Equipment

Glass demijohns and carboys

Is a glass demijohn a good vessel for making cider?

In short

A demijohn is a narrow-necked glass vessel, most commonly of one, five, ten or twenty-five litres, closed with a bored bung and an airlock. It contributes nothing to the cider, admits no oxygen, and shows the maker exactly what is happening inside.

For anyone learning, that transparency is worth a great deal: the progress of a ferment, the depth of the lees, the clarity of the racked cider and the first sign of a surface film are all directly visible.

The limits are physical. Full glass is heavy, glass breaks, and the narrow neck that makes it easy to seal makes it awkward to clean and impossible to reach into.

Why glass performs so well

Glass is chemically inert to everything in cider, absorbs nothing, releases nothing and carries no history from a previous fill. Its oxygen permeability is effectively zero, so the only oxygen a demijohn admits is what comes through the bung and airlock or what is dissolved during transfer. For long maturation at small scale nothing else is as good.

It is also genuinely cleanable. A smooth, non-porous, non-scratching surface holds no biofilm, tolerates hot water and tolerates every common cleaning and sanitising chemistry. The practical difficulty is access, not the material: a long-handled brush and a soak reach what a hand cannot.

Transparency is a double property. It lets the maker see the ferment, and it lets light reach the cider. Cider exposed to light — sunlight, and fluorescent light too — can develop light-induced off-aromas, so a demijohn belongs in a cupboard or under a cover during maturation even though it is tempting to keep it on display.

Headspace and the two-vessel problem

A demijohn should be filled to the shoulder during primary fermentation, leaving room for the foam, and then filled to the neck after the first racking so that almost no air sits above the cider. The trouble is arithmetic: racking off the lees loses volume, so a demijohn that was full before racking is not full after it.

The standard answers are to keep a smaller vessel for the remainder, to top up with a similar cider, or to displace the headspace with carbon dioxide. Topping up with water dilutes and is a last resort. Leaving several centimetres of air in a demijohn for six months is how a beginner’s cider becomes vinegary.

Some makers use a smaller batch deliberately for this reason: fermenting in a five-litre and racking into a three-litre and a one-litre is less elegant than a single vessel but keeps everything full.

Handling glass safely

A full twenty-five litre glass carboy weighs upwards of thirty kilograms and has no handle worth the name. Glass carboys have broken while being lifted by the neck and caused serious lacerations. Move them in a crate or a purpose-made carrier, never by the neck alone; never lift one that has been standing on a cold floor by grabbing it warm-handed; and never seal one with a solid bung during an active ferment.

Where glass stops making sense

The crossover point is usually reached at around twenty-five litres, where a full vessel becomes a two-person lift and the risk of breakage while handling starts to dominate. Above that, most makers move to food-grade plastic for fermentation and to stainless or a small cask for maturation.

A common intermediate arrangement is to ferment in a plastic vessel with a wide opening — easy to fill, easy to clean, easy to move when empty — and to rack into glass for the long, quiet part where oxygen and inertness matter most. That plays to the strengths of both materials.

Also answered on this page

Questions this page covers, so you can tell at a glance whether it is the one you want.

What size demijohn for cider?
Should I ferment cider in glass or plastic?
How full should a demijohn be?

What people ask next

Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.

Can i ferment cider in a plastic barrel, and how do i know it is safe — Plastic fermenters are usually high-density polyethylene, polypropylene or, for carboys, polyethylene terephthalate. All three are used throughout the food industry and none of them are a problem in themselves.
What equipment do i actually need to make cider at home — At kitchen scale, most people start with bought juice and a demijohn, because that removes the two hardest problems — milling and pressing — and leaves the fermentation to be learned on its own.
Can you fix a cider that has gone vinegary — Not really. Volatile acidity cannot be removed at small scale, and blending it away only dilutes it. The realistic options are to accept it, to blend a lightly affected batch into a much larger sound one, or to let it finish becoming vinegar.
Do i need an airlock, and what does it actually do
What is racking in cider making — Racking is siphoning cider off the sediment it has thrown into a clean vessel, leaving the lees behind. It clarifies the cider and, in traditional practice, is also used to slow a ferment by removing yeast with the lees.
What should i ferment cider in — Anything inert, cleanable and closable: glass demijohns, food-grade plastic, stainless steel, or a wooden cask if you can keep it sound. Vessel shape and material change how much oxygen the cider sees and how fast it clears.

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.
The Science of Cidermaking and associated technical writing
Andrew Lea · reference work · passage verified 2026-08-24
Written by a food chemist who worked at Long Ashton on apple phenolics. Unusual among specialist cider writing in that it is primary-research-adjacent: the author is describing work he did, and cites the literature. This is why it is registered at tier 1 for chemistry while a general cider book is not.

Where to go next

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