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colonel2jays

SG increase on ferment

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Hey all, has anyone ever experienced an increase in SG on their ferments?

Yesterday (day 5) I had 1.009 and today I have 1.011! I've never seen this before. The product is a wheated bourbon-style mash with the grains separated from the wort prior to fermentation. The total volume in the tank is ~6000 litres, with 1480L of that having begun wild yeast fermentation two days before 4.5kg dry yeast was pitched.

Is it possible that fermentation has stopped and somehow we're still getting secondary starch conversion?

Thanks in advance!

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Did you temperature correct your sample? Earlier in the fermentation it will be hotter, and therefore read lower then if the same sample is cooled to closer to the calibration temperature on your hydrometer.

Also a potential cause, were your first or second samples actually a representative sample?

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I have had stratification, ie it’s not fully mixed and if you check by pulling off the top you get a false reading.  The yeast mixes it up better and the reading goes up since the wort is now mixed and the denser wort is now evenly distributed. 

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On 6/13/2019 at 10:17 PM, Tom Lenerz said:

Did you temperature correct your sample? Earlier in the fermentation it will be hotter, and therefore read lower then if the same sample is cooled to closer to the calibration temperature on your hydrometer.

Also a potential cause, were your first or second samples actually a representative sample?

Tom, thanks for your reply.

The temperature difference between the two readings was only 0.9C so that's not it. 

The samples were taken from a sample port about 18" from the base of the tank. I'd like to think that can be called a 'representative' sample. I even took a second sample of the 1.011 product as a sanity check.

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On 6/14/2019 at 12:08 AM, bluefish_dist said:

I have had stratification, ie it’s not fully mixed and if you check by pulling off the top you get a false reading.  The yeast mixes it up better and the reading goes up since the wort is now mixed and the denser wort is now evenly distributed. 

Bluefish, thanks for your reply.

I certainly can't rule out stratification, but after 5 days in the tank I'd have thought all of the distribution of wort that was going to happen would have happened already!

It's also important to note the gravity didn't change from 1.011 in the days after, so it's safe to assume the batch was no longer actively fermenting on day 6.

Does anyone have any thoughts on my 'secondary conversion' hypothesis?

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Depending on your cook process, it is likely starches will continue to break down. As a result finished gravities can and often are below 1.000.

The only way I could see a mash getting more dense (increased gravity) is if you lose alcohol. It seems more likely that your sampling procedures explain the variance. 

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I feel like it's a measurement error or continuation of the enzymatic conversion. Some enzymes are still active as low as 70f.

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