Refractometer

[Parva]

I bought an Atago N1 refractometer off of Ebay some time ago in order to aid me in measuring SG during sparging and fermenting. It covers 0 - 32% Brix. It's been laying around unused due to the readings being massively off those that I achieve with my hydrometer and I'd like to know if it's shafted or I'm just using it wrong.

I calibrated it with tap water to a zero reading. Now I know I should use distilled water to get it precise but surely the figures aren't that far different? I also ensure that there are no air bubbles trapped when I take a reading. I'm also aware that there may be some variation in the readings with refractometers but surely not as widely as I'm getting. I'll go take a reading of my fermenting brew now and demonstrate.

Calibrated to '0' again with tap water to be sure. SG taken with hydrometer is 1.018, I 'flattened' the sample to ensure there were no air bubbles and got a reading of 7.6 Brix which according to the guide I have equates to an SG of 1.031. I could understand a slight difference in the readings, especially since I have calibrated with tap water but that reading is one hell of a difference I feel.

The hydrometer reads spot on 1.000 in tap water at room temperature so I'm certain it's the refractometer that's giving dodgy readings. Is it broken or is there something I am not doing correctly?

 

[Vossy1]

What was the OG of the brew P ?

I'm not familiar with that refer but it's designed to measure coolant mixtures in machinery...not sure if it's suitable for beer.
I'm sure Aleman can shed more light on it, I'll have a nsoey later :thumb:

 

[Kingfisher]

I bought an Atago N1 refractometer off of Ebay some time ago in order to aid me in measuring SG during sparging and fermenting. It covers 0 - 32% Brix. It's been laying around unused due to the readings being massively off those that I achieve with my hydrometer and I'd like to know if it's shafted or I'm just using it wrong.quote]

P I must have the same model which was described as OK for beer. I've abandoned it for the hydrometer as well. I see that Craftbrewer in OZ is advertising an SG - Brix model.

 

[MEB]

My cheapo refractometer from ebay is spot on. If it's mid summer here I calibrate it before i use it with water drops from the lid of my kettle that i allow to cool. I calibrate it to the temp of day. No point in calibrating it to 20C if ambient temp is 28C. I love my refractometer.

I think something is afoot with yours. I'm sure Aleman will be able to shed some more light on the subject.

 

[Parva]

What was the OG of the brew P ?

The OG was 1054 though I didn't bother testing it with the refractometer at the time as I've lost confidence in its ability to give me a reliable reading. I did once try adjusting it to a known SG but on testing with tap water the line was miles below zero so I suspect the readings would vary wildly at different gravities.

It was only £15 so no huge loss but if it is knackered then I'm considering getting another hopefully working one because it's far better to get an idea of gravity during fermentation using only a teaspoon or so of wort than pouring off 100ml or so into a trial jar everytime.

 

[MEB]

I did once try adjusting it to a known SG but on testing with tap water the line was miles below zero so I suspect the readings would vary wildly at different gravities.

Tap water varies wildy. You need to calibrate it with distilled or R/O water. Collect some droplets from the lid of your kettle after it has boiled. Leave for a few moments in a dropper while you blow it. Apply a few drops to the refractometer screen and then take a reading. Whatever the ambient temp is will be the temp your refractometer will be accurate(more or less) at. There's not a lot that can 'go wrong' with a refractometer.

 

[Vossy1]

Parva, I think your conversion chart is wrong :hmm:

I've just plugged 1.054 OG, 7.6 brix FG into Beersmith's refractometer tool using fermenting wort as the medium and it's giving me a corrected FG reading of 1.015

Have you got Beersmith?

 

[Parva]

Hmmm, that's interesting. Yes, I do have (and use) Beersmith though I've never tried it for the refractometer readings. The chart I got was from a link given me by IanB. http://www.beerbarons.org/publicati...eatSheets/refractometerBrixToSGConvertion.pdf I'll go take a look at it in Beersmith, cheers.

 

[Vossy1]

It's under tools on beersmith as refractometer.
The chart you linked is for wort pre fermentation.
I changed the drop down in Beersmith to unfermented wort and it gave me 1.029.

 

[Parva]

You are indeed correct Vossey. I wasn't aware that there had to be a reference to the OG to create a reading that's in the correct ball park, I'd just assumed that I could use the chart linked to above and hey presto. I'll experiment some more with Beersmiths refractometer tool in future because tipping albeit small quantities of wort down the drain (well, my neck usually) I'd prefer to avoid if possible. Cheers. :)

 

[Aleman]

As MEB says there is very little to go wrong with a refractometer. It does help a little if you understand how they work,

When light passes through a liquid/gas, liquid/solid, gas/solid, interface it is bent, a phenomenon called refraction - You can see this looking into a clear river. You may see fish in there but if you cast a spear at them you will miss, cause refraction causes them to appear closer to the surface than they are.

Now an interesting fact is that when you dissolve a substance in water many substances either increase or decrease the refractive effect, and the amount that a pure solution of a substance bends the light is directly related to its concentration (once the refractive effect of water is removed . . . via calibration with pure water).

Now a brewers refractometer is calibrated to determine the concentration of sucrose in water . . . not maltose (Or wort . . . its not a pure solution), although the difference between the two is measurable, and, luckily for us, constant so a correction factor can be applied. what is not so lucky for us is that ethanol also has a refractive effect and works in the same direction as sucrose/maltose. What this means in practice is that as fermentation proceeds the increasing level of ethanol compensates for the decreasing level of maltose (Ok so not completely the reading does still fall but not by the amount that you would expect). This means that it is impossible to take a direct reading of fermenting wort and calculate the Gravity from it via lookup tables. You can with some fairly hairy mathematical algebra calculate the current gravity if, and only if, you knew what the original gravity was before fermentation started. Most of the current brewing programs offer these calculations built in, so could possibly considered essential . . . The evaluation version of Promash allows full access to the calculators so you don't even have to buy a copy to find a use for it.

FWIW I use my refractometer during the sparge, and to measure the OG . . . I don't tend to mess with fermenting wort so usually leave it alone unless something unusual occurs when I will take a refractometer sample . . . with my Russian Imperial Stout I was that surprised by the result that I took a hydrometer sample as well :shock: The results agreed to 2 gravity points (a 1.094 wort down to 1.028/1.026 in 36 hours).

Another FWIW is that for unfermenting wort the Brix reading times 4 is approximately the OG (To be completely accurate its about 4% less than 4 times the Brix value, but the difference is only significant on BIG beers :) )

Hope this has cleared up some confusion and not added to it

 

[Kingfisher]

Thanks A :thumb: , I've previously used the refractometer as you suggest for the sparged wort, pre boil but became completely confused when sampling work in progress. The refractometer readings were far higher than the hydrometer. So I've abandoned the former until I understood the process, which thanks to the above I'm a lot clearer on.

 

[delboy]

I use this online calc on the brewheads site to work out gravity during fermentation with a refract, seems to be in agreement with my hydrometer.

calc clicky

 

[Parva]

Cheers Aleman. I should have looked further at the tool in Beersmith but blindly went along with the printout I had which of course was for unfermented wort and was unaware of the difference between that and fermenting wort. I just figured there was a fault with the refractometer but was confused as to how that could be since there was really nothing to break. Now I know better. Oh and that's quite handy Del, cheers. :)

 

[Kingfisher]

I use this online calc on the brewheads site to work out gravity during fermentation with a refract, seems to be in agreement with my hydrometer.

calc clicky

: DB I've added it to favourites :)