Refractometer

[akacake]

I didn't take a SG reading at the start so can't determine my abv. I've tried a vinometer but can't seem to get it to work. Is a refractometer a good choice to measure the abv? Are there different types I should look for?

 

[bernardsmith]

You need to know the starting gravity to be able to use a refractometer once the yeast has begun to produce alcohol. Refractometers are calibrated to be used where the liquid solution is water not alcohol so to obtain a meaningful reading the amount of alcohol in the solution needs to be factored in. Knowing what the starting gravity was and what the current reading when run through a set of formulae accounts for this. But if you know the fruit you are fermenting and the amount of water /sugar (if appropriate ) you added you can usually come up with a reasonable starting gravity(most table fruit when pressed will produce a juice at about 1.045, 1 lb of sugar adds 40 points to a gallon of water and ripe wine grapes (I believe) have a brix of about 21 or a gravity of about 1.090.

 

[Petebrewer]

I recently discovered a published method to measure the abv of a wine using hydrometer and refractometer readings. With this method you can measure the abv of a finished wine without knowing the original gravity. I used the method this year to measure the abv of a shop bought Tawny Port and a Piesporter and found the results tied in well with what was stated on the labels. I've incorporated a calculator for this is my Home Wine Program. It's free and downloadable from www.homewineprogram.com.

 

[GeneDaniels1963]

There are several online calculators for converting BRIX to abv. Here is the one I use all the time:

https://www.northernbrewer.com/learn/resources/refractometer-calculator/

 

[bernardsmith]

GeneDaniels1963, I don't think the real issue is converting brix to ABV. You multiply by 4 and that is usually close enough. The problem is how to use a refractometer in the presence of alcohol. The readings (whether brix or ABV) assume the solution is water and not ethanol. Light is refracted differently as it passes through alcohol and as the ABV of the wine/mead/beer/cider etc to be measured rises the angle of refraction changes but the scale is not measuring ABV but nominal concentrations of sugar dissolved in WATER. But now the solution is water PLUS ethanol.

 

[Petebrewer]

Bernardsmith the fact that both sugar and alcohol will refract light is the basis for the method devised by Rogerson and Symington. They are makers of Port and published their method of estimating the alcohol content of a wine or must by using measurements from a hydrometer and sugar refractometer. It can be viewed at www.ajevonline.org/content/57/4/486. The Home Wine Program includes a calculator which will also work out the level of unfermented soluble solids (which will usually be mostly sugar). Free download is from www.homewineprogram.com The reason they devised the method is so that they can recognise the point at which the fermenting Port must has reached about 8% alcohol, as that is when they want to stop the fermentation by adding brandy.

 

[bernardsmith]

No argument from me - although I am unfamiliar with the specific calculator you refer to. My point is that you need to use a calculator because you cannot simply use the reading from a refractometer when there is alcohol in the solution...