Author: Ray Found

In Yeast: The Practical Guide To Beer Fermentation, authors Chris White and Jamil Zainasheff posit,

One of the most important measurements, especially in terms of fermentation, is pitching rate. Without consistent pitching rates, flavor can change significantly from batch to batch. What are the consequences of overpitching or underpitching? In general, underpitching affects flavor more, while overpitching negatively affects yeast health more over generations. However, both can result in a less than ideal fermentation with high levels of diacetyl, acetaldehyde, and low attenuation.

Indeed, making yeast starters to dial in precise pitching rates has become a norm with many brewers attributing significant improvements in the quality of their beers to the practice. The existence of myriad calculators designed to help brewers determine what size starter is required to propagate specific cell counts is evidence of this shift in understanding, and the beer people are producing today is ostensibly better than it’s ever been, so it must be working!

Interestingly, results from a previous xBmt found participants were unable to reliably distinguish an ale fermented with a single pack of yeast (~56 billion cells) from the same beer fermented with yeast propagated in a starter (~237 billion cells), suggesting underpitching may not be as detrimental as many believe in otherwise ideal conditions. This is likely possible due to advancements in the yeast manufacturing process that has allowed brewers to use remarkably pure and viable cultures.

Unlike ales, lagers demand clean yeast character and subtle flavors, which in addition to the fact they’re traditionally fermented at cool temperatures, has led to the largely accepted notion that they “require” a ton of yeast, around double the recommended amount for ales. As a lager beer brewer myself, I’ve often wondered about this purported requirement, namely whether it’s really necessary to double up on yeast to achieve the results I’m after, but also what impact overpitching might have on my beer. Unable to find satisfactory answers elsewhere, I decided to test it out for myself!

| PURPOSE |

To evaluate the differences between an underpitched and overpitched lager beer of the same recipe.

| METHODS |

Saflager W-34/70 was chosen for this xBmt not only because it’s known for being the most popular lager yeast strain in the world and thus applicable to many brewers, but the fact it is a dry yeast would presumably make cell count predictions more accurate. While researching dry yeast for this xBmt, I discovered there seems to be some confusion over how many cells are actually contained in each pack. While Fermentis reports 69 billion cells per pack of yeast (6 billion per gram), counting exercises such as the one performed by Sean Terrill suggest a count closer to 230 billion cells per pack (20 billion per gram), which supports Jamil’s claim that Fermentis’ counts are a lower-bound guaranteed amount. I deferred to the latter for this xBmt.

Since a version of my Märzen recipe is frequently on tap at Stone Church Brewing, I don’t feel the need to make it for myself, so I’ve been gradually adapting the recipe towards the Festbier style, a style I figured would highlight any differences caused by the variable in this xBmt.

Festbier 2016

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 33.4 IBUs 7.0 SRM 1.056 1.013 5.6 % Actuals 1.056 1.013 5.6 % Fermentables Name Amount % Pale Malt, 2 row (Gambrinus) 7.625 lbs 64.89 Vienna Malt (Gambrinus) 2.375 lbs 20.21 Munich Light 10L (Gambrinus) 1.375 lbs 11.7 Honey Malt 6 oz 3.19 Hops Name Amount Time Use Form Alpha % Hallertau Magnum 14 g 60 min Boil Pellet 12.1 Saaz 60 g 15 min Boil Pellet 3 Yeast Name Lab Attenuation Temperature Saflager Lager (W-34/70) DCL/Fermentis 75% 48°F - 59°F

I started the day prior to brewing by turning my highly chlorinated, rock hard Corona City water into nearly pure, mineral devoid RO, perfect for building a water profile upon.

The following afternoon, I weighed out and milled the grains for a single 11-gallon batch while my strike water heated.

Once it reached a few degrees above the recommended temperature, I poured the strike water into my mash tun for a brief pre-heat then added the milled grain and gave it a good doughball bustin’ whisking.

Mash-in complete, I found the temperature settled just above my target.

I set my mash timer for an hour then took the downtime to make up a “hop kit” so that each addition was ready to go. I also drank a Swami’s IPA… mmmmm, Swami’s.

After the mash rest, I transferred the sweet wort to my kettle where it was boiled for 60 minutes.

