Author: Phil Rusher

One of the most important factors when it comes to making consistently high quality beer is yeast health, which includes two primary components, one being viability. Viability refers to the number of living cells in a given population of yeast, and it’s what brewers focused on pitch rates are largely concerned with. The most popular method for ensuring good viability involves making a yeast starter a couple days before brewing, allowing the yeast to go through the log phase where cell multiplication occurs. As yeast ages, cells die and thus viability is reduced, hence the recommendation to use yeast as fresh as possible.

The other component of yeast health is vitality, which has nothing to do with cell counts, but rather is an indicator of yeasts metabolic activity. To put it simply, vitality is a measure of yeasts readiness to ferment. One way to ensure high yeast vitality is to use what’s come to be known as a vitality starter, which involves pitching yeast into a relatively small amount of wort and allowing it spin on a stir plate for approximately 4 hours prior to pitching.

There’s no denying that both viability and vitality are important, and that the best results will be had when both are high. With past xBmts suggesting beers pitched with yeast of high vitality can be of similar quality as beers fermented with highly viable yeast, I began to wonder about the role yeast freshness plays and designed an xBmt to test it out!

| PURPOSE |

To evaluate the differences between a beer fermented with fresh yeast and the same beer fermented with old yeast when vitality starters are used.

| METHODS |

I went with a relatively simple Pale Ale for this xBmt and opted to use a yeast strain said to be somewhat characterful though still appropriate for American styles.

Overton

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 44.9 IBUs 6.9 SRM 1.057 1.013 5.8 % Actuals 1.057 1.01 6.2 % Fermentables Name Amount % Mecca Grade Lamonta: Pale American Barley Malt 8 lbs 72.73 Mecca Grade Metolius: Munich-style Barley Malt 1.75 lbs 15.91 Mecca Grade Rimrock Vienna-style Rye Malt 1 lbs 9.09 Mecca Grade Opal 44: Toasted Toffee Barley Malt 4 oz 2.27 Hops Name Amount Time Use Form Alpha % Hallertau Magnum 14 g 60 min Boil Pellet 11 Equinox (HBC 366) 10 g 20 min Boil Pellet 12.9 Loral 10 g 20 min Boil Pellet 10.5 Equinox (HBC 366) 14 g 10 min Boil Pellet 12.9 Loral 14 g 10 min Boil Pellet 10.5 Yeast Name Lab Attenuation Temperature Joystick (A18) Imperial Yeast 75% 60°F - 70°F Notes Water Profile: Ca 156 | Mg 0 | Na 25 | SO4 156 | Cl 63 Download Download this recipe's BeerXML file

In September 2018, I received a pouch of Imperial Yeast A18 Joystick that was manufactured on August 8, 2018 and stowed it away in my refrigerator; in April 2019, I received another pouch of the same yeast that was manufactured on March 19, 2019. By brew day the first week of May, the yeasts were 9 months and 2 months old, respectively, for an age difference of approximately 7 months.

A few days prior to brewing, I collected the proper volume of RO water.

After adjusting the water with minerals to my desired water profile, I hit the flame to heat it up then proceeded to weigh out and mill the grain.

With the water sufficiently heated, I added the crushed grain then checked to ensure it hit my target mash temperature.

During the mash, I prepared the kettle hop additions.

When the 60 minute mash rest was complete, I collected the sweet wort in my boil kettle.

I placed the filled kettle on my burner, lit the flame, and tossed in the first wort hop addition. The wort was then boiled for 60 minutes with hops added as stated in the recipe.

At the end of the boil, I chilled the wort then took a refractometer reading indicating my target OG was hit.

Next, identical volumes of wort were racked to Brew Buckets.

At this point, I transferred 500 mL of wort from each batch to separate sanitized flasks, pitched the old yeast into one and the fresh yeast into the other, then placed them on stir plates.

The wort was then placed in my chamber and allowed to chill for 4 hours while the starters spun, after which they were both at my desired fermentation temperature of 65°F/18°C. The vitality starters were pitched. I noticed airlock activity from the fresh yeast batch after just 6 hours, though the batch pitched with old yeast was showing signs of activity just 12 hours after pitching. After 5 days, it appeared fermentation had finished for both beers, so I began taking hydrometer measurements that indicated the beer fermented with fresh yeast finished 0.001 SG point lower than the one fermented with old yeast.

The beers were transferred to sanitized kegs and burst carbonated in my keezer. I opted against fining with gelatin in order to demonstrate any impact yeast age has on clarity. Following 2 weeks of cold conditioning, the beers were ready to serve to participants.

| RESULTS |

A total of 47 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the beer pitched with a vitality starter of fresh yeast and 2 samples of the beer pitched with a vitality starter of old yeast in different colored opaque cups then asked to identify the unique sample. While 22 tasters (p<0.05) would have had to identify the unique sample in order to reach statistical significance, only 18 (p=0.28) made the accurate selection, indicating participants in this xBmt could not reliably distinguish a Pale Ale fermented with 9 month old yeast from one fermented with 2 month old yeast when vitality starters were used.

My Impressions: Out of the 7 triangle tests I attempted, I chose the odd-beer-out 6 times. While both beers tasted good and shared similar malt flavors, I perceived a bright hop character and mild fruity esters in the beer fermented with fresh yeast while the hops were slightly muted and the ester character was stronger in the version made with older yeast.

| DISCUSSION |

A ubiquitous adage among brewers is that brewers make wort and yeast make beer, which is technically accurate, as yeast transforms the sugars in wort into ethanol, carbon dioxide, and other compounds. To that end, it’s fair to say yeast deserves close consideration when producing beer, ensuring it has the requisite health to perform its job right. Viability has long been a concern of the yeast conscious, but the idea of improving vitality only recently seems to have gained some popularity, with brewers spinning up relatively small starters that get pitched just a few hours later. The fact tasters in this xBmt were unable to tell apart beers fermented with either 9 month old or 2 month old yeast when a vitality starter was used for both suggests increased vitality may help to compensate for a lack in viability.

These results seem promising on the surface, particularly for those who may have waited a bit too long to use a pitch of yeast. Indeed, there are many anecdotal reports from brewers who say that improving yeast vitality led to positive outcomes, which the findings from this xBmt support. However, there were some objectively measurable differences between the batches, such as the increased lag time in the batch pitched with old yeast. Additionally, the beer fermented with fresh yeast was noticeably clearer, something that may or may not matter depending on personal preferences.

I’m not sure whether it was bias, a sensitivity to something others didn’t perceive, or a mix of both, but I felt the beers in this xBmt were perceptibly different. Thankfully, neither tasted bad, but given how similar I treated both, I’m compelled to believe the differences I perceived were more likely a function of yeast health than something else. I’ve used vitality starters numerous times, they’re a great tool that allow brewers to quickly and easily improve yeast health. That said, if I’m concerned about a pouch of yeast that’s a bit too old, I won’t hesitate to propagate in a standard starter to improve viability.

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

Support Brülosophy In Style!

All designs are available in various colors and sizes on Amazon!

Follow Brülosophy on:

If you enjoy this stuff and feel compelled to support Brulosophy.com, please check out the Support page for details on how you can very easily do so. Thanks!

Advertisements

Share this: Facebook

Twitter

Pinterest

Tumblr

Email



Like this: Like Loading...