Aeration via Continuous Stirring or Air Pump?

[Lost Tyger]

So, I utilized the standard drill stirrer on my first couple batches of mead (still ageing), and I wasn't happy with the foam formation from the dissolved CO2. Maybe I'm too impatient, but I figure there's gotta be a better way.

In reading around here, I saw that somebody had tried a continuous fermentation on a stir plate, and I've gotten my head around the electronics enough that I think I could make one suitable for a 5 gallon glass carboy with some lumber and ~$5 of parts. With an 'open' fermentation, with a sanitized cloth over the carboy neck, this would allow for continuous aeration during the first 1/3 of fermentation by the same sort of mechanism that the drill stirrer uses, just continuously.

However, a friend suggested that I could just as easily get an aquarium pump and aeration stone and pump air into the carboy through the stone continuously over the first 1/3 of fermentation. Wouldn't get the same stirring action, but it would be a very efficient way of dissolving air in the mead.

I'm interested in trying both, as they will both likley prevent all that foaming problem that I had with my first few, but I thought I would solicit some thoughts from the experts on these techniques. Anyone see anything wrong with either of these, in particular?

 

[Braxton]

I'm glad that you're taking an interest in the stir plate method, I would really like to hear what other people think about it. I'm doing more experiments with it currently to see if I can duplicate the results, and what the limitations of it are.

They actually do make carboy sized stir plates for use in scientific settings, I know some homebrewers out there have snagged used ones but I think they are very expensive new. I've got no advice on building your own, unfortunately, but I think that it would work well.

There is such a thing as too much oxygenation, but the things that I've read about it are primarily related to beer brewing and discuss only the upfront dose of oxygen, not continuous adding of oxygen. If you're interested I can look up the details in Jamil's book on Yeast.

The last test I did with a stir plate involved doing what you are describing, I left it open for the first 24 hours to provide oxygen. Gravity had dropped from 1.135 to 1.060 in four days using EC-1118. Currently on 9 days and still some slowing signs of fermentation.

The stir plate method does really help with co2 releasing, and I think that this is probably one of the main benefits; co2 in solution has some toxic effects on yeast and mead seems to retain a lot of co2 in solution for some reason. In my experience you can add the nutrients directly into the fermenting must with minimal foaming when using a stir plate.

And if you are looking to just cut down on foaming, Fermcap-s works pretty well.

 

[Lost Tyger]

You must be an engineer, too?

I'll be honest, I'm looking for more than just cutting down on the foaming, I'm looking for reduced labor input, too. I travel a lot, and have a long commute, (insert bitching and moaning here) and when I did my first batch, I had a hard time getting back home to do the aeration, and I darn sure wasn't doing it twice a day during the work week. If I recall correctly, the suggestion was that aeration should be done more frequently, and not really worrying about how much was done at each aeration. So I thought continuous stirring would be a good way to get a little bit in at all times.

Then a friend suggested that continually bubbling air through it would be a really good way to get a little bit in at all times (works for getting oxygen into aquariums, after all).

I might put them side by side and pitch two batches and see which makes it to the 1/3 break fastest.

 

[Chevette Girl]

I might put them side by side and pitch two batches and see which makes it to the 1/3 break fastest.

If you do, please log it and post your results! Also the long-term effects like taste and aroma differences and finishing gravities...

 

[Medsen Fey]

If you do side by side batches I'll be interested to see how they turn out. Do keep in mind that yeast probably don't need aeration continuously up to the 1/3 fermentation point and that is probably putting a lot more air/oxygen into the mead than the yeast require. They only need for the must to be saturated with air about one time after the start of fermentation. Beyond that, it probably isn't adding much (and has potential for harm - though the risk is probably small as well).

 

[Tiwas]

Do keep in mind that yeast probably don't need aeration continuously up to the 1/3 fermentation point and that is probably putting a lot more air/oxygen into the mead than the yeast require.

won't it help in releasing co2?

 

[Medsen Fey]

Agitation through any mechanism will help release CO2. The question is, "does that make any difference?" I'm not convinced that it does, and there is little in the way of scientific study on the topic. CO2 under pressure does impair yeast - and it doesn't take much pressure (0.3 atm) for the effect to be seen, but I don't think constant stirring will make any measurable/significant difference in outcome. However, if data showing this comes I'm certainly open to it.

 

[akueck]

My thought about this relates to yeast starters vs. "normal" fermentation. Starters often employ stirplates to suck in as much O2 as possible. This is great, because O2 is good for making yeast. But starters are not good for making beer (mead, etc), or at least not renowned for it. Now, gentle stirring vs. pulling a vortex is certainly different. But, food for thought.

 

[Braxton]

Not only do high pitch rates cause off flavors, but excessive reproduction of the yeast, as encouraged by high oxygen levels, can also create off flavors. I'm not sure if open fermentation on a stir plate can provide oxygen levels that high, but I can easily imagine it.

"Yeast: A Practical Guide to Fermentation" says that for starters, "Continuous air from a pump and sterile filter can be quite effective... If you can set up your aeration to be sterile, not foam over, and to mix the full volume of the starter wort continuously, then it can be just as effective as a stir plate." Of course, they are just concerned with the yeast cell health and reproduction, not the flavor of the starter. They do mention that releasing co2 through agitation is beneficial, but don't cite anything or go into details. My understanding is close to Medson's, I've heard several times that co2 pressure on yeast cells has a negative impact, but haven't really read anything concrete about it. I'm guessing that the stir plate helps alleviate that stress, but I don't know enough to say if the impact would definitely be noticeable or not.

My understanding is that fermenting on a stir plate with a rubber stopper and airlock in place (which is how I'm fermenting) is essentially a closed system, with no oxygen intake occurring. But gas exchange in fermentation vessels is something I don't know much about, so that could be incorrect.

Also from "Yeast: A Practical Guide to Fermentation": "Stirred fermentors are popular in the biopharmaceutical industry for their faster fermentation, but the beer industry has shied away from them because of the fear of oxygen pickup and ester formation."

 

[Tiwas]

My (very limited and not based on science) take is that the using a low speed stir plate setup would help get the co2 out and keep the yeast suspended - which I guess would be a good thing. Any taste from the metal, yeast discomfort etc etc is something I cannot (well, I can, but I shouldn't ) comment on. Would be cool to give it a shot, though