Glossary · Equipment
Trial jar
Also written test jar, hydrometer jar. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
A tall narrow cylinder in which a sample is held for a hydrometer reading, deep enough for the instrument to float clear of the base and narrow enough to need little juice.
- Subject
- Equipment
- Also written
- test jar, hydrometer jar
In more detail
The geometry is the whole of the design. A hydrometer measures the density of the liquid it displaces, so it has to float clear of the base and clear of the walls: touching either makes the reading wrong, usually high, and a beginner who takes a reading in a mug is reading the mug. A trial jar is tall enough that a standard hydrometer floats free and narrow enough that filling it costs 100 to 250 millilitres rather than a litre.
Two habits go with it and both are about not lying to yourself. Return the sample or discard it, but do not pour a sample that has been sitting open back into the ferment. And read at the bottom of the meniscus at the temperature the instrument is calibrated to, which is usually 20 °C — a reading taken on juice straight off a cold press can be several points out, and several points is the difference between a cider that will finish at 5.5 per cent and one that will finish at 6.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Equipment
Hydrometer
A weighted float whose depth of immersion indicates the density of a liquid, used to read specific gravity before and during fermentation.
Chemistry
Specific gravity
The density of a liquid relative to water at the same temperature. In cider it is the routine measure of dissolved sugar before fermentation and of progress during it.
Where to go next
- Cider glossary — The whole vocabulary, by subject and A–Z.
- Comparisons — Terms that are only really clear when set against the thing they are not.
- Search — Finds terms by their aliases and by their spellings in other languages.
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
The New Cider Maker’s Handbook: A Comprehensive Guide for Craft Producers
Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against the Open Library union catalogue: Chelsea Green Publishing, 2013, ISBN 9781603584739, one edition recorded. That establishes the citation points at a real book in a stated edition, which is what a citation needs and is all it establishes. No copy was opened and nothing is quoted from it. The book itself is in print and not digitised in any open collection; where CiderHQ needs a figure from this territory it uses an accessible research source instead and says so.