Refractometer FG Calculation

[TempTest]

Hello,

I've read that it is possible to use a refractometer reading of OG and FG to calculatate ABV. My refractometer shows brix and gravity, although my eyes ability to read it accurately let this down somewhat. The readings taken from the refactometer are:

OG: 12.0 brix, 1.046 gravity
FG: 6.2, 1.024 gravity

I've used numerous calculators:

http://www.brewersfriend.com/refractometer-calculator/
http://seanterrill.com/2012/01/06/refra ... alculator/
http://www.petedrinks.com/abv-calculato ... ydrometer/

All give different results (4.8%, 4.4%, 5.1%). Can anybody give me a reliable calculator they use before I give up and return to the hydrometer? I'm hoping to use the refractometer as in my 1 gallon batches I cannot afford the loss to hydrometer samples (and do not want to readd to the fermenter in case of infections)... The drop or two loss to a refractometer I can live with!

Any tips?

[Goulders]

First ignore the gravity scale on the refractometer as they are not accurate. 12 Brix is 1.048
Just stick to the hydrometer. If you sanitise both the hydrometer and sample jar you will be fine.
It isn't easy to use a refractometer for FG, but have you seen this thread?
viewtopic.php?f=6&t=71867

[Aleman]

I Seans formula. I find that it gives a better correlation between the FG Brix reading and an accurate hydrometer reading taken at the same time.

Of course you also have to factor in. Not only the conversion from Brix to gravity but there are 4 (at least) formulas to calculate abv and each of those gives a different reading.

[TempTest]

Thanks for the reply.

I think the 1.046 / 1.048 could easily be attributed to my inability to accurately read the device... I have to remove my glasses to use it and then it's not as sharp as I'd like! Having said that, I've played with the above three sites using various input now and even with guessing the correction factor (well, leaving it at the default compared to various extremes) I only find the ABV different by less than 6.5%... To be honest with you, so long as my ABV is within 10% of the true reading then I'm happy. On a 'standard' 4% beer that's only out by +/-0.26% and on a 'big' 10% beer +/-0.65%... I'm fine with that and can happily accept my previous hydro readings may have been out by this amount based on operator (reading) error.

I think I'll stick to the calculator at http://www.petedrinks.com/abv-calculato ... ydrometer/ ...

PS. I'll continue to take side-by-side hydro and refractometer readings when doing 5 gallon brew lengths and hopefully in time get a better feeling for the refractometer.

[alexlark]

Don't forget to turn the eye piece to bring the scale into focus.

I use my refractometer for OG only. I find it easy enough to sanitise the hydrometer and take a FG reading from the FV.

[FUBAR]

I've recently got a refactometer and have found over the last 3 brews, comparing against hydrometer readings that the Sean Terril calculator has been giving results that are as near as damn it, certainly close enough to take advantage of the ease of use of the refactometer over a hydrometer. Think my hydrometer will now join the redundant brewing items box .

[vacant]

Think my hydrometer will now join the redundant brewing items box .

You'll regret it. Drinking the contents of a trial jar is more of a treat than licking a refractometer.

[Aleman]

so long as my ABV is within 10% of the true reading then I'm happy.

How do you actually know that without having the beer analysed??

The true reading is whatever the lab abv analysis say it is.

A reading derived from brix values of a refractometer may vary from this, as will a calculation using an SG and FG hydrometer reading, because it depends on which conversion formulae (Brix -> Gravity and Gravity -> ABV) are used. A single factor abv calculator will over estimate at one end of the gravity range and under estimate at the other. The HMRC abv calculator (which is used to calculate duty payable) uses a range of gravity bands with different factors for each band to minimise this. . . . but still may or may not really reflect the actual abv value of the beer.

Don't even get me started on the reliability or accuracy of LHBS hydrometers, and the insane way they are used by home brewers. you are better off measuring gravity using a dampened finger, or let a chimpanzee with a blunt stick do it for you!

