Product review

What’s included: Eight black 38 mm screw caps, each fitted with a removable poly-seal (polypropylene) gasket for an airtight closure.

Materials and design: The caps are molded from durable plastic and include a removable polyseal liner that snaps out for thorough hand washing. The gasket provides a flexible sealing surface while the rigid cap threads onto a standard 38 mm neck.

Size and compatibility: Designed for bottles with a 38 mm opening. They are commonly found on many commercial kombucha bottles and are the same size used on a variety of growlers and carboys. While not every bottled product uses a single universal neck, 38 mm is one of the most frequently encountered diameters.

How they’re used: Primarily intended to trap carbonation during secondary fermentation of kombucha, water kefir, cider, beer, mead, and seltzer. They also work for everyday bottling and storage—cold brew, oils, vinegar, iced tea, juice, and other liquids that benefit from a secure cap.

Care and reusability: Built for repeated use, these caps help reduce single-use waste. The liners can be popped out for cleaning and should be washed thoroughly after each batch. Inspect caps for cracks or wear before reusing to maintain a good seal.

Pros

Removable poly-seal liners for easy cleaning
Reusable, durable plastic construction
Good at retaining carbonation when fitted properly

Cons

May not seal perfectly on every bottle neck
Some users report cracking after repeated tightening
Liquid can collect between liner and cap if not cleaned

VerdictThese 38 mm screw lids come as a practical set for home brewers who need a reliable airtight closure for secondary fermentation and general beverage storage. They include removable poly-seal liners and are made from sturdy plastic, making them reusable and simple to clean. Performance varies by bottle neck and tightening technique, but when seated correctly they hold carbonation well and cut down

Reviews

Linda Prince 5/5

Seals well, reusable

These caps seal tightly and can be reused several times. They trap a nice amount of fizz—open with caution.
Zebra 5/5

Better than factory caps

I swapped these in for the original bottle caps. They seal more reliably and the removable liner is handy for cleaning.
I. Reid 1/5

Fail to hold air in some cases

Several of my caps leaked, so they didn’t form an airtight seal. Very disappointing.
Wendy 5/5

Perfect fit for my batches

Solid lids and a snug fit. I brew a lot of kombucha and these have worked flawlessly for me.
Lisa Will 5/5

Essential for reusing commercial bottles

These are very helpful when making homemade kombucha and reusing commercially bottled containers. They reduce the chance of an explosive, fizzy opening.
Joy Shaffer 3/5

Plastic can become brittle

After a handful of uses some caps developed cracks when tightened down to seal during fermentation.
HOB in the woods 5/5

Noticeably tighter carbonation

I reordered these lids and compared them to the originals on reused GTs bottles. The bottles capped with these held far more fizz using the same recipe and handling. A little liquid can sit between the rigid cap and the flexible liner, so I’ll be rinsing liners carefully to avoid tossing them out. Overall very pleased with the company’s brewing gear.