Spotless Straight Walls. Exact Peak Doubling.
Ditch the crusty curved-shoulder Mason jar and soggy painter's tape.
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Every detail of the Cosari LevainPro 900ml kit is built to eliminate the daily friction of feeding, scraping, and timing a living sourdough culture.
Traditional canning jars curve inward at the neck, trapping crusty dough where pink bacteria and mold breed. Our 8.5cm collarless straight cylinder wipes 100% clean from bottom to rim in two passes.
Wild yeast activity slows down below 20°C and turns overly acidic above 30°C. The vertical 16°C–34°C (61°F–93°F) thermometer strip reveals your starter's real glass temperature so you nail the 24°C–28°C sweet spot.
Slide the matte-black rubber tracking band to your fresh feeding line and point the arrow to the hour and day. Because the walls are straight, rising from 250ml to 500ml means an exact 2x volume double.
Slip on one of the 3 breathable woven linen bonnets for active aerobic countertop fermentation, or seal the rim with the gasketed natural bamboo lid for airtight cold retardation in the refrigerator.
Use the included 24.7cm narrow black silicone spatula to fold fresh flour and water into your starter at the bottom of the jar. With zero neck shoulder or embossed glass bumps in the way, one vertical sweep leaves the upper glass crystal clear.
Align the matte-black rubber band flush with your starter's top meniscus against the 100ml–900ml markings, set the directional marker to the current hour and day, and verify your ambient temperature on the vertical °C/°F strip.
Crown the 8.5cm mouth with a breathable beige linen cover while your levain doubles on the counter—or press on the bamboo lid (with its removable silicone ring installed) to store your mother starter in the fridge for up to two weeks.
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900ml Zero-Shoulder Graduated Glass Fermentation Cylinder with Built-In °C/°F Thermometer, Dual-Mode Linen & Bamboo Lids, Slim Jar Spatula & 3 Tracking Bands
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Why Straight-Wall Geometry Beats Mason & Tulip Jars: Curved-shoulder Mason jars and waisted tulip jars create two problems: they trap un-wipeable dough crust underneath the rim, and they distort visual volume readings. The Cosari LevainPro is formed as a true 15cm × 8.5cm straight cylinder. Whether you maintain a tiny 50g daily starter down near the 100ml line or build a 400g weekend levain peaking near 800ml, every 100ml increment represents the exact same vertical height.
Dual-Mode Airflow & The Veteran Baker's Gasket Trick: Different stages of sourdough maintenance require different airflow. During countertop builds, the 3 woven linen bonnets allow fresh oxygen in and CO2 out. During multi-day refrigerator storage, the natural bamboo lid's food-grade silicone ring creates an airtight seal so your starter never forms a dry crust or absorbs fridge odors. Want a solid dust cover on the counter? Simply slip the removable silicone gasket off the bamboo lid so it rests loosely with gentle airflow.
Materials, Dimensions & Care Instructions: Crafted from clear, distortion-free laboratory-style borosilicate glass (900ml / 30.4 fl oz graduated capacity; 15cm height × 8.5cm diameter) with a natural bamboo lid, food-grade silicone spatula (24.7cm length) and tracking bands, and unbleached woven linen covers. To keep the external liquid-crystal thermometer strip accurate for years, hand-wash the jar exterior with warm soapy water and avoid striking the glass against metal sink faucets.
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2-Year Warranty: If anything goes wrong within 2 years, we replace it free of charge or refund your order in full.
In our 80%-hydration rye test, wiping the straight walls with the included 24.7cm slim black silicone spatula took just 11 seconds—eliminating the dried wall crust where mold starts.
No more scraping your knuckles on sharp metal threads. The smooth, fire-polished 8.5cm opening lets you reach a sponge straight to the bottom crease during deep cleans.
While rival jars charge $39+ for bare glass, Cosari includes 3 linen covers, 3 rubber bands, the bamboo lid, thermometer strip, narrow spatula, 6 chalkboard labels, and the white marker.
