Yeast starter - Airlock or foil?

bizarrojosh · Aug 13, 2012

So far I've been using bubble lock. I've found that out of 100 starters I make I inevitable find a fly/ant in the bubble lock in about 3% of them.

Basically I just want to know why a bubble lock isn't as good as an airlock. People say oxygen, but is there any science behind this? Sources?

Edit: Obviously yeast need oxygen to do their thing, but will 2 days in a sealed jar (bubble lock) vs a slightly sealed jar (tin foil/coffee filter) make any difference?

Marchborne · Aug 13, 2012

+1 foil for me (although I have never tried one of the foam stoppers).

One possible exception: I seem to recall hearing on a podcast (basic brewing or brewstrong), that you actually want an airlock for either brett or lacto, as oxygen is not their friend... haven't done a starter for either of those yet myself.

el_caro · Aug 13, 2012

Montanaandy said:
I have a 100% success rate using foil. Fold it to a 3x3 or so square, spray it with Starsan, fold it loosely over the top and you are good to go. Cheap & effective. Montanaandy

Same method same results here.

SpeedYellow · Aug 14, 2012

Foil = airlock. This idea that Oxygen will get into the starter when you use foil or foam smacks of homebrew myth. Considering that the yeast are giving off considerable CO2, that would tend to push any O2 right out. I suspect those in the "let oxygen in" camp have never checked or measured if it actually occurs, and if the O2 actually gets into the liquid.

If you really want more O2 into the liquid, you need to take active steps to (1) get O2 inside the jar, and (2) get that O2 into the liquid.

BWN · Aug 14, 2012

The reason you shake it or put it on a stir plate is to oxygenate it. If you use an airlock it kind of seems to defeat the purpose.

Revvy · Aug 14, 2012

SpeedYellow said:
Foil = airlock. This idea that Oxygen will get into the starter when you use foil or foam smacks of homebrew myth.

In fact I've NEVER seen anyone state this.

What WE DO SAY is the the tinfoil doesn't allow the ALREADY EXISTING OXYGEN which we put into the starter wort, to escape out the airlock, before it gets consumed by the yeast, as we want it to do. Not that more oxygen gets in. That what is in there doesn't get out.

Molybedenum · Aug 14, 2012

Oxygen is used by yeast to produce the monounsaturated fatty acids that are used to build the cell walls and store energy. You don't use an airlock, because that is a one way mechanism - it allows co2 to escape without allowing anything back in. This defeats the purpose of a stir plate (which is aimed at continuous oxygenation).

Starters are meant to propagate yeast through the aerobic process, not through fermentation.

Wynne-R · Aug 14, 2012

I use a crumpled up paper towel. I dont know if it does any better than an airlock, but its convenient, cheap and easy.

I have struggled to reconcile the notion of a CO2 blanket with what I know about partial pressure of mixed gases. George Fix, in Principles of Brewing said that CO2 coming out of solution will initially stratify, but eventually gas diffusion will restore equilibrium. So its a race with CO2 floating out the air, even as its diffusing with the air. With the volumes of gas coming off, it should pretty well blast out the air, but as the reaction slows, the air will creep back in.

For example, when you bottle, theres always going to be a little bit of air in the headspace. Eventually that air will go into solution according to the partial pressures of the nitrogen and oxygen when it ultimately equalizes.

The notion of a thin layer of CO2 keeping oxygen away is not right. In a practical sense the effect is similar. The volumes of CO2 in a fermenter will eliminate most of the oxygen. The airlock will (mostly) keep the air out.

Ultimately the question is Does the air coming into the starter have any significant effect on the oxygen level of the wort? My guess is no. Once the fermentation takes off, the air doesnt have much of a chance.

SpeedYellow · Aug 14, 2012

Revvy said:
In fact I've NEVER seen anyone state this.

What WE DO SAY is the the tinfoil doesn't allow the ALREADY EXISTING OXYGEN which we put into the starter wort, to escape out the airlock, before it gets consumed by the yeast, as we want it to do. Not that more oxygen gets in. That what is in there doesn't get out.

Several people in this thread alone said that they like foil or foam because it lets O2 in. My point is simply that using foil and making it good & tight as suggested in this thread (by you and others) is effectively the same thing as a bubbler airlock. Both work fine.

It sounds like you're saying that a bubbler airlock somehow encourages more O2 to leave the vessel as compared to tight foil. That makes no sense.

