Brix to SG is not that simple

I have just spent an hour googling this topic. I found many tables, most of them significantly different from one another. Primetab looks a good source, itself referencing the handbook of chemistry and physics, but is based on sucrose solution. Beer wort is mainly maltose, I believe. So, folks, can we come to any consensus on the most accurate conversion available, that takes into account increasing alcohol and decreasing maltose as the wort ferments.

I don't think you will find a conversion table based on maltose alone, but those based on sucrose should be close enough for brewing purposes. The difference would probably be very slight. I don't think there is a conversion table for an alcohol/maltose blend. There are formulas that will approximate the specific gravity of a fermenting solution using a refractometer reading and a hygrometer reading together. Some brewing software (such as ProMash) has a utility that you can use in lieu of punching out the numbers manually.

IMO, there is no need to go to all that trouble. Most of the time you will want to use the refractometer to determine the approximate gravity pre & post boil so that you can maybe adjust your volume to get the desired target gravity and maybe determine your efficiency. After that, most of us just use a hygrometer to check the OG prior to pitching the yeast and to get a more precise number than you can get from a refractometer. A hygrometer is typically then used again to check the final gravity. A refractometer is certainly a great tool, but you still need a hygrometer.

Here's a USDA conversion table that I sometimes use. Most of the time I just mulitply the Brix reading times 4 to get an approximation:

http://www.greenwoodassociates.com/ref/Detailed Brix Chart.pdf

many thanks, mate, I need to know the ABV as accurate as possible hence the question, I only have a refractometer.

note the typo 12 brix = 1.480 - smiles

I have been using http://www.onebeer.net/refractometer.shtml to convert brix to gravity.

if you have an accurate weigh scale you can take a filtered (or clean) sample of your beer and dry it out to determine %sugar. If you know your OG you can then determine ABV. It's a long way around but it has always worked for me.

the onebeer.net reference is quite different to what I am using....

Catt22 said:

After that, most of us just use a hygrometer to check the OG prior to pitching the yeast and to get a more precise number than you can get from a refractometer. A hygrometer is typically then used again to check the final gravity. A

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Why are you measuring the relative humidity of your wort?