Hydrometer / Promash query

[ano]

I didn't want to risk filling the excellent how to with potential mis-information so thought I'd ask here.

I buy a magazine called wired (think Arthur C Clarke meets GQ) and in the latest issue it takes a look at some of Africa's beers. In an effort to make sure you're getting what you pay for it then outlines a method for establishing the alcoholic content of what's in the bottle. This is a quote:

Theory

... A refractometer finds the amount of sugar in a solution by measuring how much light bends as it passes through it. This is expressed in Brix, the ratio of the mass of dissolved sugar to water. With this reading, coupled with the hydrometer's FG reading, we could calculate the beer's OG and therefore the alcohol by volume with ProMash.

Method

First calibrate your refractometer. Put drops of distilled water on the lens and close the plate, checking the lens is totally covered, with no air bubbles. Leave for 30 seconds. Look through the eyepiece and adjust the instrument to focus on the scale. Now move the calibration screw until the reading is zero. Dry thoroughly with a soft cloth.
Warm the beer to 20C, the temperature to which the instruments are calibrated. Put a few drops on the refractometer lens, remove the bubbles and take a reading. Pour 10cm of beer into your sample jar, angling the tube to avoid froth. Lower your hydrometer into the beer until it floats and spin it to remove bubbles. Take a reading at the surface of theer, ignoring the meniscus. Load ProMash and click "%Alc". Type in your two readings and ProMash will give you both ABV and OG

A number of questions from me before I start emailing the editor (exams are over see):

1) Why the need for the hydrometer? I thought a refractometer's Brix could be converted to brewer's degrees?

2) Are refractometers temperature independent? I thought you had to get a specific temperature correcting model?

3) Ignore the meniscus? Does this mean from the bottom of the meniscus as I was taught all those years ago? (like the how to) ie is the meniscus the bit that runs up the side?

4) If you know how much sugar is in solution now it surely doesn't help you accurately calculate the amount of sugar there was unless you know the attenuation of the yeast used, or am I missing something?

I don't have ProMash which doesn't help.

Cheers.

 

[Vossy1]

Hi ano,

Try the free evaluation version of ProMash here

 

[Aleman]

The method works completely.

The refractometer cannot be used to determine the 'correct' FG of the beer as ethanol (alcohol) also has a refractive index, and this throws off the reading . . . The only time a refractomer is correct is before the yeast is pitched . . . . If you know the OG (converted from a brix reading if necessary) then at any stage of fermentation you can take another brix reading and derive the 'true' current gravity with an awfully complex bit of maths. . . . this is the reason for the hydrometer.

Refractometers are more or less temperature independant but are still calibrated to work accurately at 20C . . . an ATC model compensates for the ambient temperature of the instument . . . NOT the sample.

'ignore the meniscus' . . . In other words read from the level of the liquid . . . not the top of the meniscus as described correctly in TS excelent How-To.

You do not know the amount of sugar in the solution . . the fancy mathematics in Promash (other brewing software is available) enables you to convert the sugar density as calculated by the hydrometer and the reading from the hydrometer (sugar plus alcohol) to determine more or less the ABV of the beer . . . Of course it also ignores the effect of the alcohol on the hydrometer, but it is close enough.

 

[ano]

Cheers Vossy1, I have once, not sure if it will let me again but will give it a go.

:ugeek:

oooo aahhhh. Ok.

Any brewing science books you could recommend?

 

[jamesb]

Cheers Vossy1, I have once, not sure if it will let me again but will give it a go.

:ugeek:

oooo aahhhh. Ok.

Any brewing science books you could recommend?

See your e-mail.

 

[Aleman]

Well there is Malting and Brewing science (Vol 1 and II) By Briggs, Young, Hough and Stevens . . . cheap at 190 quid .

Or Lewis and Young 'Brewing' . . . around 40 quid for the second edition

Fix - [urlhttp://www.amazon.co.uk/exec/obidos/search-handle-url?_encoding=UTF8&search-type=ss&index=books-uk&field-author=George%20J.%20Fix]Principles of Brewing Science , Analysis of Brewing Techniques[/url]

and I'm thinking of adding this one

Bamforth - Scientific Principles of Malting & Brewing

I should add that these are all aimed at Degree Level Students of brewing . . . and do not necessarily help craftbrewers :lol:

 

[ano]

Well there is Malting and Brewing science (Vol 1 and II) By Briggs, Young, Hough and Stevens . . . cheap at 190 quid .

Quite. And people wonder why students are poor heh.

Thanks for the links though, might be tempted if I go on holiday. I did Chemistry up to AS level so am familiar with bits, and sciencey stuff doesn't scare me (too much) just haven't used it in a while so am a bit slow on the uptake. All this has made me want to go back to uni and do microbiology with chemistry.