The prettiest fermentation vessel I ever owned was a glazed stoneware crock with a spigot, bought at a craft fair from a potter who told me it was food safe and meant it. I brewed two batches in it before a friend who works in food testing asked, mildly, whether I knew what the glaze was made of. Neither of us did. The crock holds wooden spoons on my counter now, and everything I ferment goes into glass, because a kombucha vessel asks something of a container that a mixing bowl never does.
Why the container matters more here than in beer
A beer fermenter holds a nearly neutral liquid for a few weeks and then gets emptied. A kombucha vessel holds a mildly acidic liquid week after week, and in a continuous-brew setup it never really empties. Finished kombucha lands below pH 4.2 — that acidity is the point, and it is also a slow, patient solvent working on whatever it touches. Kombucha asks what a material will give up to its contents more insistently than anything else in a home kitchen.
That reframes the decision. It is not about volume or looks; it is about which surfaces you want in long contact with a weak acid, at room temperature, for years.
Glass is the boring, correct default
A wide-mouth glass jar is unreactive, easy to inspect, cheap, and sold everywhere in one and two gallon sizes. No glaze to worry about, no seams hiding residue, and you can watch the pellicle form without lifting the cloth. Ordinary soda-lime glass is fine; borosilicate matters only if you pour boiling tea straight into the jar instead of cooling it first.
Two exceptions. Antique or decorative leaded crystal is the wrong material for a week-long acid soak, however handsome the decanter. And a jar with a chip or crack is done — a chipped rim sheds into the cloth cover, and a cracked gallon jar carried across a kitchen is a bad afternoon.
The crock problem, in the FDA's own words
Glazed ceramic is where the real risk sits, because earthenware is porous and has to be glazed to hold liquid at all, and lead has historically been part of what makes a glaze melt and flow. The FDA's questions and answers on lead-glazed traditional pottery lays out the mechanism plainly: fired correctly, essentially all the lead is bound into the glaze and any migration is insignificant; fired improperly, the lead may not fuse and can contaminate food.
The same page names the categories consumers should be wary of, and it reads like a description of half the artisan kombucha crocks on the internet: pottery that is handmade with a crude appearance or irregular shape, antique, damaged or excessively worn, bought from flea markets or street vendors, or brightly decorated in orange, red, or yellow, since lead is often used with those pigments. Its advice for anything on that list is to test the piece with a hardware-store lead swab, and if you cannot test it or establish that it came from a reliable manufacturer, to consider not using it for food or drink at all. It also settles a hope I have seen expressed on forums more than once: no amount of washing, boiling, or other process can remove lead from pottery.
What those lead limits are measured with
Here is the detail that moved me from caution to a firm rule. The compliance guide the FDA uses for ceramic foodware sets leachable-lead action levels by vessel type, and the strictest apply to cups, mugs, and pitchers — pitchers being defined as vessels used for storing and dispensing juices or other acidic beverages. The numbers are tightest exactly where acid sits against glaze.
The test behind those numbers is ASTM C738, which leaches the ware in 4 percent acetic acid for 24 hours at room temperature. The standard describes that as a deliberately severe procedure, unlikely to be matched by real-world use — and it is, for a dinner plate. A kombucha vessel is the one household item that comes close: dilute acid, room temperature, one to two weeks per batch, refilled indefinitely. If a crock is going to give anything up, this is the application that will find out.
None of which makes ceramic forbidden. It makes it a material you buy from a maker who publishes lead and cadmium results for their glazes, or not at all. Vagueness at the point of sale is the disqualifier, not the clay.
Spigots, where the metal question really lives
Continuous brewers spend a long time choosing a vessel and about four seconds choosing the tap screwed into it, which is backwards. A spigot is in permanent contact with acidic liquid, and unlike the vessel wall it has threads, a barrel, and a seat where liquid lingers between pours. Plain polypropylene or nylon taps are cheap, inert enough, and serviceable; stainless in 304 or 316 is the nicer option.
What I avoid is brass and chrome-plated brass, common on decorative beverage dispensers. Brass has traditionally contained lead, plating wears through where a valve moves, and this is the one component that is metal, permanently wetted, and hidden from view all at once. Whatever the tap is made of, buy one you can take apart — a spigot you cannot disassemble is a spigot you cannot actually clean, and a sour, cloudy trickle from the tap while the jar above it tastes fine is almost always the tap's fault.
Stainless, aluminum, and the metal-kills-the-culture myth
The old advice that metal must never touch a kombucha culture is overstated, and it hides the real distinction. Brief contact with a stainless spoon or funnel does nothing measurable; food-grade stainless is what commercial fermenters are made of. Reactive metals in long contact are the actual problem: aluminum, copper, cast iron, galvanized steel, and unlined tinware all corrode in acid, and corrosion means metal moving into the drink.
So: stainless for tools and taps, no aluminum stock pot for holding sweet tea overnight, and no clamped metal lid on a fermenting jar for a second reason entirely — sealing the vessel traps carbon dioxide, which pushes the batch in a direction I have written about in the alcohol numbers for a home batch. Cloth and a rubber band, always.
Where plastic earns its place
Food-grade plastic is a trade rather than a compromise. High-density polyethylene and polypropylene handle acid fine and are what most large fermentation buckets are made of, so a five-gallon batch in plastic is perfectly reasonable. The costs: plastic scratches, scratches hold residue, and plastic picks up flavors from heavily spiced second ferments. Under three gallons glass wins on inspection and cleaning; above that, plastic starts making sense on weight and price.
Mouth, headspace, and how the jar is shaped
The culture works at the surface, so a wide, shallow vessel establishes a pellicle faster than a tall narrow one of the same volume. A mouth you can get a whole hand into beats every other feature, because harvesting a pellicle out of a carboy neck is a miserable job. Leave a couple of inches of headspace under the cloth, and between two vessels of the same size take the one with the simplest lid arrangement — fewer parts between the culture and a clean cloth means fewer things to sanitize.
The two vessels on my shelf
A one-gallon wide-mouth glass jar for batch brewing, with a tight-woven cotton square and a rubber band, and a two and a half gallon glass jar with a stainless tap for the continuous vessel — both bought for less than the crock cost. Between batches they get hot water, a soft cloth, no soap, and a rinse with finished kombucha rather than a sanitizer, since anything that kills bacteria kills the culture too. Which of the two you want is a question about your kitchen rather than your gear, and I have laid out that comparison in batch versus continuous brewing. The material question, though, has a short answer: buy glass, put stainless or plastic on the tap, and keep the handsome crock for the spoons.