Onlooker · Aug 14, 2012

According to this article: http://www.maltosefalcons.com/tech/yeast-propagation-and-maintenance-principles-and-practices
using an airlock does indeed hinder yeast growth in a starter (cited from Ray Daniels in Figure 1). Take that for whatever you feel it's worth, but it does jibe with the commonly held theory.

If your crimping the foil down tightly then you're not going to allow much gas exchange. And keeping it kind of loose to allow gas exchange but keep out dust-borne bacteria could definitely allow a fruit fly infestation.

So how about an empty 3 piece airlock? That would seem to satisfy all the desired criteria. Of course you then have to have a stopper for the flask, if that's what you're using.

SpeedYellow · Aug 15, 2012

Onlooker said:
According to this article: http://www.maltosefalcons.com/tech/yeast-propagation-and-maintenance-principles-and-practices
using an airlock does indeed hinder yeast growth in a starter (cited from Ray Daniels in Figure 1). Take that for whatever you feel it's worth, but it does jibe with the theory commonly held theory.

If your crimping the foil down tightly then you're not going to allow much gas exchange. And keeping it kind of loose to allow gas exchange but keep out dust-borne bacteria could definitely allow a fruit fly infestation.

So how about an empty 3 piece airlock? That would seem to satisfy all the desired criteria. Of course you then have to have a stopper for the flask, if that's what you're using.

I agree there must be a better solution. Current thinking is that you get the most yeast growth with a stir plate and "loosely capped" vessel, which would then allow fruit flies. Some type of filtered air could keep out both dust-borne baddies and flies. Perhaps constant aeration from an aquarium pump with no stone would act to both oxygenate AND stir the wort, without excessive foaming.

zacster · Aug 15, 2012

I use my Mr Beer with the non-airtight lid. I don't have a stir plate so I just give it a shake every time I walk by. Shaking release a lot of CO2 from solution and as it settles back the reverse flow pulls in O2. Basically, it breathes. In theory.

SpeedYellow · Aug 15, 2012

zacster said:
I use my Mr Beer with the non-airtight lid. I don't have a stir plate so I just give it a shake every time I walk by. Shaking release a lot of CO2 from solution and as it settles back the reverse flow pulls in O2. Basically, it breathes. In theory.

Interesting uhhhhh... hypothesis. You can easily test it by installing an airlock to see if any air gets pulled in. I'm guessing you won't like the results.

But shaking alone does seem to work, or so the experts say.

zacster · Aug 15, 2012

There is no place for an airlock on a Mr Beer. I have heard it sucking in air after a good shake when it starts to settle. How much I can't say. In any case I have ended up with perfectly fine starters.

SpeedYellow · Aug 15, 2012

zacster said:
There is no place for an airlock on a Mr Beer. I have heard it sucking in air after a good shake when it starts to settle. How much I can't say. In any case I have ended up with perfectly fine starters.

No doubt your starters are fine, but it's not due to air coming in after a shake. I just now shook up an active starter, with only a tiny bit of water in the airlock, and watched the bubbles settle. No air was coming back in, just co2 exiting, the entire time.

There are really two issues here that these popular articles fail to distinguish-- shaking versus oxygenation. Both seem to be useful (?), but shaking / stirring does not equate to oxygenation! To get oxygenation, it seems we really need to actively introduce air unless we use a loose fitting cover.

papaoso · Aug 16, 2012

Shaking does oxygenate (i.e. introduce air into liquid). Not necessarily as effective as other methods, but it is a simple and adequate method. As for this tinfoil business, i'm skeptical. Seems like a sanitation no-no. Have you had success with airlocks? bc that's where i'm leaning.

SpeedYellow · Aug 16, 2012

papaoso said:
Shaking does oxygenate (i.e. introduce air into liquid). Not necessarily as effective as other methods, but it is a simple and adequate method. ...

Shaking only oxygenates to the extent that there's oxygen in the air above it. Once yeast get going, the head space is just CO2 unless it's open enough to exchange air. So if it's only CO2, then you're not oxygenating.

papaoso · Aug 16, 2012

B-b-but, tinfoil lets o2 in lol.

bizarrojosh · Aug 17, 2012

papaoso said:
Shaking does oxygenate (i.e. introduce air into liquid). Not necessarily as effective as other methods, but it is a simple and adequate method. As for this tinfoil business, i'm skeptical. Seems like a sanitation no-no. Have you had success with airlocks? bc that's where i'm leaning.

I've only used bubble locks and I've never had a failed starter.

bizarrojosh · Aug 17, 2012

EDIT: I made a separate thread for this experiment so that I don't derail this thread. Please see my experiment thread and give feed back!

Ok, Check this experiment that I'm going to conduct on my next batch of beer in 2 weeks.

