What is the experiment?
To determine what flavour impacts yeast has on a final product under these 4 conditions:
- When fresh yeast and priming solution is used post filtration
- When fresh yeast and priming solution is used pre-filtration
- When yeast in suspension and priming solution is used pre-filtration
- When product is force carbonated via brite tank
What product was used and how was it collected, packaged and handled?
The product used was the NCTB Butler’s Bitter, which is a Best Bitter. This product was chosen because it is regularly produced at the brewery and fairly consistent. Samples were collected by placing tees before and after the filter such that the keg manifold could be used to pull samples.
The flat product was placed in cold storage until the necessary ingredients could be prepared for packaging day. A neutral lager yeast (Fermentis S-23) was used for dosing at a rate of 0.1 • 106 cells / mL as per a guide from Northern Brewer. A priming solution was prepared using formulae within the Priming section of the MBAAs Handbook of Basic Brewing Calulations (Holle, 2010, pp 69 – 73).
Product was filled via Beer Gun into six 355mL bottles per experiment type, with the appropriate amount of priming solution and yeast slurry. Slurry was prepared by rehydrating yeast into distilled water for 20 minutes followed by a cell count. The product was not filled under pressure.
Experiment was then placed within the mechanical room of the teaching brewery for approximately four weeks to simulate 2 – 4 months of product aging. The goal was to accelerate oxidation and encourage yeast death.
How was the tasting panel performed?
Tasting was performed where anchors were scored privately by the experiment team and then given to the panel along with 5 other samples. To verify the panels calibration, we served our anchors along with the beers we were testing. Our panel consisted of 13 fellow students who have been focusing on sensory analysis of beer for the last 14 months.
The flight was delivered as follows:
- Anchor 1 – Counter Pressure Filled (different production run)
- Anchor 2 – Beer Gun Filled
- Sample 1 – Unfiltered w/Yeast & Sugar
- Sample 2 – Filtered w/Yeast & Sugar
- Sample 3 – Counter Pressure Filled (Anchor 1)
- Sample 4 – Unfiltered w/Sugar
- Sample 5 – Beer Gun Filled (Anchor 1)
Analysis of Results
We can see that our panel wasn’t perfectly calibrated and missed the mark on a few of the sensory components of the product we served them. However, something of interest is how the versions that were dosed with fresh yeast seemed to help protect the product from some off flavours associated with oxidation.
These beers performed a bit better than the counter pressure filled bottles in terms of papery notes, and appeared to be a bit more floral as well. However, these were also two separate batches of beer, so we cannot for sure know that it wasn’t the extra hop additions which are responsible for this. Though, if we compare the floral notes of the re-yeasted beers with the Brite beer packaged via beer gun (same batch of beer) it seems to have had an impact.
Something that is also somewhat interesting is how the beer that was packaged with whatever yeast was left in solution performed worse. The beer had been cold crashed before running through the filter, so there is a good chance that there weren’t enough cells in solution or they weren’t able to take up as much oxygen as the freshly yeasted samples.
While not entirely conclusive, adding fresh yeast before packaging might be an option to help improve shelf life of a product. For people in the competition scene, this could be very helpful in decreasing the risks of products oxidizing during storage or shipping.
The additional information regarding the bottle conditioned beer that was served without yeast means that it should be possible to try and replicate this test at a homebrew level. The amount of equipment needed to replicate the test should be fairly minimal with the most expensive components being a hemocytometer and microscope to help control yeast dosing rates. The other other pieces of required equipment are 1mL pipettes and a pipette pump.