Kefir Lifter-Strainer for Mason Jars

A rethought strainer design for daily home kefir brewing. Pour milk in, let it ferment, then lift the whole insert out — your grains stay in the cylinder, the finished kefir stays in the jar. No pouring through a mesh, no lost grains, no mess on the counter.

Why V2

The original version had a flange at the top that rested on the jar opening. It worked, but mason jar dimensions vary between brands, and a flange large enough to fit most of them was also hard to print cleanly without supports.

V2 solves two things at once:

Universal fit. The cylinder no longer rests on the jar rim. Only the handle sits above the jar, so any jar with an opening around 75mm works — no flange dimension to get right. A paper towel with a small slit for the handle covers the jar opening, keeping out dust and fruit flies during fermentation.

Better contact between milk and grains. In V1, grains packed in the center of the cylinder had limited contact with the milk — fermentation depended on lactose slowly diffusing inward through the grain mass. A thin, flat basket with large surface area would solve this, but wouldn't fit a round jar opening. V2 wraps that thin-walled geometry into a coaxial double-cylinder: an outer perforated wall, an inner perforated wall, and a perforated base ring connecting them. Milk flows freely through both walls and the base, so every grain stays in contact with fresh milk. The grain mass is effectively "unrolled" into a thin shell that happens to be cylindrical.

How it works — daily routine

1. Drop the grains into the annular space between the two walls

2. Place the strainer in a mason jar (~75mm opening)

3. Pour fresh milk into the jar — it flows through the perforations and surrounds the grains

4. Cover with a paper towel, slit for the handle

5. Ferment at room temperature for ~24 hours

6. Lift the strainer out by the handle — finished kefir stays in the jar, grains stay in the strainer, ready for the next batch

That's it. No straining, no scooping, no funnel.

Two sizes

Two cylinder diameters are included:

- Standard — for personal or couple use

- Large — for families who go through more kefir

Both use the same handle.

The handle

Printed separately and snaps into the inner cylinder: pinch the two clip legs together between your fingers, slide them into the holes at the top of the inner tube, and release. The clips lock it in place. Pinch again to remove.

The row of holes along the handle is for an optional support skewer (see below) and doubles as a grip.

Setting the depth — skewer support

The handle has a row of holes along its length. Pass a bamboo skewer through one of them and rest the skewer across the jar opening — the cylinder hangs at whatever depth that hole sets.

This matters most in tall jars. If your jar is much taller than the cylinder, don't let the strainer drop to the bottom: pick the hole that keeps the open top of the cylinder just above the milk line. Grains float at the start of fermentation, and this keeps them inside the annular space where they belong.

The same trick is useful for thick batches — when the kefir has set and you want the cylinder suspended rather than sitting on the bottom, or partially lifted out of the kefir while transferring between jars.

For a jar close to the cylinder height, you don't need the skewer at all — the strainer simply sits in the jar.

Maintenance

Grains grow and multiply. Every two to four weeks I remove them from the cylinder, rinse them quickly under cool, filtered water (tap water contains chlorine/chloramine, which can damage the culture), separate the excess, and share the extras with friends. Then back into the strainer for the next batch.

A quick rinse of the printed parts with cool water and a soft brush between full cleanings is enough for daily use. For a deeper clean, soak in a vinegar solution, then rinse thoroughly.

Print Settings

- 0.4mm nozzle — steel nozzle strongly recommended (no brass contamination)

- 0.2mm layer height (0.12–0.16mm gives smoother perforation walls if you prefer)

- No supports required

- Food-safe certified PETG filament only

- Print on a clean, residue-free build plate

- Printed on a Prusa MK4

Food Safety Notes

I use PETG filament certified food-safe and a steel nozzle to avoid any metal leaching. The geometry is designed without narrow crevices where biofilm could build up — the perforations are through-holes, not pockets, and the double-wall layout flushes cleanly under running water.

FDM-printed parts do have layer lines, and some people prefer not to use them with food for that reason. If that's a concern for you, this isn't the project for you — and that's fine. For daily kefir use with a proper rinse routine, I've had no issues.

Files

- V2 strainer — standard size

- V2 strainer — large size

- V2 handle (prints separately, snaps in)

- V1 original (kept for reference)

Links

Food-safe PETG filament I use: https://www.amazon.com/dp/B0BBBHMGKY