April 21, 2026
Description
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.
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.
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 cylinder diameters are included:
- Standard — for personal or couple use
- Large — for families who go through more kefir
Both use the same 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.
At the start of fermentation, fresh grains are light and the whole cylinder floats near the surface. As the kefir thickens, the grains grow heavier and the cylinder can sink until it touches the jar bottom — not a problem, but sometimes you want it suspended at a specific depth instead (for example, when transferring a thick batch between jars, or when you want to leave the cylinder partially out of the kefir).
For that case, pass a bamboo skewer through one of the holes in the handle and rest the skewer across the jar opening. The cylinder hangs from that skewer at whatever depth the hole index sets.
This is optional — most daily brewing doesn't need it.
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.
- 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
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.
- V2 strainer — standard size
- V2 strainer — large size
- V2 handle (prints separately, snaps in)
- V1 original (kept for reference)
Food-safe PETG filament I use: https://www.amazon.com/dp/B0BBBHMGKY
License:
Creative Commons — Attribution
danec
