Timeline of Beer Yeast Ester Production
When are esters produced by yeast in my beer fermentation?
Ester formation primarily occurs during the active fermentation phase, which typically begins within the first 24-48 hours after pitching yeast[1][2]. However, the exact timing and rate of ester production can vary depending on several factors, including yeast strain, fermentation temperature, and wort composition (e.g. FAN).
Many studies have shown that the majority of ester production occurs during the exponential growth phase of yeast, which usually takes place within the first 1-4 days of fermentation [3][6]. During this period, yeast cells are rapidly multiplying and consuming sugars, leading to the formation of various flavor compounds, including esters. The conventional wisdom dictates that esters are mostly produced at the start of fermentation.
Is there any conflicting research? What about pressure fermentation?
Some research suggests that ester production follows a specific pattern throughout fermentation. A 2001 study described a three-phase timetable for ester production: 1) alcohol accumulates alone, 2) both alcohol and esters accumulate, and 3) esters accumulates alone [7]. In pressurized fermentations, it appears that ester accumulation reaches its maximum much later in the process, closer to 80% fermentation completion.
Do esters get formed during bottle conditioning, secondary aging, or dry hopping?
It's important to note that while most ester production occurs during active fermentation, some ester formation and modification can continue during the stationary and conditioning phases [6]. This is particularly relevant for certain yeast strains, such as those used in Belgian-style beers, which are known for their continued ester production during extended fermentation periods such as bottle conditioning. In pressure fermentation, ester production seems to be both reduced but also delayed until later in fermentation [7]. It is known that CO2 can inhibit the formation of esters through repressing expression of ester producing genes such as ATF1 [9].
Factors such as fermentation temperature, oxygen levels, and pitching rate can significantly influence the timing and quantity of ester production [4][5]. Higher fermentation temperatures generally lead to increased ester production, while higher oxygen levels at the start of fermentation can reduce ester formation.
An additional consideration is that esters can also be released through biotransformation. For example, hops contain glycosidically bound esters which can be freed through yeast biotransformation or through directly adding beta-glucosidase enzyme. Dry hopping can add an abundance of glycosidically bound esters, as well as "hop creep" enzymes creating glucose in the wort, which could enhance acetate ester formation (e.g. isoamyl acetate/banana, isobutyl acetate/bubblegum) later in fermentation.
How can I predict and control esters in my beer?
First, you can use additional Escarpment Labs resources such as "Decoding Ester Production in Beer Fermentation".
Brewers should seek out supplier data and insight on specific yeast strains and fermentation conditions when attempting to control or predict ester production in their beers.
More information and data on ester production by Escarpment Labs strains including the influence of temperature can be found in our Guide to Yeast Flavour and Biotransformation.
Citations:
[1] Verstrepen, K. J., et al. (2003). Flavor-active esters: Adding fruitiness to beer. Journal of Bioscience and Bioengineering, 96(2), 110-118.
[2] Pires, E. J., et al. (2014). Yeast: the soul of beer's aroma—a review of flavour-active esters and higher alcohols produced by the brewing yeast. Applied Microbiology and Biotechnology, 98(5), 1937-1949.
[3] Boulton, C., & Quain, D. (2001). Brewing yeast and fermentation. John Wiley & Sons.
[4] Saerens, S. M., et al. (2008). Parameters affecting ethyl ester production by Saccharomyces cerevisiae during fermentation. Applied and Environmental Microbiology, 74(2), 454-461.
[5] Peddie, H. A. B. (1990). Ester formation in brewery fermentations. Journal of the Institute of Brewing, 96(5), 327-331.
[6] White, C., & Zainasheff, J. (2010). Yeast: The practical guide to beer fermentation. Brewers Publications.
[7] Landaud, S., et al. (2001). Top pressure and temperature control the fusel alcohol/ester ratio through yeast growth in beer fermentation. Journal of the Institute of Brewing, 107(2), 107-117.
[8] Dufour, J. P., et al. (2003). Ester synthesis during fermentation: enzyme or chemical catalysis? Brewing Science, 56(3-4), 41-46.
[9] Souffriau B. et al. (2022). Polygenic Analysis of Tolerance to Carbon Dioxide Inhibition of Isoamyl Acetate “Banana” Flavor Production in Yeast Reveals MDS3 as Major Causative Gene. Applied and Environmental Microbiology, 88(18): e00814-22.
[10] Svedlund A. et al. (2022). Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation. Applied and Environmental Microbiology, 106(13-16):4929-4944.
Additional links:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836583/
https://draymans.com/ester-production-in-yeast/
https://escarpmentlabs.com/blogs/resources/decoding-ester-production-in-yeast-fermentation
https://www.sourbeerblog.com/understanding-esterification/
https://www.micetcraft.com/fermentation-timeline/
https://byo.com/article/fermentation-time-line/
https://scottjanish.com/esters-and-fusel-alcohols/
https://www.homebrewtalk.com/threads/when-do-yeast-produce-esters.248452/