Author: Marshall Schott

Over the last few years, it’s become commonplace for homebrewers to propagate yeast in a starter to ensure a viable pitch, a simple process consisting of fermenting a relatively small amount of wort, usually made from extract, which is then used to ferment an actual batch of beer. Starters for standard 5 gallon batches of moderate OG ale are often small enough that most would contend pitching the entire volume has an unnoticeable impact on the flavor of the finished beer. However, there are times larger starters are recommended by pitch rate calculators, such as for lagers or higher OG beer, resulting in a greater volume of liquid sitting atop the creamy yeast cake. What to do with this supernatant has become yet another issue of debate in brewing circles with some swearing any off-flavors present will be metabolized during fermentation while others decant out of fear of imparting undesirable flavors.

I first ran into this issue years ago when making a cool fermented lager that called for a 2.8 liter starter, which I calculated as being approximately 14% the volume of the wort I’d be pitching it into. This seemed like a lot to me, certainly more than I was comfortable adding without evidence suggesting it wouldn’t matter, and unfortunately my search for solutions yielded conflicting results. Eventually, likely inspired by something I read or heard somewhere else, I adopted the heuristic I still use today– decant any starter that’s over 5% the volume of the beer, which is simple enough to remember since 5% of 5.25 gallons is almost exactly 1 liter.

Indeed, this rule of thumb has served me well, I’ve pitched hundreds of batches with 1 liter starters that have come out fine. It wasn’t until after being asked about the necessity of decanting larger starters that I realized I’d been engaging in an arguably more complicated process based on nothing more than a hunch with perhaps a sprinkle of an appeal to authority. Truth is, the decanting process does add a few steps that I’d be happy to forgo if I knew it wouldn’t screw up my beer. And I’ll admit, I still cringe a little when decanting starters knowing the supernatant contains millions of healthy yeast cells ready to turn my wort to beer. With this in mind, I was finally inspired to test it out for myself!

| PURPOSE |

To evaluate the differences between two beers of the same recipe fermented with either a decanted or full starter.

| METHODS |

In an effort to ensure any differences caused by the variable were well expressed, I thought it only prudent the beer not be so characterful as to hide any effect, hence I opted to make my Munich Helles, the kits of which were graciously provided the great folks at Love2Brew.com.

For this batch, rather than using the yeast I first brewed it with, WLP029 German Ale/Kölsch, I went with Saflager W-34/70, a new favorite due to its ability to produce clean lager character even when fermented at ale temperatures.

While it’s commonly said dry yeasts don’t need to be propagated in a starter, I did exactly that 3 days before brewing, making a single large starter from 1 pack of yeast in order to keep things as similar as possible between each batch.

When brew day arrived, my neighbor Tim milled the grain while the mash water was being heated to the proper strike temperature.

Once the strike water was ready, I transferred it to my cooler MLT for a brief pre-heat before stirring in the grist, the temperature settling in precisely where I wanted it to be.

About 10 minutes into the mash, I pulled off a small sample to make sure the pH was where I preferred for this beer. On the nose!

Following the 60 minutes saccharification rest, I collected the first runnings, added in the batch sparge addition of water, and gave it a good stir before running off the rest of the sweet wort.

As the wort was coming to a boil, I split the single 3.4 liter starter into another flask, swirling it vigorously before doing so to ensure homogeneity. These equal sized starters were then placed in a 32˚F/0˚C freezer where they were left to cold crash for the remainder of the brew day.

The wort was boiled for 60 minutes with hops added at the times stated in the recipe.

Af the conclusion of the boil, I rapidly chilled the wort to 78˚F/26˚C, just a few degrees warmer than my summer groundwater temperature.

I then transferred equal amounts of the chilled wort to separate fermentors, stirring occasionally throughout to make sure similar amounts of kettle trub made to each one.

The fermentors were placed in my cool chamber where they sat for 5 hours before stabalizing at my target fermentation temperature of 66˚F/19˚C. A this point, I took the flasks of yeast that had been crashing in the freezer for nearly 8 hours and very gently decanted one into the other, leaving behind the slurry and enough supernatant to facilitate easy pitching.

By my observation, the full starter was approximately 2600 mL larger than the decanted starter, presumably enough to produce a difference if indeed there was going to be one. I let the starters sit in my warm garage for about 30 minutes to warm up a bit before pitching to avoid shocking the yeast. I returned 10 hours later and observed the airlocks on both batches bubbling like made, which is far quicker than when I’ve pitched rehydrated dry yeast. As far as I could tell, both beers fermented similarly and showed a demonstrable decrease in activity at 5 days in. I raised the chamber temperature to 70˚F/21˚C and left the beers alone for another 5 days before taking a hydrometer reading to check if FG had been reached.

While a potential result of the variable, I view a 0.001 SG difference is within the margin of error. With all signs of fermentation gone, I cold crashed, fined with gelatin, then kegged the beers.

The full kegs were burst carbonated for 15 hours before being reduced to serving pressure. When it came time to collect data the following weekend, both beers were clear and carbonated.

| RESULTS |

In all, 20 people of varying experience levels participated in this xBmt. Each participant was served 2 samples of the full starter beer and 1 sample of the decanted starter beer then asked to identify the sample that was unique. Given the sample size, 11 tasters (p<0.05) would have had to correctly identify the decanted starter sample as being different in order to reach statistical significance. A total of 8 tasters (p=0.34) accurately identified the unique sample, indicating panelists were unable to reliably distinguish a beer fermented with a 3.1 liter starter from the same beer fermented with a 300 mL starter.

My Impressions: In multiple attempts over multiple days, I was unable to tell these beers apart, despite my slight bias against pitching starters over 1 liter and knowledge of the variable. Both tasted like the non-traditional, heretical Helles I first fermented with WLP029, though they required even less time being fermented at ale temperature with W-34/70.

| DISCUSSION |

As I trust anyone who has been at this hobby for awhile can attest, there are times we get lazy and/or forgetful, if you know what I mean, which can lead to the making of mistakes. I’ll admit I’ve pitched starters that were over the 1 liter mark on more than one occasion, often regretting my decision to do so the following morning, though failing to notice any real detriment in the finished beer. Still, I wasn’t convinced differences in starter volume had no qualitative impact and was surprised not only that participants were unable to reliably distinguish the beers in this xBmt, but that I couldn’t either. I’ve tasted supernatant before, it’s pretty gross, yet none of the esters and oxidation flavors I usually detect in it were at all present in the finished beer.

The methods we use allow us to test whether certain variables produce a perceptible effect, though limit our ability to provide reasons for what’s going on. Relying on speculation I’ve read from others, one might presume the flavors and aromas produced during the starter process are in some way metabolized when the yeast is reactivated during primary fermentation. It seems to make sense given what we know about fermentation in general, though until there’s more evidence, I’m quite content to answer “I don’t know.”

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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