About measuring when brewing beer

As a homebrewer, it is best to choose a refractometer during mashing or boiling, as it allows you to measure quickly and with little wort. Bear in mind that your measurement during and after fermentation will no longer be correct because of the alcohol present.

You can use a hydrometer both during brewing and during and after fermentation. It has the advantage that you do not have to apply a correction when alcohol has already been formed. The disadvantage is that you need more wort for a measurement. So you can use it perfectly after fermentation, when you want to measure the final SG.

In short, use a refractometer for quick measurements during brewing and a hydrometer for accurate measurements after fermentation.

Original SG (OG) and final SG (FG)

Original SG (also called original gravity or OG) is measured before fermentation starts. This gives an indication of the amount of fermentable sugars in the wort and helps predict how much alcohol can potentially be formed.

Final SG (also called final density or FG) is measured after fermentation. This indicates how many remaining sugars are left in the beer. A lower FG means that more sugars have been converted into alcohol.

The difference between OG and FG is used to calculate the alcohol percentage.

Tip: To determine the lowest possible FG of your beer, you can carry out a lab fermentation. You do this by setting aside a small amount of wort after cooling and pitching it with an excess of active yeast. Allow the wort to ferment at a high temperature, between 27 and 30°C. Shake the wort regularly to speed up fermentation. After about 48 hours, the wort will be fully fermented. Leave it for a few more hours to let the yeast settle and then measure the lowest possible FG with a hydrometer. This will give you an indication of the maximum amount of sugars that can be fermented.

SG, Brix or °Plato?

Whichever scale you choose, the theory remains the same. You will often find different scales on your hydrometer or refractometer.

Measuring acidity (pH)

The pH level is an important parameter in brewing, as it affects the action of the enzymes during the mashing process and plays a role in the flavour stability of the beer. Too high or too low a pH can interfere with the efficiency of the enzymes, resulting in suboptimal conversion of starch to sugars. This can slow down the brewing process or affect the flavour of your beer. It is therefore essential to keep a close eye on pH, especially during mashing.