So, the concensus about starters is to only use tinfoil so that oxygen can get in. If that's the case, then why is it so important to use an airlock when brewing? Why couldn't you just use tinfoil again? Or a loose screw-on cap? It seems like if it can't contaminate a starter, then it can't contaminate the wort. Is there another issue involved? Something about not getting oxygen in the beer?
Why use airlocks for brewing and not for starters?
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Yeast reproduce in the presence of O2. In a starter O2 is good, because you want them to reproduce as much as possible. Since you won't be drinking the starter, the O2 isn't a big deal.
In beer, O2 during fermentation will ruin your beer. The airlock keeps it out. Foil will work, but not as well as an air lock.
In beer, O2 during fermentation will ruin your beer. The airlock keeps it out. Foil will work, but not as well as an air lock.
DurtyChemist
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Yup. You WANT oxygen to build more yeast cells. You aren't worried about the taste of the beer made from a starter. If you only wanted to grow more cells you'd focus on that. Since we want flavors and attenuation in beer we focus on that during fermentation.
flars
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You can ferment in a carboy with a foil cap or the type of buckets which utilize no air lock at all. The wort is aerated so the yeast has oxygen to use during the reproductive phase. Once the reproductive phase ends the fermentation is anaerobic. CO2 production will form pressure in the fermentor and escape around a foil cap. The airlock provides extra protection from bugs and flies which can crawl underneath the foil to get at the good smelling fermenting beer.
GrogNerd
mean old man
in a starter, we want the yeast to breathe
in our beer, we want them to eventually suffocate
in our beer, we want them to eventually suffocate
Aristotelian
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I thought foil more or less keeps oxygen out like an airlock. It is a rudimentary airlock. When your starter ferments, it is emitting C02. As long as the flask/jar is not disturbed, it is going to have a C02 barrier. The benefit of an airlock in a carboy is you can use the bubbles to gauge fermentation and have a good (not perfect) idea of when it is done fermenting, which you are not worried about with a starter.
Um... no.
The foil just keeps any critters from possibly falling in. The foam stoppers are much better than foil, but foil is cheaper. Lol!
CO2 blankets are a myth.
An airlock let's gasses escape, and hopefully nothing to come in.
Never trust an airlock to tell you fermentation is complete.
The point of foil is to allow some air through. It's meant to keep out airborne contaminants (dust and such) carrying wild yeast and bacteria as well as insects like fruit flies that also could carry wild yeast and bacteria. I prefer to use foam stoppers instead of foil, for the same reason. As these folks said, the point of a starter is to grow a maximal amount of healthy yeast, not to produce a good tasting product. Where the point of the whole batch is obviously a good tasting product. As such, they have different requirements WRT oxygen.
In a starter you want as much gas exchange as possible without contamination. If you can use a clean room (some pros have them, most of us homebrewers do not) where airborne contaminants are not an issue, you'd get the best growth by doing your starters completely uncovered. And you definitely don't want your starter sitting undisturbed. If you're not doing your starters on a stir plate, you should at least be swirling them every time you walk by to keep introducing more oxygen.
But, once your yeast have performed their growth operations in the main batch, the only thing that oxygen is going to do is stale your beer. This is why you aerate before you pitch, and then do anything you can to reduce oxygen access from there on until the beer's in your glass.
The issue is that CO2 doesn't just sit there. Gasses will mix over time, and the blanket of CO2 would eventually mix with other atmospheric gasses. But it happens too slowly in a starter (you need oxygen more rapidly than that), and an airlock in the beer will prohibit it happening at all. If you do choose to ferment open, with using foil instead of an airlock most closely resembling open fermentation (a number of both pros and homebrewers do it, I haven't tried it personally but something I've been meaning to experiment with), it's common practice to then seal the fermentation with an airlock after the active phases when CO2 is no longer being produced at a rapid rate. You definitely don't want to just leave the foil on there the whole time.
In a starter you want as much gas exchange as possible without contamination. If you can use a clean room (some pros have them, most of us homebrewers do not) where airborne contaminants are not an issue, you'd get the best growth by doing your starters completely uncovered. And you definitely don't want your starter sitting undisturbed. If you're not doing your starters on a stir plate, you should at least be swirling them every time you walk by to keep introducing more oxygen.
But, once your yeast have performed their growth operations in the main batch, the only thing that oxygen is going to do is stale your beer. This is why you aerate before you pitch, and then do anything you can to reduce oxygen access from there on until the beer's in your glass.
The issue is that CO2 doesn't just sit there. Gasses will mix over time, and the blanket of CO2 would eventually mix with other atmospheric gasses. But it happens too slowly in a starter (you need oxygen more rapidly than that), and an airlock in the beer will prohibit it happening at all. If you do choose to ferment open, with using foil instead of an airlock most closely resembling open fermentation (a number of both pros and homebrewers do it, I haven't tried it personally but something I've been meaning to experiment with), it's common practice to then seal the fermentation with an airlock after the active phases when CO2 is no longer being produced at a rapid rate. You definitely don't want to just leave the foil on there the whole time.
