TRIAL JAR

A hydrometer trial jar (also called a test jar) is a tall, narrow cylinder used to hold a liquid sample so you can measure its density with a hydrometer.

Why use a trial jar instead of a bucket?

While you could technically float a hydrometer in your large fermentation tank, using a trial jar is the industry standard for three main reasons:

Sanitation: It is much safer to pull a small sample out than to risk dropping a glass instrument into your entire batch of wine.
Precision: It allows you to bring the sample to eye level. To get an accurate reading, you need to see exactly where the liquid meets the scale (the meniscus).
Efficiency: It requires very little liquid to float the hydrometer, so you don’t waste much of your “precious cargo.“

Key Features

Material: Made from food-grade plastic.
Design: Wide base to prevent tipping and a pour spout at the top.
Volume: Holds 100ml —just enough for a standard hydrometer to float without touching the bottom or sides.
Graduations: Has graduated markings up to 100ml so accurate samples can be taken.

How to Use It Correctly

The Fill: Fill the jar about 3/4 full. You want enough liquid to float the hydrometer, but not so much that it overflows when you drop the instrument in.
The Spin: Give the hydrometer a gentle spin as you lower it. This dislodges any tiny air bubbles clinging to the glass, which could otherwise “lift” the hydrometer and give you a false high reading.
The Temperature: Most hydrometers are calibrated to 20°C (68°F). If your sample is much hotter or colder, you’ll need to use a correction chart.