Help with low SG and fast fermentation

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David Woods

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Hi, looking for a bit of info on my all grain brews.

This is the 3rd all grain kit I have brewed and I seem so be getting a low SG before ferment - I am following the instructions carefully but this last brew showed 1050 at the end of the boil (I let the sample cool) but later showed 1043 instead of the expected 1046 so I guess something went a bit wrong. The recipe was for 25L but I made it at 23L so I would have expected a higher SG. All correct temps were hit finishing with a 20 min whirlpool for flameout hops. Any help with getting the mash to the correct SG would be helpful. Any tips on what to check at the end of the mash/boil in case it needs to go longer.

This same brew has fermented vigorously for 2 days and seems to have finished as 1015 - higher than the expected 1008. This is the second brew that fermented really fast - the temp is controlled perfectly. I realise things are probably still going and I will need to leave it to clean up etc but the last batch stayed at the higher SG despite pitching more yeast and leaving for two weeks.

Both brews used Lallemand yeasts and did the same fast ferment - US-05 doesn't go so quickly. Anyone had issues with Lallemand?

Any help would be great as this also seems to give a low carbed beer - yeast not good enough maybe? I batch carb using a batch calculator - e.g. 23L @21 deg for a 2.5 vol = 160g Dextrose.

Thanks
 
Last edited:
Two points out is nothing. Your equipment isn't the same as the guy's who wrote the instructions so you can expect a bit of variation.
It won't have finished after a couple of days. Leave it other 10 days then check it.
 
Are you by chance measuring specific gravity using a refractometer, and not a hydrometer?

If yes, we can help you with that later. Misuse of a refractometer is an extremely common problem.

If not, you might need to check calibration of your mash thermometer in both ice water and boiling water to see how far off it is from 0C and 100C. If your mash thermometer is far off, you might be mashing a lot hotter than you thought. Doing so would kill your enzymes and thus limit fermentability of the sugars in your wort.
 
I measured with a hydrometer - reading the comments I am thinking the mash temp may have been a bit high, 68 instead of 66 at the start - would that be enough to mess with enzymes?

My thermometer is new - a Catertemp which I see a lot of brewers using but I will check it.

as I am using an AIO I can only go as high as the unit will go in terms of boiling but it does seem a good rolling boil.
 
The higher the temperature the lower the viscosity, so the temperature differential would account for two different readings for the OG.
If your mash temperature was 66C and didn't go higher than 68C then it could be your grain crush, but your high FG points to mash temperature being higher than you thought?
I don't look for a fast take-off and finish of the yeast, my preference pitch low and let the yeast settle in for 12 to 24 hours, last thing I want is an ester bomb.
 
The higher the temperature the lower the viscosity, so the temperature differential would account for two different readings for the OG.
If your mash temperature was 66C and didn't go higher than 68C then it could be your grain crush, but your high FG points to mash temperature being higher than you thought?
I don't look for a fast take-off and finish of the yeast, my preference pitch low and let the yeast settle in for 12 to 24 hours, last thing I want is an ester bomb.
I assume by "pitch low" you mean pitch the yeast with the wort at the low end of the temperature range for the yeast?
 
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