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Old 10-07-2013, 08:19 AM   #1
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Default OG Reading after pitching yeast

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......

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Old 10-07-2013, 08:40 AM   #2
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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.

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Old 10-07-2013, 12:20 PM   #3
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At 20 minutes in,the yeast are still in the reproductive phase. So an OG reading at that point should be fairly accurate imo.

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Old 10-07-2013, 12:39 PM   #4
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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.

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Old 10-07-2013, 12:47 PM   #5
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It's been my understanding that the lag phase is the reproductive phase...

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Old 10-07-2013, 12:56 PM   #6
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... no, that's the log phase.

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Old 10-07-2013, 01:00 PM   #7
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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.

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Old 10-07-2013, 01:09 PM   #8
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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.

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Old 10-07-2013, 03:32 PM   #9
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Quote:
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.
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Old 10-07-2013, 05:33 PM   #10
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Quote:
Originally Posted by STS View Post
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.
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