New homebrewers are bombarded with the “always” and “never” rules. “Always be sure to let your beer finish fermenting before bottling” and “never add too much priming sugar” are two examples. While those are easily proven to be true, as anyone who has had exploding bottles can attest, there are other rules that have been handed down from one generation of homebrewer to the next that are not so quickly validated. As homebrewers become more advanced, many begin to wonder which elements of common homebrewing wisdom are true and which are simply reflections of the way things have always been done. 

Debating these customs over a pint or two is a popular pastime among homebrewers. Wherever we gather, whether at club meetings or online, debates on brewing practices rage. Discussing the pros and cons of various practices is fun, but without evidence one way or another, talk alone — even when backed by anecdotal evidence — will not settle these ongoing debates. In an effort to test the soundness of some of these brewing rules, Brew Your Own teamed up with Basic Brewing Radio, a podcast on homebrewing (found at www.basicbrewing.com), to plan a series of experiments. We want our experiments to be collaborative, easy to execute and capable of yielding a clear result.

By encouraging collaboration among many homebrewers, we have the possibility of seeing an experimental result replicated many times over. If multiple homebrewers perform an experiment and most get comparable results, this will allow us to place more confidence in the results of the experiment. 

To encourage as many homebrewers to participate as possible, our experiments will be simple to execute, require little advanced equipment and be able to be performed in a relatively short amount of time, so that results can be reported quickly. In this series of experiments, we will try to walk the line between designing experiments that are simple enough to encourage participation, but still controlled enough to yield worthwhile results.

Finally, we want to pick experimental questions for which we can get clear results. One key aspect of this involves what data is collected. Obviously, the most important aspects of beer are its flavor and aroma. However, experiments that involve judging the merits of one beer versus the other have the potential to get mired in subjective judgements. We wanted our experiments to include, where possible, actual measurements. These could include such things as original gravity (OG), final gravity (FG), time or pH. Where tasting data would be a part of the experiment, we wanted to make sure the instructions to the tasting panels would be clear. An experiment in which you ask a narrow question, such as “can you taste a difference between these two beers” is better than one in which you ask a nebulous question such as “how do these two beers compare?” 

James Spencer, producer of the podcast, polled his Twitter followers (@basicbrewing) and received a wide range of suggestions. In the end, Chris and James chose the question, “Does leaving your beer on the primary yeast for a couple of extra weeks ruin it?”

A decade ago, the rule of the day was that beer must be racked off the primary yeast as soon as possible to avoid the off flavors associated with autolysis – the process of yeast degradation and decomposition. It was said that more than a week on the primary yeast was risking horrible meat-like or rubber-like off flavors and aromas. Racking to secondary was seen as necessary as soon as active fermentation completed.

But, is this true? What would happen if the beer was left on the primary yeast for an additional couple of weeks?

What We Did

To address our experimental question, we came up with three possible experimental designs and allowed each participant to choose the experiment of their choice. We also let participants choose their own beer styles and yeast.

One Carboy Experiment

For the easiest version of the experiment, the participant only needed to brew one batch of beer. The brewer would ferment the beer as usual, making sure to take an OG reading. Once it finished, he or she would rack half of the beer to his or her bottling bucket or keg, then return the airlock to the carboy and let the remaining half sit for two weeks on the yeast. After the two weeks, the brewer would package the second half of the beer. After a couple weeks of conditioning, the brewer would take the FG of each beer and also taste them side by side.

Two Carboy Experiment 

Ideally, in an experiment, the only difference between different trials should be the experimental variable. In our case, this would be the contact time with the yeast. But, if you look at the design of the first experiment, this isn’t exactly the case. Half of the batch gets packaged before the other, giving it more time to condition. With a little extra effort, we can control for this variable.

For the two-carboy version of the experiment, the brewers would again brew their beer as usual, but have a second sanitized carboy ready as the beer ferments. Once fermentation ceases, they would rack half the beer to the second carboy and let them both sit for two weeks. Then they would package them both at the same time.

Three Carboy Experiment 

When most homebrewers leave their beer in primary, they don’t open the carboy, as happens in the first two experiments when we rack out half the contents. So we also had an experimental option that took that into consideration. In this option, the brewer would make the wort and split it evenly between two carboys. He or she would then pitch the same amount of yeast to each carboy and let them both ferment. When the fermentations cease, the brewer would rack one of the carboys to secondary and leave the other on the yeast. This more closely mimics the differences the beer would experience in real-life situations.

The data we asked the participants to collect were the original gravity (OG) of the beer and the final gravities (FG) of the two trials. We also asked them to taste the beer and see if they could tell a difference. Secondarily, we asked them to describe any differences. We also encouraged them to report any observations they found interesting. These could have included things such as differences in beer color, foam retention or any other beer characteristic. We felt that, if leaving your beer in primary for two weeks was as bad as some people imply, we should be able to get a clear cut result. If leaving the beer on the yeast led to significant off aromas or flavors, all the tasters would have to do is distinguish between bad beer (with pronounced meaty, brothy or rubber-like characteristics) and good beer (which lacks those notes).

Results

For his entry into the experiment, James brewed a very simple wheat beer, made with six pounds of dried wheat malt extract, 1.25 ounces of UK Fuggles pellet hops (boiled for 60 minutes) and fermented with Safale US-05 dried yeast.

At the two-week point in fermentation, James bottled four bottles off the primary fermenter, using Muntons Carb Tabs to prime. Also at that time, he racked half of the beer into a secondary carboy, leaving the rest on the primary yeast. Two weeks later, James bottled four bottles each from the primary and secondary fermenters, priming in the same method as before. Twenty-five days later, Steve Wilkes joined Chris and James to crack open the brews and test the results. (You can hear their discussion on the May 28th episode of Basic Brewing Radio).

