Weird Goings On In The Airlock

[TBird]

Hi All

I've been fermenting a starter in my fridge at around 20 degrees (stepping it up for about a week). On a couple of ocassions now I've opened the fridge and saw very slow activity in the air lock. As I've reached out to remove the starter (thinking it's time to pitch) the activity in the airlock increases (I'm talking no more than 5 secs after I've opened the door).

Now, I've always thought that there was a slight vacum in a fridge when the door was closed and therefore there shouldn't be a build up of pressure from the starter creating CO2. But this is what it looks like with the co2 rushing through the airlock when the pressure from opening the door is released.

So what gives??

Thanks

 

[felten]

You really shouldn't be using an airlock in a starter anyway h34r:

 

[gap]

You really shouldn't be using an airlock in a starter anyway h34r:

Why not???

 

[adryargument]

Probably the fridge and starter are both slightly pressured.
As soon as you open the door they unpressurise = CO2 coming out the airlock?

It doesnt take much to make the airlock 'bubble'

 

[unrealeous]

I've been fermenting a starter in my fridge at around 20 degrees (stepping it up for about a week). On a couple of ocassions now I've opened the fridge and saw very slow activity in the air lock. As I've reached out to remove the starter (thinking it's time to pitch) the activity in the airlock increases (I'm talking no more than 5 secs after I've opened the door).

Now, I've always thought that there was a slight vacum in a fridge when the door was closed and therefore there shouldn't be a build up of pressure from the starter creating CO2. But this is what it looks like with the co2 rushing through the airlock when the pressure from opening the door is released.

So what gives??

Vacuum in the fridge - were it the case - would cause air to rush INTO your starter when you opened the door.

What is more likely is the mechanical action of you opening the door is enough to rock the starter - like giving it a little shake - causing C02 to come out of solution.

 

[Wolfy]

Why not???

You can use an airlock if you wish, however most people find them more of a Nuisance than anything useful or required.
Depending on the container you are making your starter in, most people find it quicker, easier and better to use something simple like gladwrap or aluminum foil.

 

[QldKev]

noooooooooooo, not kittens in the airlock!


QldKev

 

[Ducatiboy stu]

I havent used an ailrlock for years....got sick of loosing kittens... h34r:

 

[stux]

Open the pod bay doors HAL

 

[Lecterfan]

Open the pod bay doors HAL

Best reply ever.

Champagne comedy.

edit: come on! Am I the only one to think that reply was both insanely clever AND amusing? Am I the only about to crack open another bottle of ESB and watch 2001 again? Or maybe just the first 5 mins of Mel Brooks' History of the world to watch men in ape suits jack off? Probably...

 

[felten]

The increased pressure isn't good for yeast growth (too much pressure will kill them, though a airlock won't get that bad), al foil over the top is perfectly fine.

 

[TBird]

The increased pressure isn't good for yeast growth (too much pressure will kill them, though a airlock won't get that bad), al foil over the top is perfectly fine.

I know that using a airlock isn't foolproof,but I like to use it as an indication of how the yeast is travelling ie is the starter reaching its end and ready for pitching.

Cheers

 

[Wolfy]

I know that using a airlock isn't foolproof,but I like to use it as an indication of how the yeast is travelling ie is the starter reaching its end and ready for pitching.

Airlock activity has little bearing or relevance when making a starter to grow yeast. If you were using a sample of unknown viability it may provide some sign of fermentation activity but there are usually enough other visual signs to determine that.

After acclimatization, yeast enter a growth phase where they consume nutrients and oxygen, there is not (as far as I am aware) any visible air-lock-related indication that the yeast are reproducing happily. However for maximum growth you should provide the yeast with excess oxygen (which is why many people use a stir-plate), but if you were to use an airlock you'd have no exchange of oxygen with the atmosphere and so a loose fitting cover (like aluminum foil) which does allow air-exchange would be better.

After about 12-48 hours (usually closer to 12) the yeast start to ferment the wort, and this is when the airlock will start to bubble. In theory, when you see the first bubbles in the airlock it's after the yeast have already reproduced as much as they are going to. If you are gong to pitch the new yeast immediately, you do not need to wait for fermentation to finish (a slow/stop airlock activity), so there is no reason or advantage to ferment out the starter or to watch or wait or monitor the airlock activity.

If, however, you were not planning to use the starter immediately, or if you were not on pitching the yeast into a similar wort, allowing the yeast to first ferment, settle and build up their reserves (about 2-3 days after the fermentation/airlock bubbling stops) then there might be some advantage for monitoring airlock activity, but most often starters are grown and used almost immediately.

 

[TBird]

Thanks Wolfy

Well explained and now I can see how it all fits together and makes sense. Just one other question. At what stage in the fermentation process should you step up the starter ie add more wort to it to increase the cell count?


Cheers