# What to trust? Refractometer or Hydrometer



## Trevandjo (6/3/15)

I've got a new Keg King refractometer. I've used it on my current brew which has been in the fermenter for 10 days. The sg is 1.024 which is very sluggish to me (using Notto) so I compared it to my hydrometer which read 1.013. 

I thought "Ah! my refractometer hasn't been calibrated" so I did a cal with de-mineralised water but it came up as 1.000 at 20 deg. Also checked the same water with my hydrometer which also came up as 1.000 at 20 deg.

Any advice on which to believe? I'm tempted to buy another hydrometer to compare it to. Any other way to tell?

Thanks,

Trev


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## Liam_snorkel (6/3/15)

are you using it on fermented/ing beer? You'll need a chart.


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## Trevandjo (6/3/15)

I'm using it on a fermenting beer. Can't I use it in the place of a hydrometer? The refract reads brix and sg and also has auto temperature compensation.


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## Liam_snorkel (6/3/15)

you can, but to use a refractometer you will need to know the original SG and calculate from there. The alcohol present means you can't get a direct reading of the SG without doing a calc (or looking at a chart). A quick google search should sort you out.


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## Midnight Brew (6/3/15)

There is an app called BrixCalc which will convert the reading of fermenting wort for you. After breaking so many hydros I now only use my refract. The app also gives attenuation information.


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## Blind Dog (6/3/15)

A hydrometer measures the relative density of liquid, a refractometer measures the speed of light through a medium relative to the speed of light. Personally I've never worked out why I'd use the latter to measure the former, but that might just be me


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## Eagleburger (6/3/15)

Taste buds


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## panzerd18 (6/3/15)

Put it simply, 



Trevandjo said:


> Can't I use it in the place of a hydrometer?


Not directly. Because the alcohol in the liquid is now going to give you a different reading compared to a hydrometer reading. You can use it interchangeably when no alcohol is present.

As others suggested, you can use a refractometer in place of a hydrometer with alcohol present in the liquid, but you must use a conversion chart/calculator to get the real final gravity that will match your hydrometer reading.


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## Trevandjo (6/3/15)

Thanks for opening my eyes - yet again.

I've got a grainfather and taking the pre-boil gravity is a PITA with a hydrometer so I'll keep the refractometer for that part of my brewing until I can educate myself with the calculations.

Once again, thanks everyone who replied.

Trev


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## warra48 (6/3/15)

Here's the chart you need.


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## antiphile (6/3/15)

Hi Trev. How's Jo?

Another way of using the refractometer in a fermenting brew is to plug the figures into this formula:

Formula for compensation of ethanol effect on refractometer:

SG=1.001843-0.002318474(OB)-0.000007775(OB^2)-0.000000034(OB^3)+0.00574(AB) +0.00003344(AB^2)+0.000000086(AB^3)

where SG = Specific Gravity, OB = Original Brix, AB = Actual Brix (Brix Readings During Fermentation)

Obviously it's much easier in a spreadsheet, and this is my simple excel spreadsheet I keep for every individual batch.

Notes:

1. There are 2 compulsory inputs viz., the brew name or code or both in the first large box, and the date of the brew (or more accurately, the date of pitching for no-chillers).
2. If both hydrometer and refractometer readings are done for any day, the hydrometer reading takes precedence. The only daily input required is Day 0 (ie. OG) though FG is also recommended obviously. any others are your choice.


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## Trevandjo (6/3/15)

antiphile said:


> Hi Trev. How's Jo?
> 
> Another way of using the refractometer in a fermenting brew is to plug the figures into this formula:
> 
> ...


Jo is off overseas for 3 months and is leaving me with the kids and my brewery - thanks for asking.

I'll give your formula a crack as well.


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## takai (6/3/15)

Blind Dog said:


> A hydrometer measures the relative density of liquid, a refractometer measures the speed of light through a medium relative to the speed of light. Personally I've never worked out why I'd use the latter to measure the former, but that might just be me


Because it is much easier to let 1-2mL of wort to cool than 100mL.

Refractometers are invaluable in the making process, but mine goes back in the box once the yeast is pitched.


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## jhsbaker (6/3/15)

:beer: to refractometer during fermenting. Hydrometer wastes too much beer. As long as you take a reading prior to ferment the refractometer is good enough for our purposes. I have checked it a few times against hydrometer for finished beer and they are pretty close. Only problem is for dark beers sometimes the line is a bit blurry - does anyone else get this problem?


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## Mr B (9/3/15)

When you calibrate a temp compensating refractometer, do you need to do it at e.g. 20 deg?


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## warra48 (9/3/15)

Temperature compensating means just that.
Just calibrate it at your ambient temperature. Works fine for me. I only need to adjust mine very slightly maybe 2 to 3 times a year.


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## fletcher (9/3/15)

James said:


> :beer: to refractometer during fermenting. Hydrometer wastes too much beer. As long as you take a reading prior to ferment the refractometer is good enough for our purposes. I have checked it a few times against hydrometer for finished beer and they are pretty close. Only problem is for dark beers sometimes the line is a bit blurry - does anyone else get this problem?


wastes beer? you don't drink your samples?


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## The Giant (28/11/15)

Great post guys. I was just about to ask this exact question when brewing with my refractometer for the first time. 

I bloody pitched another yeast and everything thinking it had stalled at a brix of 7!! Now I know!


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## Dave70 (28/11/15)

James said:


> :beer: to refractometer during fermenting. *Hydrometer wastes too much beer. * As long as you take a reading prior to ferment the refractometer is good enough for our purposes. I have checked it a few times against hydrometer for finished beer and they are pretty close. Only problem is for dark beers sometimes the line is a bit blurry - does anyone else get this problem?


I allow for this in the 'losses to trub and chiller' field of Brewmate. Or not. Cant say I notice a cup full of beer in the scheme of things,


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## Matt (28/11/15)

Here's the calculator I use. Sean has done some heavy maths to work out a refrac formula accurate enough for me to ditch the hydrometer altogether, pre- and post-pitching.


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## blotto (29/11/15)

The Giant said:


> Great post guys. I was just about to ask this exact question when brewing with my refractometer for the first time.
> 
> I bloody pitched another yeast and everything thinking it had stalled at a brix of 7!! Now I know!


That's exactly what I did! Now like others I just use the refractometer before I pitch the yeast. Plus I had trouble in the past getting two readings the same with the refractometer so I went off it a bit.


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## Mr B (21/12/15)

warra48 said:


> Temperature compensating means just that.
> Just calibrate it at your ambient temperature. Works fine for me. I only need to adjust mine very slightly maybe 2 to 3 times a year.


Hmm, I do mine every time I use it. Have to adjust it most times. Its the standard $45 one, cant remember which store I got it from.

My latest theory is that it depends on ambient temp, but not really sure.

I cube, and generally the cubes measure a couple of points over the measurement at the end of boil on brew day (sample cooled to ambient or a bit above)


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