OG Reading after pitching yeast

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Afhuff01

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Are a noob mistake tonight while brewing. With the rush of a big wind storm, and waiting for my wort to cool, when I finally got the chance to pitch my yeast, I forgot to take my OG reading. I realized this about 20 minutes later, after I had already given the everything a good mixing.

How off could my OG be? I'm thinking I am worrying about nothing......
 
Depends. How much time went by after pitching before you checked? If the yeast started their job it will be off. If you let a lot of time go by, knowing how much sugar was consumed is unknown. If you checked right after pitching, it shouldn't be a problem.
 
At 20 minutes in,the yeast are still in the reproductive phase. So an OG reading at that point should be fairly accurate imo.
 
The gravity reading should not have changed more than one point. The yeast are in the lag phase. (Not the reproductive phase) During this phase the yeast are acclimating to their new environment. They take up oxygen and convert glycogen to sterols which aids in cell permeability. Reproduction occurs as long as there is available sugar.
 
Yeast reproducing only at the start of fermentation is a common misconception. Dr. George Fix explains it well in "Principles of Brewing Science." Dr. Chris White also has a nice two page paper explaining the phases.

Yeast reproduction can be expressed as a metabolic reaction. Karl Balling, in the 1800's, discovered this:

2.0665g sucrose -> 1.0g EtOH + 0.9565g CO2 + 0.11g biomass (yeast)

So as long as there is fermentable sugar, yeast is produced.
 
All true,yes. but that's not what I was referring to. Just the begining phases after pitching & before visible fermentation begins. Gotta pay attention to the stricter sense of the question asked.
 
The gravity reading should not have changed more than one point.

I think not even close. If 1point per 20min, then 24x3=72x1point= 72 points in the first 24 hours :)

The difference checking OG 20min late vs pre-pitch should be unmeasurable.

Now, contaminating your wort and scooping away a large chunk of yeast could be big issues.
 
I think not even close. ...
The difference checking OG 20min late vs pre-pitch should be unmeasurable.


Thanks, that's exactly my point. Measurement deviation from repeatability will be higher than actual change in gravity over the time period.
 
Ha ha. I think it was everyone's point. We just got bogged down in semantics.

This seems to happen a lot with certain of us,doesn't it?? Disolving the priming sugar into the fermented beer would change the gravity slightly till it ferments out in the bottles to produce carbonation.
 
What about taking a FG reading AFTER adding priming sugar? How off would that be?

You should have put a known amount of priming sugar in, so you should be able to adjust the FG based on that, or just use Woodland's approximate figure of .003. i.e. if you are using brewing software, add whatever amount of priming sugar you used to the recipe, and look at the change in OG. That would be the same as your change in FG if you are in the process of bottling and already added your priming sugar, but did not take a reading.

You could also wait until after carbing is done (if say, you realized a few days later that you forgot your FG), fill up your graduated cylinder (or whatever vessel you use when taking hydro readings) and make sure to remove all carbonation from the sample and use that as your FG.
 
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