Author: Matt Del Fiacco

One of the first suggestions seasoned brewers offer when rookies ask for ways to improve their beer is to pitch the right amount of viable yeast. Starting with more viable yeast is believed to reduce yeast stress, leading to healthier fermentations and reducing the possibility for off-flavors in the finished product. One apparent exception to this rule has to do with the currently popular yeasts known as kveik, which purportedly produces the most desirable characteristics when pitched at very low rates.

A recent poster presentation at the MBAA conference titled The Impact of Pitch Rate on Kveik Ferments, by Richard Preiss and Iz Netto of Escarpment Laboratories, provided some data-based context for this longstanding folk guideline. It concluded that lower kveik pitch rates resulted in a slower fermentation than higher pitch rates, but terminal gravity was ultimately very similar. Additionally, the study found that the impact of pitch rate on finished beer characteristics varied between different types of kveik.

When results from a recent xBmt showed beers fermented with a Voss kveik variant at drastically different temperatures were largely indistinguishable, a number of readers suggested this was likely due to the fact both were pitched at the same rate, which was much higher than is traditionally suggested. Intrigued both by the idea that a lower pitch rate could lead to a more desirable outcome as well as Preiss and Netto’s conclusions, I decided to test it out for myself.

| PURPOSE |

To evaluate the differences between beers fermented with the Voss kveik strain where each received a different pitch rate.

| METHODS |

For this xBmt, I opted to go with a recipe similar to the one brewed for the recent kveik fermentation temperature xBmt.

Redundancy

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5 gal 90 min 24.1 IBUs 3.6 SRM 1.062 1.015 6.3 % Actuals 1.062 1.015 6.2 % Fermentables Name Amount % Pilsner (2 row) (Gambrinus) 11.75 lbs 100 Hops Name Amount Time Use Form Alpha % Magnum 10 g 90 min First Wort Pellet 12 Czech Saaz 26 g 15 min Boil Pellet 3.5 Yeast Name Lab Attenuation Temperature Loki Imperial Yeast 79% 68°F - 98°F Notes Water Profile: Ca 54 | Mg 11 | Na 25 | SO4 81 | Cl 65

Download Download this recipe's BeerXML file

After collecting two identical volumes of water on brew day, I turned on the elements to heat them up.

I then weighed out and milled the grain for each batch.

With the water adequately heated, I incorporated the grains then checked to make sure each batch was at the same mash temperature.

During the mash rest, I weighed out the kettle hop additions.

When each 60 minute mash was complete, I removed the grains and brought the worts to a boil.

When the 60 minute boils were finished, they were quickly chilled on their way to sanitized fermentation kegs.

A refractometer reading confirmed target OG was hit.

Prior to brewing the beers for this xBmt, I consulted with Larsblog’s Lars Marius Garshol who recommended a pitch rate of approximately 1 million cells per milliliter based on the target OG. I proceeded to weigh out the amount of yeast for both batches using two pouches of Imperial Yeast A43 Loki, a Voss variant.

I then proceeded to pitch the yeast, which amounted to pitch rates of approximately 18 billion and 220 billion cells for the under-pitch and standard pitch rate beers, respectively.

The fermentation kegs were then set next to each other chambers controlled to 96°F/36°C.

Unsurprisingly, the underpitch beer took a bit longer to show signs of activity than the one pitched with more yeast, but at 18 hours, both appeared to be fermenting similarly. Hydrometer measurements taken 2 weeks later showed both beers achieved a similar FG.

At this point, the beers were pressure transferred to sanitized serving kegs.

The filled kegs were placed in my cool keezer where they were burst carbonated and left to condition for a couple weeks before I served them to tasters.

| RESULTS |

A total of 21 people of varying levels of experience participated in this xBmt during a monthly Joliet Brewers Guild meeting. Each participant was served 1 sample of the standard pitch rate beer and 2 samples of the underpitched beer in different colored opaque cups then asked to identify the unique sample. At this sample size, 12 tasters (p<0.05) would have had to identify the unique sample in order to reach statistical significance, though only 9 (p=0.24) did, indicating participants in this xBmt were unable to reliably distinguish beers fermented with the Voss kveik variant pitched at either standard or low rates.

My Impressions: Out of the 10 semi-blind triangle tests I attempted, I identified the unique sample 7 times, which while not perfect, is decent odds. No doubt about it, the beers were way more similar than they were different, both leaning slightly sweet with a pleasant cracker malt character. However, to my palate, the underpitched beer had a very subtle apple character in both the aroma and the flavor that was absent in the standard pitch batch. Either way, I enjoyed both equally.

| DISCUSSION |

Kveik has had a huge impact on the brewing scene over the past couple years, and much of what we know about this unusual family of yeasts amounts to hearsay based on personal anecdote. One of the more common suggestions when it comes to using kveik is to underpitch, which is said to lead to the production of desirable characteristics. Interestingly, tasters in this xBmt were unable to reliably distinguish beers fermented with Imperial Yeast A43 Loki, a Voss isolate, at rates of either 18 billion cells or 220 billion cells, suggesting pitch rate may not have as much of an impact on beer character as many believe.

These results indicate one of two things—either both beers possessed the desired characteristics, or it was absent in both. This is an interesting layer to the Preiss and Netto’s research showing different pitch rates did lead to noticeable chemical differences when using Voss kveik. One possible explanation for this is that Preiss and Netto fermented their beers at 68°F/20°C compared to the 96°F/36°C temperature in this xBmt. Moreover, the Voss isolate used in this xBmt came from a different lab than that of Preiss and Netto’s, so there’s a chance this may have contributed to the disparate findings.

While these results call into question claims that underpitching kveik leads to the production of unique characteristics, it also indicates fairly small amounts can be used without producing off-flavors, which is definitely a positive. There remains much to learn about kveik usage, but given these results and my own personal experience with the beers, I’ll definitely be getting a bit more mileage out of each pouch I use 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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