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+1 on a foam stopper well soaked in star-san and squeezed.
Much preferable to foil.
Much preferable to foil.
Um... no.
The foil just keeps any critters from possibly falling in. The foam stoppers are much better than foil, but foil is cheaper. Lol!
CO2 blankets are a myth.
An airlock let's gasses escape, and hopefully nothing to come in.
Never trust an airlock to tell you fermentation is complete.
CO2 blankets are not a myth. With a density of about 1.5 times as much as air, CO2 does blanket your beer it undisturbed. If you don't believe it, do a ferment in a chest freezer and let it have three weeks in there, then open the lid carefully, stick your head in, and take a sniff. Try not to pass out from inhaling the CO2 that remains in the freezer.
Woodland Brews says otherwise. If you stir in some oxygen when you add the yeast, you'll end up with the same amount of yeast as if you stirred it with a stir plate but it will take longer. http://www.woodlandbrew.com/2015/02/yeast-starters-stirred-vs-not.html
WrQth
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Wouldn't that be more of a displacement of air in the chest freezer with C02 produced by the yeast? convection currents would do the mixing.
WrQth
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But it doesn't speak to the vitality of the yeast which is another factor which can contribute to a good fermentation.
SeraW
she/her
It's called an open fermentation. May be a good idea in some cases, but definitely get an airlock on before the end of fermentation.
Yes, they are. Watch the video. Br2 has a molecular weight of 159.8 vs. air at (0.21 * 32 + 0.79 * 28) = 28.8, for a ratio of 5.54. The Br2 in the video mixes completely with air in about 30 minutes.
[ame]https://www.youtube.com/watch?v=_oLPBnhOCjM[/ame]
The chest freezer is (almost) sealed, so that as CO2 is formed, it pushes air (and CO2) out of the freezer, but little air can diffuse back in, thus CO2 builds up in the closed space. Open the lid for about a half hour, and try your experiment again.
Brew on
Only place I've ever seen that is him. His supporting data even quotes himself. I don't buy it.
All other data I've seen says otherwise.
Yep. A chest freezer has a nice seal... so your example is valid. But not the norm.
Edit: Looks like this has already been addressed above...
The key point here is gas exchange. If the chest freezer seals up and doesn't allow much, then yeah, all the CO2 stays inside.
Same thing as....an airlock! Aha!
I'm actually thinking of making a change to my setup. Something I occasionally think of but then always forget to actually do. Pulled from Kai's data on access to oxygen and actual measured cell counts, especially when doing a very large starter for a beer where I really want a big pitching rate, I pump filtered air into my starter headspace via an aquarium air pump while they're on the stir plate (I aerate my wort for full batches with pure O2 though, but had the pump from years ago before switching). Air tube goes down alongside the foam stopper in the flask. However I noticed that it leaves just enough opening between the air tube, stopper, and flask neck that a zealous fruit fly could climb all the way through. So I may pick up some drilled stoppers sized for my flasks, drill holes sized for my aquarium pump tubing, and then actually pump air in with an airlock. Constant fresh air, no bugs, and the airlock would then keep any mentionable pressure from building up. While I'm at it I should probably rig up that blowoff faux-Burton Union system.
Yes, they are. Watch the video. Br2 has a molecular weight of 159.8 vs. air at (0.21 * 32 + 0.79 * 28) = 28.8, for a ratio of 5.54. The Br2 in the video mixes completely with air in about 30 minutes.
https://www.youtube.com/watch?v=_oLPBnhOCjM
The chest freezer is (almost) sealed, so that as CO2 is formed, it pushes air (and CO2) out of the freezer, but little air can diffuse back in, thus CO2 builds up in the closed space. Open the lid for about a half hour, and try your experiment again.
Brew on
In my physics class we were taught that it took more time for that diffusion to occur because the mixing depended on brownian motion to mix the gasses. Perhaps there is more to it or perhaps the books were wrong (shock!!). In the video the bromine mixes completely with the air in the tubes but it was explained that that took half an hour. I usually don't leave my fermenter open for long when taking a sample so I still feel there is a blanket protecting my beer.
kombat
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Why?
dyqik
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Diffusion is only dominant in completely still gases. There are nearly always drafts of air that cause much more mixing than diffusion alone can provide, particularly if there is any kind of temperature gradient around, or you've moved a lid or door. Like when you open a fermentation chamber, and then the lid of the fermenter, to expose the beer that's at a different temperature to the room.
I see this in my lab all the time - we use liquid nitrogen in open coolers as cold loads, and there's a smooth boundary layer between the cold nitrogen boil-off (at not much above 77K) and the room temperature air, visible by the water vapor forming at the boundary. Almost anything can disturb that layer, e.g. just walking past, or flipping a page in a notebook. In our case, this leads to a build-up of oxygen dissolved in the liquid nitrogen, which raises the boiling point by several degrees.
GrogNerd
mean old man
ok, take the physics derail over to the "funny things overheard about beer" thread
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Me too!
I just hate it when that happens in my lab....
Oh.. wait.. was this about what kind of top to put on your Erlenmeyer flask?
