Hydromiters/refractometers

[Ozbrewer]

HEy all

I asked a question a few weeksback on the cat about my hydromiter giving a different reading (after the correct equasion) to my refractomiter.....in that case it was way out, My latest brew the hydro, is saying the SG is 1009 and the refract is saying 1006, ok not a huge difference, but there is a difference...and in a brew i did last night it was a difference of 5-6 pionts on the starting gravity..... I tried another hydro and its giving a similar reading to the first, however the second hydro is calibrated at 16 deg c and the first is at 20 deg c, the Refracomiter has ATC....

ok so most will say its only a few points dont worry, and im not over concerned, but im just worndeing if the hydros are slightly out, or its the refractomiter........am i doing something wrong?, does promash have the calculations wrong?

[Dogger Dan]

Oz,

I am taking this issue to an Oracle tomorrow

Dogger

[Danno]

Hydrometers are calibrated when they're built but the ones most of us buy are a very cheap grade. Sometimes, the paper inside slips a little. Having worked around them many years ago, there are much more acurate grades of hydrometers available via lab supplies.

Have you calibrated your hydrometers? Here's a site with some good hydrometer info: http://www.honeycreek.us/SpecficGravityTables.htm. Remember to calibrate at both ends of the range because the starting point as well as the slope of the calibration could be off.

I would tend to trust your refractomer over the hydrometers. Remember to test your calibration solutions with the refractomter as well.

Once fermentation has started, the refractometer cannot compensate for the alcohol being formed. That's why there are complex calculations where the OG is needed to determine the actual gravity. The effect is similar with density for the hydrometers but would require a slightly different calculation.

[Dogger Dan]

Ok Oz

Here you go

Refractometers are calibrated to read sugar, sucrose actually. As we are using sugars other than sucrose, they refract light a bit differently so the reading will be a bit off.

Dogger

[Dogger Dan]

And the more I think on it Oz,

Is it a hand held refractometer? And if it is, do you use a monochromatic light source with a definate wavelength?

What I am saying is, if your light sources are different then the wavelength of the light being refracted is changing and different wavelengths refract differently as they move from one medium to another. Hence your results will wobble around

Dogger

[Bugeater]

And the more I think on it Oz,

Is it a hand held refractometer? And if it is, do you use a monochromatic light source with a definate wavelength?

What I am saying is, if your light sources are different then the wavelength of the light being refracted is changing and different wavelengths refract differently as they move from one medium to another. Hence your results will wobble around

Dogger

I noticed this on my last brew. I checked it outside in bright sunlight at the end of the boil and again indoors after the wort was cooled. Noticed a little difference, but I figured it was just a beer induced variation in perception.

Wayne
Bugeater Brewing Company