Controls
I'm going to make two (2) one liter starters.
Both are going to be made from the same amount of yeast (i.e., I'll get two vials or two packets of the yeast that I am going to use and pitch in the 1 liter starter).
I will hand shake/swirl each starter evenly and exactly (i.e., if I swirl one jar five times, then I will also swirl the other jar 5 times, no more no less).
I will let the yeast starter work for 72 hours.

Variables
One starter will have a 3 piece bubble lock.
One starter will not have a bubble lock but will only be covered in tinfoil.

After 72 hours I will check the levels of yeast in the starter. These levels will then indicate which method produces more yeast.

Ok, so how does that sound? I don't have a two stir plates so they cannot be a part of this experiment. Are there any suggestions as to how to make this experiment better?

Also, is there a good way to measure levels of yeast? How should I go about doing that?

Tom-R2 · Aug 17, 2012

I have saved a lot of the little plastic cups that dip, etc. come in at restruants in our area and I simply sanitize one of them and set it inverted on top of the beaker. It acts as a shield, but doesn't seal it. I've always had good results with mine. I put some yeast from my fermenter this afternoon and am working on another 10 gallons of beer later this weekend with the same yeast.

jookos · Aug 18, 2012

I prefer foil, for purely practical reasons. I usually use iodophor for sanitation, but when it comes to starters, I feel safer putting the growlers / bottles I'm using in the oven just to be sure. In case there's some gunk I've missed that something could be hiding under, and to avoid any sort of rinsing or drying that might let dust particles to enter.

And of course, using foil you can seal the cap before placing them there. Having said that, I do use airlocks for time to time. Mostly to be able to monitor the progress of yeast of questionable quality, for instance when using something collected from commercial bottles or an outdated pack..

diS · Aug 18, 2012

I always use foil, airlock wont enable gas exchange.

chuckstout · Aug 18, 2012

I use foil, but from now on during the fruit fly season ill fix a airlock on my starter because somehow they got by the foil.

corkybstewart · Aug 18, 2012

chuckstout said:
I use foil, but from now on during the fruit fly season ill fix a airlock on my starter because somehow they got by the foil.

Same here, and lately fruit fly season lasts longer every year.

ClaudiusB · Aug 18, 2012

SpeedYellow said:
I agree there must be a better solution. Current thinking is that you get the most yeast growth with a stir plate and "loosely capped" vessel, which would then allow fruit flies. Some type of filtered air could keep out both dust-borne baddies and flies. Perhaps constant aeration from an aquarium pump with no stone would act to both oxygenate AND stir the wort, without excessive foaming.

My method, 24/7

After 1 week (WYeast 2206)

Cheers,
ClaudiusB

phoenixs4r · Aug 18, 2012

Saccharomyces said:
I've seen a coffee filter used as well. Bacteria don't have legs, they need to arrive on dust particles, so as long as you use something to keep dust out you are going to be fine.

Genius.

bizarrojosh · Aug 19, 2012

ClaudiusB said:
My method, 24/7

After 1 week (WYeast 2206)

Cheers,
ClaudiusB

What am I looking at here? Could you explain how it works? :mug:

MisterGreen · Aug 20, 2012

I have used foil and the foam stoppers and both work well. The foil is really all you need. If you're worried about fruit flies, put some apple cider vinegar in a bowl, cover with plastic wrap and poke a bunch of holes in it. No fruit fly will choose wort over vinegar. They go into the holes and get trapped.

camiller · Aug 20, 2012

Revvy said:
In fact I've NEVER seen anyone state this.

What WE DO SAY is the the tinfoil doesn't allow the ALREADY EXISTING OXYGEN which we put into the starter wort, to escape out the airlock, before it gets consumed by the yeast, as we want it to do. Not that more oxygen gets in. That what is in there doesn't get out.

Not that I like to dispute Revvy but if the foil is tight enough to prevent Oxygen in the headspace from escaping, it is also going to prevent generated CO2 from escaping, causing pressure to build up until the foil is pushed off the top.

Wynne-R said:
...I have struggled to reconcile the notion of a CO2 blanket with what I know about partial pressure of mixed gases.

I think with a continuously stirred (on a stir-plate) starter that turbulence at the air/liquid boundary is effectively continuously stirring the air as well. At least at the beginning before the thicker krusean forms. Which leads me to think that the air exchange with either a foam plug or a loose foil cap will increase oxygen getting to the starter.

Note: no science was performed in the formation of this opinion, just seems to make sense.

Yeast starter - Airlock or foil?

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