Let's get Particular
Let's get Particular
Should we use encapsulated yeast when we brew our beer?
Dear brew enthusiasts,
In this weeks episode, I will be talking about the use of immobilised yeast for brewing beer. The vast majority of brewers use a batch brewing approach, In which yeast is used to ferment a single batch of beer. Immobilising your yeast in some way ensures that you can continuously exchange the beer you have produced with new wort, without having to interrupt your fermentation and disturbing your yeast.
The question, of course, is there a difference in quality and perception when you compare beers produced by either method. The paper by Benucci et al. (2021) that I am about to discuss is all about this question.
The authors sought to investigate the impact of encapsulating a commercial yeast strain into particles made of chitosan-calcium alginate. This compound can form a porous matrix around clusters of yeast cells, allowing the exchange of nutrients, metabolites, gas, and alcohol but block the spread of yeast into the wort. The authors managed to effectively encapsulate the vast majority of yeast clusters (>93%) and use the yeast for fermentation.
To test whether encapsulation had any impact, the authors added free yeast and encapsulated yeast cultures to batches of a pale ale wort, followed by a primary fermentation step. Finished green beer (defined as beer for which the gravity is constant for at least four days at the end of primary fermentation) was conditioned in bottles and used for analyses.
The authors used a robust set of parameters to measure yeast performance:
Specific gravity
Dissolved oxygen
pH and total acidity
Yeast assimilable nitrogen (YAN) (the total of nitrogen that is available to yeast for growth)
Alcohol
Colour
CO2
Bitterness
Chill haze
Volatile profile
Sensory analysis
What did they find?
The results of their experiments and analyses were fascinating. Firstly, the authors observed that encapsulated yeast needs longer to finish the fermentation. Free yeast fermentation took seven days, whereas the authors ended fermentation with encapsulated yeast after 13 days. These results mean that free yeast performs best as far as time is concerned (or fermentation rates).
Not surprisingly, specific gravity, pH, alcohol content, colour and bitterness were not significantly different between methods. Let yeast finish fermentation (irrespective of the time it takes) will ensure that alcohol levels and the specific gravity readings are similar.
Where it becomes interesting is where the authors observed differences. I will summarise these results below.
Chill haze. As you can imagine, encapsulating yeast cells confines all the materials into particles that you can easily separate from your beer. It is also likely, that lysis of your yeast (which results in the release of cell debris into your wort) has less impact. While yeast may still lyse within the particles (perhaps there is even more lysis), debris will not get into the beer very quickly. As the haze in beers comes, for the most part, from proteins interacting with polyphenols in your beer, you can see how the use of encapsulated yeast can decrease beer haziness.
Volatiles. While I list the volatiles as one parameter that changes as a function of the method, I do not wish to overstate the importance of this result. Per definition, any beer carries a very complex volatile cocktail of thousands of compounds. While the authors found some differences for some of the compounds they analysed, levels did not change for most analytes. It is also unclear whether the differences were the direct result of yeast encapsulation or the difference in fermentation time used between methods.
The authors found that beer fermented by encapsulated yeast had higher levels of benzaldehyde, acetophenone, ethyl butyrate and isoamyl alcohol. These compounds are thought to give beer honey and caramel-like odours and spicy notes. These volatiles are also associated with fruity flavour.
Beer produced with free yeast contained higher levels of linalool, esters, and alcohols when compared to beer made with encapsulated yeast. The observed increase in complexity of the aromatic profile resulted in yeasty, flowery and hoppy notes.
Sensory analyses, in essence, confirmed the results obtained through volatile profiling. The figure here shows this quite nicely.
What does this all mean?
Simply put, continuous fermentation is an avenue to explore if brewers wish to switch their operations to constant fermentation. A switchover comes with significant caveats. Firstly, fermentation times may increase. The authors extended fermentation time for the encapsulated. This study suggests that yeast becomes less efficient or slower fermenters. It is possible that using another matrix (that makes the capsules) and other yeas strains better suited for encapsulated goes a long way in addressing this issue. We should take note, however, that the authors used a batch-brewing setup for their comparisons. It is nearly impossible to predict what will happen if you do the same experiment with a continuous flow system.
Secondly, as the profile of your beer will be different, recipes will have to be modified. To what extent this allows you to replicate the profile of a batch-brewed beer needs to be determined.
I hope you enjoyed this weeks post from The Beerologist. Have a great weekend!
Best wishes,
Edgar @ The Beerologist.