Author: Marshall Schott

In the last iteration of this xBmt, we found that a beer fermented with relatively old slurry harvested directly from a previous fermentation and propagated in a starter was largely indistinguishable from the same beer fermented with a fresh pack of the same yeast strain. Afterwards, I received a ton of feedback from readers asking if I’d ever considered doing a similar comparison without making a starter, but rather pitching the un-rinsed old yeast slurry directly into a 5 gallon batch of wort. Indeed, it was on the list. I reached out to a few of these folks asking if they’d ever attempted such a practice, a couple reported they had with success, but the large majority said they were hesitant to try out of fear of fucking up an entire batch of beer.

A fear I’ve come to embrace with only scant hesitance.



If you’re wondering why a brewer might be interested in this method, it’s likely because they’re looking to simplify their brewing process– if good beer can be made with un-rinsed yeast slurry without going through the trouble of making a starter, and that yeast was stolen from the bottom of a previous batch, then why not? Plus, reusing yeast is cheaper than purchasing a fresh pitch for every batch. Some of the arguments against this method, which I can’t find any valid practical evidence to substantiate, have to do with carryover of character from the previous fermentation, off-flavors caused by autolyzed cells, over- or under-pitching, and increased potential for contamination. That last one seems obvious, it makes sense to me that risk of contamination is positively correlated with increased handling. Those other arguments I’m not convinced hold much water, if any. At least yet. But I’m certainly open to changing my mind.

| PURPOSE |

To evaluate the differences between a split batch of the same wort where half was fermented with a 3rd generation of old un-rinsed yeast harvested from a prior batch and the other half pitched with fresh yeast.

| METHODS |

I’d recently registered 2 beers for the 2015 BrewUnited Challenge, a Dunkel and a Kölsch, a couple styles I make relatively often and typically do so without much thought. However, given the rather strict guidelines for this particular competition, I was forced to do something I’d never done before– toast my own malt. A couple weeks before brewing, after settling on the recipe, I spread 2.5 lbs of German Pils malt on a cookie sheet while preheating my oven to 350°F. I found an interesting blog article all about home toasting malt that suggested leaving the malt at this temp for 30 minutes, turning it a few times throughout, in order to achieve approximately 250 °L.

I was thrilled with my home toasting job… my wife, not so much. This process created quite the aroma, not necessarily bad if you’re into the scent of burnt popcorn lingering for days. Yeah, this first attempt was also my last, at least using the kitchen oven. I placed the toasted grain in a paper bag, crimped the top, and let it rest until my planned brew day a couple weeks later, at which point the smell in my house had fully dissipated.

If you think the recipe looks weird, it’s the fault of the folks who came up with the competition rules. I was actually pretty stoked to see how this would turn out.

BrewUnited Challenge Dunkles

Batch Size Boil Time IBU SRM OG FG ABV 11 gal 60 min 38 4.5 1.048 SG 1.010 SG 4.9%

Fermentables

Name Amount % German Pils Malt 13 lbs 72 Home Toasted Pils Malt 2 lbs 6 oz 13 Gambrinus Munich 10 2 lbs 11 Flaked Wheat Malt 8 oz 3 Crystal/Caramel 60 4 oz 1

Hops

Name Amt/IBU Time Use Form Alpha % Northern Brewer ~19 IBU FWH Boil Pellet 10 Czech Saaz 40 g/2 IBU 10 min Boil Pellet 3

Yeast

Name Lab Attenuation Ferm Temp Saflager 34/70 Fermentis 85% 66°F

The night prior to brewing, I measured out my grains and ran them through my new Monster Mill MM3… holy moley, this thing is a monster! I intend to give it a full review soon, until then, I’m perfectly comfortable recommending it to anyone interested in a high quality mill that provides a consistent crush very quickly (10 lbs in ~1 minute).

With the grain milled, I collected my entire volume of brewing liquor, which I began to heat upon waking early the following morning. I proceeded with my routine single infusion mash process and hit my target saccharification temperature of 150°F on the nose.

I allowed the mash to sit for an hour, briefly stirring every 15-20 minutes, which I’ve found has improved the consistency of my efficiency.

I generally pull a small sample of wort from the mash about 5 minutes in to measure the pH. For this batch, I was also super curious how well my home toasted malt would impact the color. It looked pretty spot on to me.

I quickly chilled the sample and took a pH measurement to discover I was just a few points shy of my 5.3 target. Not too shabby for guesstimating the impact of the toasted Pils malt.

My mash timer beeped and I collected the wort, nearly 13 gallons worth in my 14.5 gallon kettle, which was easily managed with the help of FermCap-S.

I added a relatively small amount of hops during the 60 minute boil then chilled the wort in under 12 minutes to 6°F above my groundwater temperature, which during this time of year is an annoyingly warm 76°F.

Separate 6 gallon PET carboys were filled with equal amounts of warm wort, which was gently stirred throughout racking to ensure similar amounts of kettle trub in each. The full fermentors were placed in a cool chamber and left to finish chilling to my target fermentation temperature of 50°F, this took about 6 hours. I then prepared the yeasts to be pitched, rehydrating the fresh sachet for 20 minutes and decanting the jar of sloppy old slurry that’d been warming up in my garage for the last hour or so.

