fermenting beer cool is not difficult. Recently, however, many homebrewers have become interested in controlling fermentation and aging temperature and all types of fancy rigs are being built to make little fermentation cellars for use at home. To boot, batch sizes for many homebrewers has increased and the heat of fermentation is more difficult to remove in these larger vessels.

The short answer to your question is yes; there is a long history of fermenter temperatures moving up and down during fermentation. At one time it was common for tanks to be equipped with attemperation coils, or pipes inserted into fermenters for the purpose of temperature control. A fairly common method used for attemperature coil operation is to monitor the fermenter temperature with a thermometer and to simply turn the cooling valve on for enough time to cool the fermenter and then after some time the valve is turned off. This method of tank control is called “on/off” control and is how most thermostatic controls are operated. Since manually controlling fermenters with attemperation coils requires brewers to manually monitor and control fermenters the result is a temperature profile that moves up and down around the desired temperature.

Predicting how temperature affects flavor is not an exact science, but in general terms the effects of fermentation temperature on beer flavor are well known. Beer flavor is cleanest when the fermentation temperature is as low as possible for a given yeast strain without causing problems with sluggish and/or incomplete fermentations. As temperature increases the production of esters increases and fruity aromas increase, especially for beers made with strains that are noted for the production of aromatics. The production of these compounds is greatest at the peak of fermentation and it follows that the most critical point to consider for temperature control is this peak in activity.

Commercial brewers often begin fermentations cooler, usually about 5 °F (3 °C) cooler, than the controlled temperature, which you can try. One reason for allowing the fermentation to experience this “free rise” is that tank temperature is easier to control when the fermenter is being mixed by the activity of fermentation. After fermentation is complete the temperature is lowered. If you plot temperature over time the result is a curve that goes up and down.

To summarize, temperature fluctuations are normal and the most important temperature to control is the peak temperature experienced during peak activity. Also, starting cool and allowing your fermenter to warm up is a good method to consider if you lack refrigerated cooling. To keep the peak from getting too high you can use a low tech method such as plunging your carboy into an ice bath for 20 minutes or so at a time, a method that mimics turning on the valve of an attemperation coil.



I am brewing beer to fill a 13-gallon (49-L) oak barrel. When I fill the barrel I am going to pitch a smack pack of Wyeast Roeselare and a White Labs Belgian Sour Ale I vial. I am brewing two 5-gallon (19-L) batches that are higher in gravity than desired in the barrel and going to dilute it with boiled and cooled water to top off the barrel. My question is will the yeast that I am pitching metabolize the oxygen that is still dissolved in the water during the aerobic growth phase or is it destined to be oxidized.
Ronald McGuire
via email

You are absolutely correct that adding water to the fermenter as the fermenter is filled, or even to the wort following boiling, is not a problem because the yeast will indeed metabolize the oxygen in the early stages of fermentation.

I am a bit confused by your method, however. It seems that you are planning to pitch a mixed culture of yeast and bacteria into your wort and conduct your primary fermentation in the barrel. While there is nothing wrong with this approach, you will experience excessive foaming and beer loss if you top the barrel up before the primary fermentation begins.

An alternate approach that may work best is to adjust your batch size so that you end up with a total of about 14 gallons (53 L) of wort after you have added the dilution water. If you typically ferment in 5 gallon (19 L) carboys you will want to split the batch into three carboys and conduct the primary fermentation. After the peak activity has slowed down in about seven days you can then rack
the beer into the barrel. The advantage to this method is that you will be able to completely fill the barrel without worrying about a big mess due to over-foaming during the primary.

If this is your first sour beer you will be tempted to taste the beer during aging. This is hard to avoid and the truth is that tasting is an important part of producing these kinds of beers. But there are a few practical rules that will benefit your end product.

Rule #1 is to taste very infrequently, if at all, for the first several months of aging and then when you feel that the beer is approaching the finish line limit your tasting sessions to once every month or two.

Rule #2 is to keep the pellicle intact to protect the surface of the beer from oxygen and to prevent/limit the potential of acetic acid bacteria from growing on the surface of the beer. One of the best ways to protect the pellicle is to drill a small hole in the head about 9 inches (23 cm) above the bottom of the barrel when it is laid on its side and to plug the hole with a stainless steel nail. As long as the hole is about 1⁄16-inch smaller than the nail you need not worry about the nail coming loose from the hole. This is your sample valve. Although a wine thief is a handy device, they can damage the pellicle and this really should be avoided at all cost. I have violated this rule in the past and strongly suggest using the sample nail project.


Can gluten proteins be removed by using a chlorinated cleaner when i want to use my normal brewing equipment to make gluten-free beer?
Lawrence Banachowski
Oxford, Michigan


As long as the equipment that touches wort or beer is cleaned immediately after use with an appropriate cleaner there will be no problem. I personally do not like chlorinated cleaners because they have the potential to pit stainless steel and have an odor that I find objectionable, but that is just my own pickiness.

The area that poses a challenge for gluten-free brewing is the dry ingredient side of the operation. At Springfield Brewing Company we store our pale malt in an outdoor malt silo and keep our specialty malts in bags stored in the mill room. A conveyor is used to transfer malt from the silo to the mill and a bucket elevator is used to lift special malts from the floor into the top of our mill. The milled malt flowing from our 4-roll mill with shaker box falls into the grist case where it is batched up before dropping it into the mash mixer.

Malt dust is a rich source of gluten proteins and is extremely difficult to clean for one simple reason. Malt handling equipment and dry mills are not designed to be cleaned with cleaning solutions. The goal with dry material handling is to keep the equipment dry, free of dust and to allow for ingredients to be cleanly brought into the operation. These measures greatly help to prevent problems in the dry side of the operation, and eliminate the need to use liquid cleaning in this part of the brewery.

When it comes to eliminating gluten proteins from a brewery, the design of the dry side makes the challenge very real to the commercial brewer. One obvious solution is to invest in dedicated equipment that is only used for the production of gluten-free products. In a commercial operation this solution may not be a realistic thing to do and is one of the reasons that gluten-free beers are not very common. At home the challenge is not nearly as difficult. You may need to buy a separate mill or buy a mill than can be disassembled and cleaned to address the issue. And anything you use to weigh, transfer or store dry materials needs to be thoroughly cleaned before use.

Issue: September 2012