hungupdown
Well-Known Member
Usually, my digital refractometer readings make sense.
But at the moment, successive/repeat measurements taken, on the same sample(s), always keep going up. Maybe from brix 17% to 22% over around 3 minutes. This is with samples from a fermenting, high gravity/ABV imperial stout. Present: OG 1143; corrected SG 1026; ABV 14.5%
Normally after putting a sample on the refractometer, I leave it a minute or two before taking a reading. This allows the sample to reach the same room temperature as the refractometer (normally 17-19°C here, this value is used for temperature correction).
Correction needed is larger when sample temperature is much higher than room temperature (eg during mash, it would be around +3.1). Successive/repeat readings should rise slightly, as a sample drops to room temperature.
But at my fermentation temperature (currently 23°C), the correction to Brix @20°C is quite small, eg brix 20 @23°C is brix 20.2 @20°C. So an immediate reading, while still 3°C too hot, would only be marginally low (correction needed +0.2).
Another factor, can be evaporation while cooling, (greater with a hot sample), increasing the density.
But I have readings going up, by way more than any temperature correction! And it's too cool for much evaporation. I've closed my refractometer sample cover to prevent evaporation anyway (to no avail).
Using the reading taken, immediately after putting the sample in, seems to give the most accurate result. With corrected SG then being a close match to a hydrometer reading.
I've already tried cleaning the prism surface, as there looked to be some dry deposit (sugars?) around the edge.
Stirring the sample, seems to be the only thing that brings readings back down (but never quite as low, as the initial one).
After emptying sample, and checking cal with water, readings then stay consistant.
Could the effect be from fermentation gas bubbles, adhering to the prism.
But at the moment, successive/repeat measurements taken, on the same sample(s), always keep going up. Maybe from brix 17% to 22% over around 3 minutes. This is with samples from a fermenting, high gravity/ABV imperial stout. Present: OG 1143; corrected SG 1026; ABV 14.5%
Normally after putting a sample on the refractometer, I leave it a minute or two before taking a reading. This allows the sample to reach the same room temperature as the refractometer (normally 17-19°C here, this value is used for temperature correction).
Correction needed is larger when sample temperature is much higher than room temperature (eg during mash, it would be around +3.1). Successive/repeat readings should rise slightly, as a sample drops to room temperature.
But at my fermentation temperature (currently 23°C), the correction to Brix @20°C is quite small, eg brix 20 @23°C is brix 20.2 @20°C. So an immediate reading, while still 3°C too hot, would only be marginally low (correction needed +0.2).
Another factor, can be evaporation while cooling, (greater with a hot sample), increasing the density.
But I have readings going up, by way more than any temperature correction! And it's too cool for much evaporation. I've closed my refractometer sample cover to prevent evaporation anyway (to no avail).
Using the reading taken, immediately after putting the sample in, seems to give the most accurate result. With corrected SG then being a close match to a hydrometer reading.
I've already tried cleaning the prism surface, as there looked to be some dry deposit (sugars?) around the edge.
Stirring the sample, seems to be the only thing that brings readings back down (but never quite as low, as the initial one).
After emptying sample, and checking cal with water, readings then stay consistant.
Could the effect be from fermentation gas bubbles, adhering to the prism.
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