Every brew, I pull a sample out of the BK once I've collected all my pre-boil volume to do a pre-boil gravity check. Because I have the heating element running the entire time I'm lautering to the kettle, by the time I've collected pre-boil volume, it's usually right around 205-206F. So, I pull the sample out and let it sit in my hydrometer tube while I baby sit the boil for the first period of time, to add hops and make sure I don't have any boil overs. Once it's under control and I don't have to worry about it, I go and check pre-boil gravity.
Now obviously, the hydrometer will read differently at ~130-140F than it will at room temp, so I know to use the calculator to figure out the real reading.
Two times now, I've checked pre boil gravity, used the calculator to figure out the real reading at that temperature, and then used the dilution and boil off calculator to figure out what my expected OG will be after the boil is complete and the number has been way off. For example, on my brew this past sunday, I was targeting a final OG post boil of 1.042...
- Pre-boil sample was at 132*F at time of checking
- Hydro reading was 1.038
- Corrected value based on Brewers Friend calculator was 1.049
- Knowing that I boil off ~1 gallon during the boil, Brewers Friend boil off calculator told me I'd be at 1.052 OG.
I confirmed I did boil off ~1 gallon (based on etched gallon markers) and OG came out at 1.045.
So, here's my question: I know hydrometers aren't accurate at those temps, but can they REALLY be that far off on a hot sample?
I am running a Spike Brewing steam condenser lid and my first thought was that water from the steam condenser was running back into the kettle. However, if this was true, 2 things would be happening...
- I'd be able to see the water flowing back in when I pull the 4" clear cover off and look in there with a flashlight during the boil. I always check just because I'm paranoid and there's never any water coming back into the kettle.
- My post boil volume would be higher than my pre-boil volume, assuming the hydometer reading was accurate. The only way the OG could be lower than my corrected pre-boil boil reading would be more volume, and that is definitely not the case.
So in my head, that leaves one option - the hydrometer at that temperature is just really unreliable.
Would you agree?
Now obviously, the hydrometer will read differently at ~130-140F than it will at room temp, so I know to use the calculator to figure out the real reading.
Two times now, I've checked pre boil gravity, used the calculator to figure out the real reading at that temperature, and then used the dilution and boil off calculator to figure out what my expected OG will be after the boil is complete and the number has been way off. For example, on my brew this past sunday, I was targeting a final OG post boil of 1.042...
- Pre-boil sample was at 132*F at time of checking
- Hydro reading was 1.038
- Corrected value based on Brewers Friend calculator was 1.049
- Knowing that I boil off ~1 gallon during the boil, Brewers Friend boil off calculator told me I'd be at 1.052 OG.
I confirmed I did boil off ~1 gallon (based on etched gallon markers) and OG came out at 1.045.
So, here's my question: I know hydrometers aren't accurate at those temps, but can they REALLY be that far off on a hot sample?
I am running a Spike Brewing steam condenser lid and my first thought was that water from the steam condenser was running back into the kettle. However, if this was true, 2 things would be happening...
- I'd be able to see the water flowing back in when I pull the 4" clear cover off and look in there with a flashlight during the boil. I always check just because I'm paranoid and there's never any water coming back into the kettle.
- My post boil volume would be higher than my pre-boil volume, assuming the hydometer reading was accurate. The only way the OG could be lower than my corrected pre-boil boil reading would be more volume, and that is definitely not the case.
So in my head, that leaves one option - the hydrometer at that temperature is just really unreliable.
Would you agree?