Hydrometer vs Refractometer for OG

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timtoos
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Hydrometer vs Refractometer for OG

Post by timtoos » Sat Oct 14, 2017 7:24 am

Hi,

I have both a hydrometer and digital milwaukee refractometer (MA871) and find these units both tie up pretty good for OG.

Yesterday, I did a brew and my hydrometer, which I hate using and always reads +1 point high across the range) read a OG of 1050 so 1049 and my refractometer read 13B or 1053.

Which instrument would you guys trust more?

PS, the sample was at 21C on the hydrometer and given well chance to hit room temperature on the refractometer.

TIA

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Re: Hydrometer vs Refractometer for OG

Post by PeeBee » Sat Oct 14, 2017 9:51 am

A hydrometer measures gravity (density). It doesn't care what's creating that gravity relative to pure water, whether it be sugar, alcohol, battery acid, ... . The SG scale is "native" to the likes of hydrometers.

A refractometer measure the degree of light bending in a liquid. Fruit growers and the like latched on to the fact that light bends in a predictable way in glucose sugar solutions. They often use the Brix scale to record this bending. It does care what's creating the bending and light bends differently in a solution of glucose, maltose, alcohol, mixtures of these, ... . The SG scale is NOT native to refractometers, hence you have scales to adjust the indicated reading.

So, if worried about gravity readings a hydrometer always tells you what you want. But compared to refractometers they are a pain to use and much easier to break. Whichever tool you use there are going to be compromises, but either is more than adequate for our purposes (just make sure you use a conversion table when using refractometers on fermented liquid).

To avoid dilemmas, use just one tool and put the other in a cupboard out of sight.
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Hydrometer vs Refractometer for OG

Post by f00b4r » Mon Oct 16, 2017 8:35 am

That makes the assumption that his hydrometer is accurate and precise. Making up a known strength solution(s) with sugar and then measuring might help him decide which he wants to believe or if replacement/calibration is needed.

EDIT: I week probably get corrected on my use of accuracy and precision (it's a little early here after a long night) but I am sure you can get the idea.

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Re: Hydrometer vs Refractometer for OG

Post by Aleman » Mon Oct 16, 2017 9:47 am

With a decent correction formula the refractometer. ;) Look Up Sean Terrils work ;)

I still use both, but I do have a nice 0.990 - 1.020 hydrometer for finishing gravity readings

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Re: Hydrometer vs Refractometer for OG

Post by orlando » Mon Oct 16, 2017 9:49 am

PB is quite right and could go further by saying that if are to get your refractometer to match your hydrometer you have to recalibrate for each wort for all the reasons he gave. Each wort is going to be slightly different depending upon what you are brewing. Graham Wheeler has an interesting take on it in the notes to his Beer Engine software. I would test the hydrometer in water and a known sugar solution to test its accuracy. If it is as you say 1 degree out you can factor that in or just buy another one. I have to say I don't worry particularly about readings until I get close to FG. For that I use a final gravity hydrometer in 1 degree graduations, similar to the one Aleman mentions.
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Re: Hydrometer vs Refractometer for OG

Post by Aleman » Mon Oct 16, 2017 10:01 am

orlando wrote:
Mon Oct 16, 2017 9:49 am
I have to say I don't worry particularly about readings until I get close to FG. For that I use a final gravity hydrometer in 1 degree graduations, similar to the one Aleman mentions.
I think mine is 0.5 degree graduations. :D

Yes, the fudge factor does depend a lot on the wort composition, but that applies to the Starting gravity as well.

JonA

Re: Hydrometer vs Refractometer for OG

Post by JonA » Mon Oct 16, 2017 10:52 am

Not long got back from hols with my Hanna 96841 in my suitcase so I thought I'd take it round to my mate who's got similar calibrated hydrometers they use for doing the HMCE duty calculations. This refractometer gives you a degrees Plato reading so you can do a direct conversion to SG.

Have to say we were both impressed with it, we tried it on various wort samples and the difference from the hydrometer was less than 1deg of sg every time.
Last edited by JonA on Wed Oct 18, 2017 4:44 pm, edited 1 time in total.

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Re: Hydrometer vs Refractometer for OG

Post by f00b4r » Mon Oct 16, 2017 5:36 pm

Aleman wrote:With a decent correction formula the refractometer. ;) Look Up Sean Terrils work ;)

I still use both, but I do have a nice 0.990 - 1.020 hydrometer for finishing gravity readings

After reading you mention this in a thread from a while ago and reading the stuff on his site I have been using the Refracto iOS app set to use the Terril cubic factor calculations, it has always been within one point or ageing with my hydrometer and my precision finishing hydrometer, it even lets you set a wort correction factor (not that I seen to have needed this for my standard beers). It definitely makes life a lot easier.

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To the op, ensure you do not use a refractometer that "shows" gravity points as they will likely not be an accurate representation of the relationship between that and brix.

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Re: Hydrometer vs Refractometer for OG

Post by MTW » Mon Oct 16, 2017 5:58 pm

The hydrometer; a refractometer is a problem for a solution to me, except on the fly for runnings and a rough pre-boil SG
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Re: Hydrometer vs Refractometer for OG

Post by chefgage » Mon Oct 16, 2017 6:23 pm

I tried getting on with a refractometer but could never get it to read anything like what my hydrometer does, it seems to have a mind of its own :):)

I spent ages making up various dme solutions to test it but to no avail. Went back to just using the hydrometer.

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Re: Hydrometer vs Refractometer for OG

Post by WalesAles » Mon Oct 16, 2017 9:37 pm

OMG! #-o
Do I really want / need a Refractometer. Of course I do. It is another bit of Kit in the Beer Shed #-o
For the time being I will just keep sticking my finger in the Beer, smell it, taste it then bottle it! :D

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Re: Hydrometer vs Refractometer for OG

Post by alexlark » Tue Oct 17, 2017 7:57 am

I had one when I kept marines so was used to using one. Nice and quick when taking an OG.

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Re: Hydrometer vs Refractometer for OG

Post by tourer » Tue Oct 17, 2017 7:26 pm

Refractor for the OG and Hydrometer for SG because OG wort is not nice to sample/drink but SG is, so i use both. Also you'll throw away OG sample (about 1/2 pint?) but drink the SG :D

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Re: Hydrometer vs Refractometer for OG

Post by chefgage » Tue Oct 17, 2017 7:40 pm

tourer wrote:
Tue Oct 17, 2017 7:26 pm
Refractor for the OG and Hydrometer for SG because OG wort is not nice to sample/drink but SG is, so i use both. Also you'll throw away OG sample (about 1/2 pint?) but drink the SG :D
I like to drink both :) especially a nice hot wort sample :)

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Re: Hydrometer vs Refractometer for OG

Post by alexlark » Wed Oct 18, 2017 6:22 am

tourer wrote:Refractor for the OG and Hydrometer for SG because OG wort is not nice to sample/drink but SG is, so i use both. Also you'll throw away OG sample (about 1/2 pint?) but drink the SG :D
What he said.

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