The density check, step by step

Check the instrument before the season

A hydrometer can be checked in water, which should read where the scale says water reads at that temperature. A refractometer is zeroed on distilled water. Neither takes long and both catch an instrument that has quietly been wrong, which is the failure that contaminates a whole season of readings rather than one batch.

Fill the cup properly

Enough syrup that the hydrometer floats free without touching the sides or the bottom, poured rather than dripped so it is not full of bubbles. A hydrometer resting against the cup reads high, and bubbles on the stem read low.

Match the mark to the temperature

Syrup hydrometers carry a hot test and a cold test mark, and they are not interchangeable. Decide which one this reading is, know roughly what temperature the sample is at, and use the matching mark. Reading hot syrup against the cold mark is the classic way to finish a batch at the wrong density while doing everything else correctly.

Read at eye level, on a settled sample

Look across the surface rather than down at it, and let the sample settle first. A reading taken in a hurry on a cloudy or foaming sample is a number about that moment rather than about the batch.

Record five things

The reading, the temperature, the instrument and mark, the batch code and the date. Those five together are evidence. The reading on its own is a number nobody can interpret later, including you.

If it is outside the window

Correct the batch and measure again rather than deciding the instrument is wrong. Below the floor, keep evaporating; above the ceiling, thin it with a lighter batch or water and re-measure. What you do not do is record the reading you wanted.

References