Glossary · Chemistry
Specific gravity
Also written SG, relative density. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
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.
- Subject
- Chemistry
- Also written
- SG, relative density
In more detail
Apple juice typically starts between about 1.045 and 1.075, higher after sweating and in a warm season. A dry cider finishes below 1.000, because ethanol is less dense than water and pulls the reading beneath the water baseline once the sugar is gone.
The measurement is temperature-sensitive and is normally taken with a hydrometer in a trial jar, corrected to the instrument’s calibration temperature. A refractometer reads sugar directly but becomes unreliable once alcohol is present, so it is used before fermentation rather than during it.
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.
Chemistry
Brix
A scale expressing dissolved solids as grams of sucrose per hundred grams of solution. One degree Brix is approximately one per cent sugar by weight in juice.
Chemistry
Oechsle
A German must-weight scale: the number of grams by which a litre of juice exceeds the weight of a litre of water. A juice at 1.050 specific gravity reads 50 degrees Oechsle.
Chemistry
Potential alcohol
The alcoholic strength a juice would reach if all its fermentable sugar were converted, estimated from the starting gravity.
Fermentation
Attenuation
The proportion of the original sugar that fermentation has consumed, calculated from the fall in gravity from the starting to the current reading and expressed as a percentage.
Equipment
Hydrometer
A weighted float whose depth of immersion indicates the density of a liquid, used to read specific gravity before and during fermentation.
Equipment
Refractometer
An optical instrument that measures the refractive index of a drop of juice and reads it out as degrees Brix. Accurate on unfermented juice and unreliable once alcohol is present.
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.
Cornell Cider Research and Extension programme
Cornell University, School of Integrative Plant Science · university · passage verified 2026-08-24
Runs cultivar trials in New York State and publishes juice chemistry for European cider varieties grown in a North American climate — the single most useful counterweight to treating English figures as universal.