Aristotelian
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In my opinion, when the beer is actively fermenting and emitting C02, the headspace is going to be mostly C02 even if the seal is not airtight. Surely all would agree that the headspace at that time is mostly C02 and the foil will help keep it there.
Once it stops is irrelevant. The C02 may leak out or not. At that point the beer is fermented and less prone to contamination. If you were fermenting a beer for a month you might not want to risk it with foil, but for a starter that you are going to use in a few days it's going to be fine.
Once it stops is irrelevant. The C02 may leak out or not. At that point the beer is fermented and less prone to contamination. If you were fermenting a beer for a month you might not want to risk it with foil, but for a starter that you are going to use in a few days it's going to be fine.
While what you're saying isn't incorrect, you're missing the point.
A CO2 barrier is both not necessary and not desirable in a starter (despite whatever woodland brews' outlying opinion says). You want oxygen there.
A CO2 barrier is both not necessary and not desirable in a starter (despite whatever woodland brews' outlying opinion says). You want oxygen there.
Aristotelian
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I give mine a good shake to get it started, just like with a regular beer. Once it starts I doubt there would be any difference. Certainly beer in a primary fermenter with an airlock does not need more oxygen coming in. Have you done a side by side to show that yeast do worse using airlocks? I always thought the foil was just for convenience.
By the way, the explanation I have heard for stir plates (which I have never used) is to keep yeast in suspension, not to oxygenate.
Anyway, this has been beaten to death on other threads already. The bottom line, we all agree tin foil is the way to go for whatever reason.
https://www.homebrewtalk.com/showthread.php?t=155763
I haven't. Others have. On my phone and not going to link it, but Kai Troester (BrauKaiser) did a study with cell counts, comparing identical starters between airlock, foil, injected air, and uncovered. The growth lined up in that order, with the airlock having the least and uncovered having the most. However an uncovered starter obviously has an unacceptable contamination risk so isn't practical, leaving injected air as the best practical option for optimum growth.
Your fermentation chamber no doubt has a very high concentration of CO2, but it also has enough O2 to oxidize your beer over a matter of days. Normal atmospheric O2 concentration is about 210,000 ppm, but beer will oxidize with less than 1 ppm in the headspace. You can get rid of 90% of the O2, and still have more than enough to oxidize your beer. And whatever O2 is in your fermentation chamber is pretty uniformly distributed throughout. There will be no stratification.
Brew on
Your fermentation chamber no doubt has a very high concentration of CO2, but it also has enough O2 to oxidize your beer over a matter of days. Normal atmospheric O2 concentration is about 210,000 ppm, but beer will oxidize with less than 1 ppm in the headspace. You can get rid of 90% of the O2, and still have more than enough to oxidize your beer. And whatever O2 is in your fermentation chamber is pretty uniformly distributed throughout. There will be no stratification.
Brew on
Sorry but this isn't adding up for me. I brew a batch of beer, let it sit in the fermenter for 2 weeks. Hopefully the yeast used up all the oxygen in that headspace and now all that is in there is CO2. I open the lid, take a hydrometer sample, decide the beer is done and now I add my dry hops. During the time my fermenter was open I had to have introduced oxygen, no way to avoid it, and when I add the hops I get more oxygen carried in with the pellets. I let it sit for another week, take the lid off and transfer the beer to the bottling bucket (again, open top) and begin bottling. As I fill bottles, more air has to be sucked into the bottling bucket. Now I must have more than 1ppm of oxygen in the bottling bucket and some of that has to have dissolved into the beer. Why are my beers drinkable at all? I've never had a cardboard tasting beer.
100% certain there is going to be oxidation. However, slight enough that it's below taste threshold now and may only become apparent significantly down the line, if at all.
Hell I'd venture it's possible that like diacetyl, DMS, tannins and acetaldehyde, micro levels of oxidation present well below threshold help form the total "beer" character and beer may taste off without them. Just a theory.
I don't know how much oxidation it takes to get to the cardboard taste stage. Apparently there is a broad range of oxidation levels that ranges from barely perceptible to yuck. It's reported that 3 weeks of storage at room temp with 0.15 ppm O2 in the beer will lead to perceptible flavor changes in IPA's (page 21 of http://www.craftbrewersconference.com/wp-content/uploads/2015_presentations/F1540_Darron_Welch.pdf.) I doubt my palate is sensitive enough to detect what they are talking about.
It's very likely that almost all homebrew (and probably a lot of commercial) beer is oxidized to some extent. If you are happy with the taste and storage life of your beer, then it is not too oxidized for you, and there is no need to try to reduce the O2 exposure of your beer. There are however, several threads on HBT from hoppy beer brewers who complain about the bland taste of their brews, and much of that may be due to oxidation issues. Some brewers report improvements in their hoppy beers after doing more to control O2 exposure.
The question of how much oxidation is too much is very different from how much O2 is actually present in a brewing process. Actual O2 is measurable, and in some cases calculable (i.e. quantitative.) Taste is subjective (qualitative) and not subject to definitive measurement.
Brew on