[ahnlak]

[quote="TempTest"]I think I'll stick to the calculator at http://www.petedrinks.com/abv-calculato ... ydrometer/ ...[/quote]

Thanks - that's me

Plugging in your Brix readings, mine comes in at 4.52%, which is pretty close to Sean's figure of 4.4%. I've spent far too much time exploring the many different formulae for each step and I *think* that I'm using the most accurate ones I could track down.

The HMRC abv calculator is pretty inaccurate, despite the different gravity bands.

Pete

[TempTest]

so long as my ABV is within 10% of the true reading then I'm happy.

How do you actually know that without having the beer analysed??

Okay, so '10% of whatever my hydrometer would have fooled me into believing the ABV was' - which in itself might be more than 10% of the actual reading. And if we're in the region that even the hydrometer cannot be trusted (as you go on to explain) then there is really little point over worrying if the refractometer is out any at all. Indeed, it goes to show the difference I see between the calculators is probably of a smaller margin of error than the measurement itself. It'll do for me, anyway.

Thanks - that's me

Plugging in your Brix readings, mine comes in at 4.52%, which is pretty close to Sean's figure of 4.4%. I've spent far too much time exploring the many different formulae for each step and I *think* that I'm using the most accurate ones I could track down.

The HMRC abv calculator is pretty inaccurate, despite the different gravity bands.

Pete

That's great. What I like about your calculator is that it does not give results to a ridiculous number of significant figures. If I'm only reading my refractometer to .1 brix (and probably more .2 brix, given the difficulty distinguishing between adjacent readings) then calculating a result to greater resolution than this is worthless. I do assume, however, that internally you're calculating with more decimal places? (I.e., the difference between your calculators and others is down to an equation difference rather than rounding errors). Also, I think Sean's equations are calculated from empirical data so probably will not match your 'off the shelf' (theory based, I assume) equation. I don't think that's a concern though, given that we do not have the exact same refractometer as Sean - It, like all others, still requires a calibration factor input and with the best equation in the world if it relies on you inputting a calibration factor (that might not have been calculated as rigorously as the equation driving the calculator) then all bets are off.

All things said and done, I'm not going to get too worried about working out my own correction factor. I'll stick to 1.04 and use your calculator and be done with it - Good enough for me at the moment, at least. Now I just need to make up a little cheat sheet to keep with the refractometer and I'm away!

[ahnlak]

It *mostly* calculates with more decimal places than it shows, although there are a couple of points when it rounds before it probably should - that said, in those areas it makes very little difference to the final figure.

I think i'm right in saying that the equations I'm using were built as 'best fit' to actual measurements; I did work through about a dozen different variants for every stage and tracked down the ones that seemed to give the most reliable and consistent results - although lacking a lab I can't promise to have picked the perfect ones

[DeGarre]

I am disappointed at the Signstek ATC 0-32% Beer Wort Wine Brix Refractometer Sugar Content Specific Measurement Tool I got from Amazon.
Even the OG calc is off, two different hydrometers were both showing 1046 which is 12 brix, refractometer is showing 10.8-11 which is around 1041. My old but now broken refractometer used to be dead accurate.

[vacant]

I am disappointed at the Signstek ATC 0-32% Beer Wort Wine Brix Refractometer Sugar Content Specific Measurement Tool I got from Amazon.

Have you calibrated it?

[BlackRocksBrewery]

I use the refractometer during sparging/boiling and hydrometer prior to pitching yeast. For pale ales an approximate calculator is to multiply the Brix reading x4. This is optimistic but provides very quick readings as an indication of the gravity at that stage of the brewing process and also guides when to stop sparging. This is a real time saver during the brew. I dont have a temperature compensated refractometer but this isn't a problem as the few drops of wort to be checked quickly cool down. For more accurate readings I use a hydrometer but this is only carried out when the wort is down to around 20 deg C and prior to pitching the yeast.

[DeGarre]

Not to calibrate and moan here would've been a schoolboy error...I did calibrate with distilled water which made no difference to tap water.