Each yeast was pitched into its respective carboy.

I’ve grown used to the longer lag times that occur when using dry yeast compared to liquid and noticed initial signs of activity an expected 3 days post-pitch. But only in one fermentor.

The sloppy old slurry batch appeared to be doing nothing. At all. I began to wonder if perhaps the harvested yeast had somehow puttered out when I checked the next day.

A full 5 days in and the fresh yeast batch was kicking ass while the beer pitched with sloppy old slurry had absolutely no indications of fermentation activity.

A hydrometer measurement confirmed my concern– the SG of the sloppy old slurry batch hadn’t dropped at all. Would this end up being a failed xBmt?

It was at this point I had to make a decision, as I was heading to Seattle for 11 days to help my father in law recover from a stroke. Usually, this is the point I’d start ramping the temperature up, but the problem was the sloppy old slurry clearly hadn’t progressed into active fermentation. Ultimately, in order to give this xBmt a fighting chance, I chose to disengage the quick lager profile in my Black Box temp controller and allow both beers to remain at 50°F the duration of my trip. Upon returning, I was anxiously optimistic and took hydrometer measurements.

Back in business! Finally, I raised the temp of my chamber to 70°F for a seemingly unnecessary diacetyl rest, crashed to 30°F the following evening, then fined with gelatin a day later. When it came time to package the beers, I removed the carboys from my cold chamber and immediately noticed a difference in trub levels.

The trub cake in the sloppy old slurry batch was obviously thicker and contained much more debris. I was curious how this might impact things later on. I proceeded to rack the beers to kegs.

After 24 hours on 40 psi of CO2, the beers were perfectly carbonated. Data collection occurred the following weekend.

| RESULTS |

The participant pool for this xBmt consisted of 20 people including 7 BJCP judges, a couple professional brewers, experienced homebrewers, and dedicated craft beer junkies, all completely unaware of the variable being tested. Achieving statistical significance with this sample size would require 11 participants (p<0.05) to correctly identify the different beer in the triangle taste. Each blind taster was provided 3 samples of beer, 2 from the sloppy old slurry batch and 1 from the fresh yeast batch, then instructed to select the one that was different. Those who made a correct selection in the triangle test were asked to complete a brief comparative evaluation of the 2 different beers. In the end, only 5 participants (p=0.785) were capable of accurately distinguishing the beer fermented with fresh yeast from the one fermented with sloppy old slurry, a number consistent more with chance than perceptive ability.

A review of the comparative evaluation data from those who were correct in the triangle test yielded little if any meaningful information with no consistency between comments. Some thought the fresh yeast beer was more malty, others swore the sloppy old slurry beer had more malt character. Preferences of the 5 correct participants were also split between the batches.

My Impressions: I was able to distinguish these beers the very first time I poured them, didn’t even have to taste or smell them. Because they looked different. I was actually rather surprised how much clearer the sloppy old slurry beer was than the fresh yeast beer the first couple days after kegging, something I hypothesize may be a function of the small amount of gelatin carried over from the slurry’s prior fermentation. After about 4 days in the keg, the beers shared similar levels of clarity and when served quasi-blind in opaque cups, my prowess evaporated, I was wholly unable to reliably distinguish the different beer in multiple trials. If I had to choose a favorite, I’d go with whichever one was in the glass in front of me.

| DISCUSSION |

This xBmt left me sort of puzzled, maybe amused is the more appropriate adjective, not necessarily because slurry produced a beer that wasn’t much different than the same beer fermented with fresh yeast, I actually sort of expected this result. Rather, the fact the lag observed in the sloppy slurry starter beer didn’t seem to have any noticeable impact on the flavor is, well, amusing. I’m only slightly ashamed to admit that the time between pitching and first signs of a krausen is sort of anxiety provoking for me, I’m always concerned some other organism is going to infiltrate and ruin my beer or that the yeast is going to produce off-flavors from being over-stressed. But this didn’t happen, which suggests my sanitation practices are at least decent enough… and I’m likely the one who is over-stressed.

Despite the fact these results corroborate the experiences of some highly trusted homebrewers I’ve talked with, I’m not quite ready to start ditching the practice of preparing sloppy old yeast in a starter prior to pitching, if only because it added 3 days to my turnaround time and I’m impatient. What these results have done is bolstered my confidence that reusing un-rinsed slurry doesn’t guarantee bad beer. I absolutely plan to utilize the vitality starter method when pitching slurry in the future, it seems to be an ideal application for this. Either way, I won’t be advocating for this method, though for those who pride themselves on keeping their gear optimally clean and sanitized, it’s fully possible pitching slurry direct without the aid of a starter, even after being stored for a few months, will produce a fine batch of beer.

Are you a proponent of pitching sloppy old slurry directly? If so, or if you’ve other thoughts/experiences regarding this method, please feel free to share in the comments section below.

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| Read More |

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7 Considerations for Making Better Homebrew

List of completed exBEERiments

How-to: Harvest yeast from starters

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