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Jun 08, 2022 View:

SG increase on ferment

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!


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?


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. 

Reply:On 6/13/2019 at 10:17 PM, Tom Lenerz said:
Reply:On 6/14/2019 at 12:08 AM, bluefish_dist said:

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. 


I vote for Tom's explanation.  Occam's razor.  Simplest answer is the often the right one.  Measurement error.


Thanks guys. Now to take steps to improving my fermentation performance...


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


sorry to resurrect Lazarus here but I wanted to chime in. also, a caveat: I imagine for most users on the form will not find this applicable but it does happen. 

-  I noticed in the OP that wild yeast was a variable.  This may or may not be relevant to your situation but I have had ferments where their SG increased, at least nominally.  All of our ferments were wild and some would have further "infections" - particularly from a poorly cleaned sugar cane mill - would cause exceptionally thick, viscous ferments. 


Pediococcus - nice call


With pedio over time you should be able to see with platelets on the top of the ferment, right?  Was this a grain on or off fermentation?  Depending on how the sample was prepared with grain present, that could change the reading.  Usually with hydrometers it's an error as many others have pointed out.