exBEERiment | Yeast Pitch Rate: Yeast Cake vs. Direct Pitch In A Vienna Lager

Author: Martin Keen

Of the several factors that contribute to a high quality batch of beer, one that gets a lot of focus is yeast pitch rate, which is largely a reference to viability, or the amount of living cells in a given population of yeast. While pitching too little yeast, known colloquially as underpitching, is associated with a number of undesirable off-flavors, overpitching is often said to be less-than-ideal though has a much lower risk of negatively impacting beer characteristics.

Brewers rely on a few ways to ensure yeast viability, one of which involves taking yeast recently used to ferment another batch and pitching it into fresh wort. On the commercial scale, this is often done by pulling a specific amount of yeast slurry from the bottom of the fermenter and pitching “cone to cone,” whereas the simplest option for homebrewers is to transfer fresh wort onto the entire yeast cake from a prior batch. This method may be cause for pause for some wary brewers, as it will almost certainly qualify as an overpitch for even moderate strength lagers and ales.

Yeast is the most expensive ingredient in a batch of beer, and hence it makes sense why many brewers adopt techniques to extend the life of an original pitch. While I’ve overbuilt starters and repitched smaller amounts of yeast slurry from one batch to another, I was curious how overpitching by fermenting on an entire yeast cake might impact a Vienna Lager and designed an xBmt to test it out.

| PURPOSE |

To evaluate the differences between a Vienna Lager fermented with the yeast cake from a previous batch and one fermented with a direct pitch of fresh yeast.

| METHODS |

I went with a simple Vienna Lager recipe for this xBmt in hopes any impact of the variable would be easily perceived by tasters.

Overstaffed

After collecting the full volume of filtered tap water for a 10 gallon/38 liter batch, adjusting it to my desired profile, and heating it up, I milled the grain then mashed in.

When the 60 minute mash rest was complete, I removed the grains and boiled the wort for 60 minutes with hops added at the times listed in the recipe.

At the completion of the boil, I quickly chilled the wort with my Exchilerator MAXX CFC.

A refractometer reading indicated the wort was at my target OG.

At this point, I transferred identical amounts of wort to separate fermentation kegs, one of which contained the entire Imperial Yeast L13 Global yeast cake from a prior batch of pale lager, while the other was pitched with a fresh pouch of the same yeast.

The filled fermentation kegs were placed next to each other in a chamber controlled to 64°F/18°C.

While fermentation kicked off within a couple hours for the batch fermented with a yeast cake, it took a bit longer for the beer that was direct pitched. Both were left alone for 4 weeks, at which point signs of activity were absent, so I took hydrometer measurements showing a slight difference in FG that went against my expectations.

At this point, I cold crashed the beers overnight before pressure-transferring them to fresh CO2 purged serving kegs that were placed on gas in my keezer. After a 3 week lagering period, the beers were carbonated and ready for evaluation.

| RESULTS |

A total of 20 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the beer fermented with a yeast cake and 1 sample of the beer fermented with a direct pitch of fresh yeast in different colored opaque cups then asked to identify the unique sample. While 11 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, 12 did (p=0.013), indicating participants in this xBmt were able to reliably distinguish a Vienna Lager fermented with the yeast cake from a previous batch from one fermented with a direct pitch of fresh yeast.

The 12 participants who made the accurate selection on the triangle test were instructed to complete a brief preference survey comparing only the beers that were different. A total of 4 tasters reported preferring the beer fermented with the yeast cake, 4 said they liked the beer fermented with a direct pitch of fresh yeast, 2 had no preference despite noticing a difference, and 1 person reported perceiving no difference between the beers.

My Impressions: Out of the 5 semi-blind triangle tests I attempted, I correctly identified the odd-beer-out every time based purely on aroma. To me, the beer fermented with the yeast cake had a thinner mouthfeel and slightly odd aroma that was absent in the batch fermented with a direct pitch of fresh yeast, which I preferred.

| DISCUSSION |

As the microorganism responsible for converting the sweet wort brewers make into delicious beer, it makes sense that yeast should be treated with care, and ensuring adequate viability is one way to do that. While widely viewed as being less of a problem than underpitching, overpitching yeast is associated with certain less desirable characteristics including thin body and a yeasty flavor. Corroborating these claims, tasters in this xBmt were indeed able to reliably distinguish a Vienna Lager fermented with the yeast cake from a previous batch from one fermented with a direct pitch of fresh yeast.

While most brewers are less concerned with overpitching than underpitching, these results align with those from a couple past xBmts on the same variable, suggesting it may be worth more attention than some give it. It’s possible beer style is a factor, as differences tend to be easier to detect in more delicate lagers, though the feedback provided by some tasters following completion of the triangle test support claims about overpitching. Interestingly, taster preference was evenly split between the batches, which is further evidence of the subjectivity of preference.

I direct pitch fresh yeast for the majority of beers I brew, though I’ve certainly reused yeast in the past and have found success pitching around 200 mL slurry into fresh wort. Admittedly, I wasn’t convinced fermenting on an entire yeast would be much different than fermenting with fresh yeast, so I was a bit surprised with both the blind taster data as well as my own ability to tell these beers apart. Given my personal distaste for the characteristics in the beer fermented on the yeast, I’ll definitely be sticking to pitching smaller volumes of yeast slurry when not using fresh yeast in the future.

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

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