Here's a common dilemma that many pro brewers come to us with:
"I have to brew several times to fill my fermentors, but there isn't much good advice out there. How much yeast do I pitch? Which batches of wort should be oxygenated? Is it better to get the tank full in one day or can I wait a day or two between brews?"
Ultimately, you (the brewer) are looking for best practices for how to get lots of beer out the door while minimizing yeast stress and ensuring batch-to-batch consistency. And we are here to help make all the cool science accessible to you.
Our general advice
There are more details below if you are interested, but here are the basics:
- Pitch the yeast and oxygenate the wort on the first fill. Pitching the yeast early will ensure yeast growth begins. Oxygenating the wort also ensures the yeast will grow. Do not leave wort sitting without yeast for too long.
- Pitch enough yeast for the first 24 hours. For example, if you are brewing 2x10hL on one day then 2x10hL on day two, pitch 20hL worth of yeast.
- Oxygenate every fill on the first day. You shouldn't worry about oxidation as long as the yeast is still active and being given new food. This gets a bit more complex when you're hitting 3+ fills (in this case, you don't need to oxygenate the last one).
I'm not sharing much original research from Escarpment in this post, because a lot of it has been done already! Luckily for us, there has been a lot of attention paid to the subject of wort aeration, and even multi-fill fermentations over the years. We have the Master Brewers Association of the Americas (MBAA) and the American Society of Brewing Chemists (ASBC) to thank for publishing this info, as well as the glory years of beer research, where large breweries did not hoard trade secrets and published their research openly. There is an enormous wealth of beer knowledge in the MBAA and ASBC's archives. And luckily for you, most of the research from 50 years ago is still very relevant today!
1. Pitch the yeast and oxygenate the wort on the first fill
Pitching the yeast early will ensure yeast growth begins, ultimately meaning your fermentations will also finish sooner. Oxygenating the wort on the first fill also ensures the yeast will grow, since oxygen is required for optimal yeast growth. Remember: you aerate to provide oxygen for your yeast, not to oxidize your wort!
Oxygen is taken up quickly (~2-3 hours) by yeast in a wort fermentation. Figure from Kucharczyk and Tuszyński (2017).
Do not leave wort sitting without yeast for too long. The surprising reason for this is that a number of compounds in the wort itself can oxidize in the span of hours, including compounds extracted from your malt and hops. This was first suggested to us in a fantastic ASBC Fishbone Diagram (ASBC Fishbone IIb; Casey; Process Control for Yeast Viability & Vitality) which leads to interesting research by Kirsop in the 1970s on wort oxygenation. Kirsop showed that, after a few hours, unpitched and oxygenated wort contained no measurable dissolved oxygen. This means that oxygenating wort and letting it sit for hours before pitching yeast is essentially a waste of oxygen and might have downstream effects on flavour stability.
2. Pitch enough yeast for the first 24 hours
For example, if you are brewing 2x10hL on one day then 2x10hL on day two (40hL total), pitch 20hL worth of yeast (at your target pitching rate).
The reason for this is that you want to make sure you are pitching an adequate pitch rate for the first batches of wort to start fermentation since under-pitching can lead to undesirable flavour or consistency outcomes. The reason to not pitch enough yeast for the entire fermentor volume is that this is technically an over-pitch on the first day, and the yeast will not go through an optimal number of cell divisions, potentially leading to issues with repitching as well as muted flavours.
By the second day/after 24 hours, the beer should be actively fermenting and the yeast will have completed most of its cell divisions/growth, so you likely will not see any benefit from pitching additional yeast on the second day. The same holds true if you've got a 48 hour (or two-day) gap between brews.
3. Oxygenate every fill on the first day
You shouldn't worry about oxidation as long as the yeast is still active and being given new food. In our experience, actively growing or fermenting yeast will consume most of the dissolved oxygen quite quickly, on the scale of minutes to hours. Even in propagation, where air is constantly added, we found that yeast can consume all the oxygen thrown at it once there are enough cells!
Some surprising results from an in-house yeast propagation - even in continuously aerated wort, a growing yeast culture can consume a lot of the dissolved oxygen thrown at it!
This gets a bit more complex when you're hitting 3+ fills (in this case, you typically don't need to oxygenate the last one). Late oxygen addition beyond 24 hours after pitching does not appear to promote faster fermentation. However, oxygenating a ferment at 12 hours does increase fermentation rate and attenuation, which supports this practice being applied to very high gravity ferments like imperial stouts and barleywines.
A study in 1997 by Yokoyama and Ingledew extended Kirsop's work by looking specifically at different multi-fill strategies using miniature fermentations. This is a really cool study! While there are many details, the outcome was that pitching enough yeast for all the brews in the first 24 hours is ideal for fermentation performance. They also showed that the best performance in a 4-fill fermentation came from oxygenating the first 3 fills and not oxygenating the 4th fill.
CaveatsMost studies performed on the relationship between yeast, wort oxygenation, and filling have been performed with lager yeast (Saccharomyces pastorianus). We know that ale strains (S. cerevisiae) are more genetically diverse, and also have a wider spectrum of oxygen requirement. So there remains a bit of a knowledge gap in how to dial in ideal oxygenation, multi-fills, and yeast health with ale yeasts which are more commonly used for craft beer production.
Kirsop, B. H. (1974). Oxygen in Brewery Fermentation. Journal of the Institute of Brewing, 80(3), 252–259. https://doi.org/10.1002/j.2050-0416.1974.tb03614.x
David, M. H., & Kirsop, B. H. (1973). Yeast Growth in Relation To the Dissolved Oxygen and Sterol Content of Wort. Journal of the Institute of Brewing, 79(1), 20–25. https://doi.org/10.1002/j.2050-0416.1973.tb03491.x
O’Connor-Cox, E. S. C., & Ingledew, W. M. (1990). Effect of the Timing of Oxygenation on Very High Gravity Brewing Fermentations. Journal of the American Society of Brewing Chemists, 48(1), 26–32. https://doi.org/10.1094/asbcj-48-0026
Yokoyama, A., & Ingledew, W. (1997). The effect of filling procedures on multi-fill fermentations. Technical Quarterly, 34(1), 320–327.
Kucharczyk, K., & Tuszyński, T. (2017). The effect of wort aeration on fermentation, maturation and volatile components of beer produced on an industrial scale. Journal of the Institute of Brewing, 123(1), 31–38. https://doi.org/10.1002/jib.392