How use gravity readings to detect ferment activity?

[gkeusch]

I cold crashed a starter, took it out of the fridge for four hours, then pitched it. I had no visual activity (and I mean none - cap still sitting firmly on post) in my airlock after 24 hours and panicked. In a previous thread I was told it was most likely OK, just taking time to wake up. Somebody asked if I had taken a gravity reading - I hadn't, but it didn't occur to me that any significant change in gravity (as in measurable with my standard hydrometer) could be detected without corresponding co2 activity. Is that not right?

 

[kapbrew13]

How long did your starter go?
Did you bring the cold crash back to room temp before dumping in brew?
If you start a starter with 1.040 gravity liquid, after the starter finishes, the gravity should be lower then 1.040. That's because yeast ate the sugars while growing.

 

[duboman]

No need to panic! 24 hours is not a long time and there are various factors involved such as pitch temp,, aeration of wort, fermentation temperature, size of starter, etc. Typically if you pitch cold the yeast takes a bit to acclimate and go through the growth phase as they gear up to begin actively fermenting your beer.

If things go 72 hours and still appears nothing is happening then take a reading. You could also have a leaky seal in the bucket lid allowing the gas to escape from somewhere other than the airlock.

 

[AmandaK]

...but it didn't occur to me that any significant change in gravity (as in measurable with my standard hydrometer) could be detected without corresponding co2 activity. Is that not right?

That is incorrect. You're assuming that you can see the CO2 gas. Can you see it escaping an airlock? Yes. But what if you have a leak? You won't see it then.

Take a hydrometer reading. If things go three days without change in gravity, consider pitching another lot of yeast.