At the end of the boil, I quickly chilled the wort to just above the temperature of my groundwater then took a hydrometer measurement showing I’d hit my intended OG.

The 6 gallon PET carboys were placed in my cool chamber where they remained overnight to drop to my target fermentation temperature of 56°F/13°C. With the temperatures stable, it was time to introduce the variable. Various yeast pitch rate calculators recommended around 430 billion cells for 5.5 gallons of 1.056 OG lager wort. Assuming the 20 billion per gram estimate is correct, a single pack of yeast contains would lead to a 50% underpitch while 5 packs would result in a 250% overpitch. I prepared both sets of yeast by rehydrating them in 95°F/35°C water then allowing to cool to around 60°F/16°C before pitching.

The overpitched batch was beginning to develop a kräusen about 30 hours post-pitch while the underpitched beer still looked eerily like wort.

Another day later, the overpitched beer was in full-swing as the underpitched batch appeared as though little was going on.

The underpitched beer was finally making some progress by the third day, just a couple days behind its overpitched counterpart.

Both beers were fully engaged and ripping along nicely 4 days post-pitch, which is when I began inching up the temperature to promote a complete fermentation.

I observed no visible signs of activity in either batch at 12 days from the kettle and took hydrometer measurements revealing both had reached the same predicted 1.013 FG.

The beers were cold crashed, fined with gelatin, racked to kegs, then burst carbonated. By data collection time, both had cleared equally well and shared a pleasing amber hue.

| RESULTS |

A total of 15 people of varying levels of experience participated in this xBmt, many during a BeerMe Brew Club meeting, and all blind to the variable being investigated. Each taster was served 1 sample of the underpitched beer and 2 samples of the overpitched beer in different colored opaque cups then asked to select the unique sample. In order to reach statistical significance with this number of participants, 9 (p<0.05) would have had to make the accurate selection. In the end, only 5 (p=0.60) were able to do so, which is exactly congruent with chance, suggesting tasters were unable to reliably distinguish a lager fermented with approximately 50% the recommended amount of yeast from a similar lager fermented with nearly 250% the recommended amount of yeast.

My Impressions: I keep tricking myself-– on a few occasions, I’d pour myself samples of both beers to evaluate, initially think I could tell a difference, then wait a few minutes before taking more sips only to find what I thought was different had switched cups! My performance on “blind” triangle tests was, wait for it, 1 out of 3, exactly the same as participants. I could not reliably distinguish either beer from the other, even in side-by side tastings, even after tasting them as different then simply shuffling the cups, forcing me to accept that any differences I thought I perceived were likely in my head.

| DISCUSSION |

I’ve fermented many batches of lager with a single pack of dry yeast, which by conventional standards means I’m underpitching, yet my experience has been hugely positive. No major off-flavors, I’ve even won a few awards. In chatting with the other contributors about these results, I learned I’m not alone in this camp. While I’ve little doubt yeast pitch rates are important for healthy fermentation, it seems to me the relationship between cell count and quality of the finished beer including attenuation and overall character isn’t as linear as I once thought. Especially since several yeast pitch xBmts have yielded non-significant results, and this direct comparison of pitch rates is similarly insignificant.

Despite the fact tasters were unable to reliably distinguish between the underpitched and overpitched beers, there were some differences. For example, the underpitched batch took nearly 2 days longer to show signs of active fermentation compared to the overpitched batch, which may be viewed by some as reason enough to pitch more yeast in order to decrease the risk of contaminants having their way. A more practical difference can be seen in price– at $6.00 per pack of yeast, the underpitched batch cost $24.00 less than the overpitched batch. Of course, the amount of yeast used in the overpitched batch is unreasonably high, the fact it was perceptibly no different than the underpitched batch suggests pitch rate may be an area of diminishing returns.

Admittedly, I’ll use these results help to assuage the twinge of guilt I feel when pitching a single pack of yeast into a batch of lager when all calculators agree it “requires” two packs. This is in no way a recommendation that others follow suit, as this is a single data point using a specific strain of yeast and thus the results may not be generalizable. But hey, $6.00 is $6.00!

Please share your thoughts on pitching rates or the results of this xBmt in the comments section below!

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