3

My idea is that instead of using pure oxygen to reach higher DO levels (fx 12ppm) one could use aeration that will only reach 8ppm. But since the purpose is to give the yeast access to enough oxygen that it will use for reproduction the yeast will consume the oxygen in the wort and if we by aeration keeps the DO level there would be the same amount of oxygen available to the yeast eventually.

Is this an feasible approach? And if so how long should one aerate in order to get the benefits of higher DO levels?

3

Yes, it definitely should be a feasible method.

Yeast will rapidly (within a matter of hours) consume the oxygen that has been provided, at which point you may provide it more and it will happily accept. The important point in determining the quality of the subsequent fermentation, as you suggest, should be how much oxygen the yeast consumes in total.

There are a few practicalities, however, that may make doing this accurately somewhat difficult:

  • How you provide aeration can matter a lot. I used to do this by shaking a full carboy. The initial aeration is not so difficult, but once fermentation gets going (which ideally will be very rapidly) carbon dioxide will almost immediate begin to saturate the wort. This means that, if you go to shake to aerate more several hours later (say somewhere between 2-12), you can potentially have a gushing mess on your hands. Even if you are using an air pump with a stone, this may cause violent foaming.

  • Unless you have a dissolved oxygen meter, you won't have any way of knowing how much oxygen remains unused by the yeast when you add more. So you won't have any good way of determining how much oxygen in total has been added. In general, this should be fine since over-oxygenation isn't a huge concern in home-brewing and it's typically better for us to ere on the side of caution (more oxygen, rather than less). It will just become a matter of trial-and-error to see what works best for your particular fermentation techniques.

  • Experiments have suggested that the optimum time to oxygenate your wort is actually a number of hours after yeast pitching. These experiments also suggest that when added at the optimal time, the amount of oxygen needed may be as little as half that needed when adding right at yeast pitching (i.e. if you used 16 ppm at pitching you may only need 8 ppm added at 4 hours to achieve an identical fermentation). This is most likely due to the yeast membranes becoming increasingly functional as they move out of the 'hibernation' (or stationary) phase into active fermentation, and so becoming better able to utilize any given amount of oxygen as time progresses (up to a point). So you may see how this effect could lead to difficulty accurately matching the amount of oxygen added to the amount needed by the yeast when adding over a period of time.

'[H]ow long should one aerate in order to get the benefits of higher DO levels?'

I would actually suggest doing oxygen addition in 'batches', or discrete additions, several hours apart, rather than as one continuous addition. If you have a method you're fairly confident is saturating your wort (i.e. to ~8 ppm oxygen) start with that, then repeat that maybe 4 hours later. I would play around quite a bit too (try it at 2, 4, 6 hours &c; try it for half or a quarter of the initial time; stuff like that). Every yeast strain has its own particular needs for oxygen, and will react differently to receiving more oxygen some time after the initial dose (in any given wort, no less) so saying just how much you need to oxygenate and when is basically impossible.

| improve this answer | |
2

The other solution is to pitch enough yeast to make aeration unneeded or at least less necessary. That's what I do.

| improve this answer | |
  • That seems a much more sensible approach to the problem. IMHO unnatural aeration seems as desperate as using olive oil.What is this love/hate relationship some brewers have with oxygen? – barking.pete Aug 18 '17 at 16:08
  • they uncritically believe everything they've been told without studying the science behind it or doing their own testing. Olive oil is a prime example. When I contacted Grady Hull, who wrote the thesis about olive oil, he was astounded that homebrewers took it like they did. He had no intention of olive oil being used to replace aeration. It was a technique for yeast storage, not propagation. And even then it didn't work well. – Denny Conn Aug 19 '17 at 16:04
  • 'He had no intention of olive oil being used to replace aeration.' Perhaps, but that is exactly what the paper was about. In his words, the study was 'conducted to evaluate [...] beer, which had been fermented with yeast that was treated with olive oil during storage instead of aerating the wort'. The author later states: 'This project set out to investigate the effects of using olive oil addition to storage yeast vs. traditional wort aeration'. I.e. the effects of replacing one technique with another were studied. – Franklin P Combs Sep 5 '17 at 12:04
  • @barking.pete This is a situation where home-brewing differs significantly from commercial brewing. On this scale we can easily afford to pitch five times the yeast, to eliminate the need for yeast growth. On a large scale, that becomes cost-prohibitive. Even to achieve standard pitching rates requires costly propagation equipment or lab-grown pitchable slurries. These costs are therefore defrayed by re-pitching the yeast for multiple generations, and this is impossible to do for the typical 10-15 generations without allowing yeast growth during each generation, to generate fresh yeast. – Franklin P Combs Sep 5 '17 at 12:15
  • (cont.) Oxygen (or some suitable replacement) is what allows for yeast growth and multiple generations of re-pitching. If every batch were pitched with the full (terminal) cell count you would essentially have the same yeast cells (i.e. the oldest) fermenting the last batch as the first batch, which would make for highly unpredictable behavior. Also, some important flavor attributes (mainly esters) are specifically related to yeast growth and pitching enough to preclude growth may reduce their levels to undesirable quantities. But, it's still a fine idea for the small scale. – Franklin P Combs Sep 5 '17 at 12:22
1

I think the aeration method outlined would work by making a lower but more prolonged level of O2 available - but it might be over elaborate or even unnecessary.

The need for oxygen during fermentation is not continuous. As noted, the yeast only needs it to grow. It is not needed to metabolise sugar to alcohol/CO2. So once the required yeast population is present there is no further need for oxygen. One might preclude any oxygen being needed at all by simply pitching a sufficient and full amount of hydrated active yeast into the wort.

The oxygen is used to make sterols required for the yeast cell wall. It seems that olive oil (in very small amounts) can also be used for this purpose, precluding the need for any oxygenation at all.

| improve this answer | |
  • 2
    I find the use of olive oil questionable. First AFAIK yeast cannot hydrolyse the fat, so it won't have access to the bound fatty acids. Second I'm not sure it can synthesize sterols from fatty acids alone. Third the results in the paper by Hull shows sign of inadequate oxygenation (more esters). Fourth tests using no areation in the control batch shows no percievable differences. – skyking Aug 15 '17 at 5:22
  • In addition providing the full amount of yeast is probably not feasible. Recommended pitching rates is more than an order of magnitude less than the full amount. With reasonable pitching rate the yeast need to grow anyway. – skyking Aug 15 '17 at 5:34
  • To be clear the proposed method is to use air to aerate and use that for a longer time instead of pure oxygen. Not to continue aeration indefinitely and after the growth phase has completed. What's over elaborate? That's for each brewer to decide. But we're talking having a pump pumping air into the wort or having a O2-tube and flow regulator pushing O2 into the wort - not that huge difference to objectively say which is more elaborate. – skyking Aug 15 '17 at 5:38
  • I think skyking should re-read the paper. Essentially olive oil and aeration (not the lack of it) gave very similar results within style parameters of the test brew. it seems the brewery's own taste panel preferred the olive oil variety to the standard brew. The test brew was even released to the public as "standard product" without adverse comment.. So using olive oil seems to be a viable if somewhat odd method. It is also quite a viable idea to pitch yeast at a much higher rate than recommended. One can add it to or grow it in the brew with little real difference in outcome. – barking.pete Aug 15 '17 at 11:22
  • 1
    @barking.pete Yes it was significant, it was consistently evaluated as having higher levels of esters, it was consistently measured as having higher levels of esters (and not just a little bit - in some cases it was a factor two or more). As far as I can see there were no measurement of the yeast mass - so I don't see where you get that conclusion from. – skyking Aug 22 '17 at 5:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.