The beers were presented in a blind fashion to Steve and Chris. All three tasters thought the differences between the three beers were extremely insignificant.

Chris said that all three samples were “very similar” with a “clean” flavor. According to Chris, the beer bottled at two weeks had the least amount of body. The beer left on the primary yeast for four weeks had a very slight “meaty” or “broth-like” character, while the beer that had been racked to secondary was crisper, or — as he put it — the “zippiest.”

While Steve thought the beer left on the primary yeast was the most different, it was the beer that he preferred. He described it as “most fruity.”

James thought the beer bottled at two weeks had a sharper and cleaner character. While he thought the beer racked to secondary had a more fruity quality, James felt it was “cleaner” than the beer left on the primary yeast for the full time period – a beer he described as very slightly “nuttier.”

The differences in aroma, color, carbonation and mouthfeel were negligible.

Missing in the discussion altogether were off-putting, obvious flaws in the beer. While James and Chris used the adjectives “meaty” and “nutty,” they both felt that they had to search intently to find those characteristics, and may not have noticed them otherwise. There wasn’t any of the “rubbery” character most often said to be a characteristic of autolyzed yeast.

Similarly, racking to secondary doesn’t seem to have had a significant effect on the final gravity of the wheat beer. At the time of racking, the beer measured 1.014 specific gravity. Two weeks later, the beer that was left on the primary stood at 1.012, while the racked beer weighed in at 1.011 — a difference of 0.001 between the two approaches.

Twelve homebrewers from four countries responded to the call to repeat the experiment on their own and submit the results via an online form. Their results are summarized in the sidebar on page 52. Remarkably, each of the twelve used different ale yeast strains. Also remarkable was the fact that none of the participants reported that his beer had been ruined by off flavors typical of that caused by autolysis.

The most extreme example was from R.J. Parker of Mountain View, Hawaii. R.J. had transferred a gallon of fermenting beer from his primary bucket to avoid blowoff. He had let the gallon ferment and sit on its primary yeast for 40 days more than the beer that had been in the bucket.

R.J. reports that the beer left on the yeast was “very clear and slightly mellower.” He also says, “it’s a bit more fruity, but differences are very slight. The difference between the two batches is quite subtle.”

The twelve experiment participants were split on whether the process yielded significant flavor differences. Six said there was either no or slight flavor difference, while five reported definite flavor differences. One was disqualified because coriander was added to one sample and not the other. However, in his submission, Hugh Brown of New Westminster, British Columbia, commented that both samples were quite good.

Of those that described a flavor difference, five reported that the racked beer tasted “cleaner” or “smoother.” Adam Ross of Davenport, Iowa said his transferred sample tasted “cleaner,” but he preferred the North English Brown that had spent more time on the yeast.

“My final verdict is that I preferred the beer that remained on the yeast,” said Adam, “which is a little disappointing as I’ve been racking every beer I have made for almost two years now.”

Jerry Marowsky of Oak Creek, Wisconsin also preferred the half of his American Pale Ale that had spent more time on the primary yeast, but he thought it tasted “cleaner.”

“I believe letting the beer sit on the yeast for a slightly extended time helps the beer mellow and cuts down on cellaring time,” said Jerry.

George Helfers of St. Louis, Missouri brewed a Blonde Ale. “The batch left on the yeast had definite flavor and aroma differences,” George said. “I detected a bready, grainy aroma, a more pronounced hop bitterness, and overall it just was not as ‘smooth’ as the first batch. I do believe that the conditioning of the first batch may have contributed to many of the differences. Therefore, I can’t say for certain if remaining on the yeast affected the beer in a profoundly noticeable way.”

Those expressing a preference for one sample or the other were divided equally: three on each side of the fence.

As you can see by the sidebar chart, leaving the beer in the fermenter apparently didn’t make a significant difference in the gravity of the beer over the additional two weeks.

Six of the participating brewers noted differences in the carbonation or head retention of the beers. Four said the racked beers had better carbonation, while two leaned toward the beers that remained on the yeast. However, it should be noted that some of these beers had more time in the bottle or keg to condition and develop better carbonation levels.

Only one brewer reported a significant difference in the color of the samples, saying that the beer that remained on the yeast was slightly darker. Again, none of the participating brewers reported off flavors that spoiled the samples left on the primary yeast for an additional two weeks.

Conclusions 

The results of this experiment are clear — leaving your beer on the primary yeast for a moderate amount of time (two to four weeks) does not ruin it. In our experiment, the flavor difference between the trial beers was very subtle and no brewer reported that the beer left on the yeast was marred by excessive off flavors. Leaving the beer on the yeast does, however, change the character slightly. Interestingly, participants were split over whether this improved or detracted from the beer. It is important to note that all of the beers in the study were ales. It is possible that lager beers — which are fermented with different yeast strains and at colder temperatures — might respond differently. In addition, off flavors or aromas may result from a longer exposure to yeast. 

There are elements of our experimental design that could be criticized. For example, James performed a variant of the two-carboy experiment and disturbed the beer sitting on the yeast twice. Also, there was a variety of experimental approaches among the participants. However, we feel the consistency of the results, across ale strains and experimental approaches, shows that our result is strongly supported. Unless our experimental design somehow suppressed the development of brothy or rubber-like off characters — something we strongly doubt — we think brewers can be confident that moderately long contact with yeast will not spoil a batch of homebrewed ale. It does, however, cause a slight difference in the beer’s taste.  

Our next experiment will ask the question “How does pitching rate affect beer character?” Visit the Basic Brewing website or Chris’s blog on byo.com for a description of the experiment. We invite all interested brewers to join us in tackling this topic.

James Spencer is the host of Basic Brewing Radio and Basic Brewing Video. Chris Colby is Editor of Brew Your Own.