Cosari LevainPro 900ml Straight-Wall Sourdough Vessel KitStandard Competitors
| Feature | Cosari LevainPro 900ml Straight-Wall Sourdough Vessel Kit | Standard Competitors |
|---|---|---|
| Interior Wall & Neck Geometry | 100% Straight 90° Cylinder (0mm Shoulder) | Inward-Curved Shoulder Traps Dough Crust |
| Volume & Rise Doubling Readout | Fired 100ml–900ml Marks + 3 Time/Level Bands | Blank or Embossed Glass (Requires Tape) |
| Fermentation Temperature Tracking | Built-In 16°C–34°C (61°F–93°F) Thermometer | None (Blind Room-Temp Guessing) |
| Countertop vs. Fridge Lid System | 3 Breathable Linen Covers + Airtight Bamboo Lid | Rust-Prone Tin Rings or Single Lid Only |
| Included Scraping & Labeling Tools | 24.7cm Slim Silicone Spatula + Labels + White Pen | Sold Separately ($25–$35 Extra) |
Swipe left for steps 2 and 3
Spoon your starter into the 900ml cylinder, stir in fresh flour and water, and glide the 24.7cm narrow black silicone spatula straight up the 90-degree glass walls.
Slide the matte-black rubber band flush with your starter's top line, point the arrow to your feeding hour, and check the °C/°F thermometer strip.
Cap with the breathable beige linen bonnet to watch your starter double on the counter, or seal with the gasketed bamboo lid for cold storage.
These are the best. I ordered the complete kit because I love a straight-sided jar. My small everyday starter is perfectly happy in it, and there's room to build a bigger levain up toward the 900ml mark when I need one.
The best part is that I can fit my whole hand through the wide opening and really scrub the jar. The narrow black spatula also makes it easy to keep the inside walls clean between feedings. Would order again.
Just transferred my starter into this 900ml jar today and so far I really like it. I'm using the linen cover on the counter, then I'll switch to the wooden lid with its silicone ring when it goes in the fridge.
I've kept my starter going for five years. I take the silicone ring off the bamboo lid when I want a rigid cover with a little airflow, so pressure doesn't build up. It's a handy option alongside the cloth.
I use this straight-sided jar for starter and discard. The included black spatula gets around the smooth bottom curve without leaving starter stuck in corners or shoulders. Cleanup is quick, and honestly it looks pretty sitting on the counter too.
My wife broke her old starter jar, which was not a good day, so I got her this one. She loves it. The black bands help track the rise and give you some grip, and the 100–900ml markings are easy to read.
My textured Ball jar was making me lose my mind trying to wipe the sides down and prevent mold. This one is smooth and straight with no shoulders, and the slim black spatula gets the leftover starter off the walls easily.
I'm new to sourdough and really appreciate the clear black markings from 100ml to 900ml. I move the rubber band to the starter level after feeding, and between that and the markings I can easily see when it doubles.
I've kept bigger starters and smaller ones, but this setup feels just right for me. I usually maintain mine around 200–300ml, so there's lots of headroom in the 900ml jar when it gets active.
This wide-mouth straight jar setup is legit. You get the stick-on Celsius and Fahrenheit thermometer, extra linen covers, chalkboard labels, and a white marker all in one box. Simple and useful.
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Yes. The Cosari LevainPro features an 8.5cm (3.35-inch) collarless straight opening with zero inward neck lip, allowing an adult hand and sponge to reach right down to the bottom corners effortlessly.
During active countertop fermentation, use one of the 3 breathable woven linen cloth bonnets to allow aerobic gas exchange while blocking dust and pests. When storing your starter or discard in the refrigerator, switch to the natural bamboo lid with its food-grade silicone gasket for an airtight seal. You can even pop the removable silicone ring out of the bamboo lid if you want a rigid wooden dust cover on the counter that still lets a whisper of air through.
It is engineered to handle both. Because the printed graduations begin right down at 100ml, a small 40g–50g daily maintenance starter sits clearly visible near the base. When you build a larger 300g–400g levain for a weekend bake, the 900ml ceiling gives your starter plenty of headroom to double or triple without overflowing.
Yes. Unlike competing kits that show black labels in their product photos but forget to include a pen, the Cosari LevainPro kit includes 6 reusable chalkboard labels and 1 white chalk marker pen right in the box.
The peel-and-stick liquid-crystal thermometer adheres vertically to the lower exterior of the glass and reads from 16°C to 34°C (61°F to 93°F) in 2°C increments. The active temperature highlights automatically—making it easy to keep your starter in the ideal 24°C–28°C (75°F–82°F) fermentation sweet spot.
Active sourdough baking gets messy with flour and wet dough. Including 3 breathable linen bonnets and 3 matte-black rubber tracking bands ensures you always have a fresh, clean cover and band ready while another is drying after a wash—or lets you outfit a second discard jar.