Fermentation Weights: Why Your Vegetables Float, and What It Actually Costs You

Why do fermenting vegetables float? Because fermentation makes gas, and gas floats.

That's it. That's the answer. Your veggies are bobbing up there because the ferment is working! The good bacteria are chowing down on the sugars in that cabbage and burping out carbon dioxide, and those little bubbles get trapped in every fold and crevice. A shred of cabbage full of gas is basically wearing a tiny life jacket. So up it pops.

Nothing's wrong. Here's the catch, though: anything that pokes up above the brine is now sitting in open air, and air is where the trouble starts. Floating costs you in three flavors, from mildly annoying to genuinely expensive. And the sneakiest one? The USDA spells it right out, and almost nobody reads that far.

Why they float in the first place: blame the bubbles

Lacto-fermentation is supposed to make gas. That's the whole gig. The bacteria you WANT turn sugar into lactic acid (that's your tang) and carbon dioxide (that's your fizz). Right around days three through seven, your jar starts looking like a lava lamp and acting like it's up to no good. It isn't. Those bubbles are the receipt!

Quick tip while we're here: if you're a week in and there's no bubbling and no floating and no drama at all... floating isn't your problem. Temperature is. The USDA is refreshingly blunt about sauerkraut on this one. At 70 to 75 degrees, you're fully fermented in about 3 to 4 weeks. Drop to 60 to 65 and it's more like 5 to 6 weeks. Below 60? It might just sit there and sulk and never ferment. Above 75 and it can go mushy on you. So that cold basement isn't a safer ferment. It's just a slower one.

What floating actually costs you: a flavor tax, a dead batch, or your whole Saturday

Folks treat "keep it under the brine" like some vague thing Grandma used to say. Nope. It's specific, and here's the bill, cheapest to priciest:

Now, stay kahm about that first row! White film on a ferment sends people into a full panic every single August, and nine times out of ten it's the harmless stuff. The tell is texture: kahm yeast lies flat like a skin, mold stands up and gets fuzzy. Truly can't tell? Play it safe and start over. A head of cabbage isn't worth the gamble.

The USDA quietly admits your WEIGHT decides how much babysitting you signed up for

Here's the line nobody quotes, buried right in the middle of the USDA's own sauerkraut instructions:

"If you weigh the cabbage down with a brine-filled bag, do not disturb the crock until normal fermentation is completed (when bubbling ceases). If you use jars as weight, you will have to check the kraut 2 to 3 times each week and remove scum if it forms."

Read it twice. Same cabbage. Same salt. Same three to four weeks. Two totally different chores for the poor soul who has to live with the jar. Do the math: three to four weeks at two or three check-ins a week is 6 to 12 separate trips to that jar, spoon in hand, skimming gunk off the top each time. Or, option B: do not disturb. Zero trips. Zip!

So what makes the difference? Whether the top of your ferment stays covered. A brine-filled bag flops down and blankets the whole surface, so scum's got nowhere to move in. Stack a couple of little jars on top as makeshift weights and you leave gaps around the edges, which is exactly where the film moves in. Keep the surface covered and you barely babysit it. Leave it open and you're skimming all month. Good news: you can get that fully covered setup in a plain mason jar, and it's stupidly simple!

What a pickle pebble actually is (and the one cabbage-leaf trick that makes it shine)

That channel across the middle? Finger grip. It's the difference between plucking the weight out in a second and going fishing in cold brine up to your knuckle.

A Pickle Pebble by Masontops ($21.99 regular mouth, $23.99 wide mouth) is a chunky domed puck of soda lime glass, the very same glass your jar's made of. It drops straight into the jar and sits right on top of your veggies, holding everything down under the brine. Think of it like setting a smaller jar on top to weigh things down... except it actually FITS, because Masontops sizes it to the mouth: the wide-mouth pebble is 2.75 inches across and 0.75 inches thick, against jar mouths of 2.75 inches regular and 3.38 inches wide. A random little jar from the cupboard is a guess. This is a fit!

Now, the pebble's a hair narrower than the opening, and it has to be. Seal that mouth airtight and the carbon dioxide's got nowhere to go, and congratulations, you've built a tiny glass bomb instead of a jar of pickles. So there's always a little gap at the rim, and a stray shred can bob up through it.

Here's the fix, and it's the best kraut trick we've got: before the pebble goes in, take one whole outer cabbage leaf and lay it flat over the shreds, then set the pebble on top of the leaf. Now the pebble isn't wrangling a hundred loose bits. It's pressing on one solid lid of cabbage that spans the whole surface, so everything underneath stays put and completely under the brine, even though the pebble never reaches the edges. One leaf. That's the whole secret!

Couple things the photos show that no spec sheet bothers to mention. First, that molded finger channel, which is a genuinely clever little bit of design, and sounds like nothing right up until you've tried to fish a plain flat disc out of a jar of brined cabbage. (Ask us how we know.) Second, oh yay, it's clear glass on purpose, so you get a front-row seat to the whole show instead of squinting at an opaque hockey puck!

One honest word on the box, though. The Pickle Pebbles packaging runs a little "versus other fermentation weights" chart, all percentages, 100 here and 60 there at keeping veggies in brine. We have zero idea where those numbers came from, so we're not about to parrot them like somebody actually tested them. The design difference in the photo is real, and you can judge it with your own two eyes: a domed puck with a grip channel, or a flat disc with nothing to hold onto. That comparison's fair game. The bar chart's just decoration.

Weight and airlock: it's a sweater AND a coat

Four jars, four ferments, four colors of silicone. The color-coding isn't for looks. It's how you remember which jar's the garlicky one.

Here's where the internet muddles things, so let's untangle it. A weight and an airlock aren't rivals, and you're not picking a winner. They're a sweater and a coat: each has its own job, and you're a whole lot cozier wearing both. The weight keeps your food down under the brine. The airlock handles the air.

Pickle Pipes by Masontops ($21.99 regular mouth, $23.99 wide mouth) are the airlock half. They're one-way silicone valves that tuck under a regular screw band. Gas out, oxygen stays out, and you never have to burp a jar again! They're only half an inch thick, so a whole shelf of them still lets the cupboard door shut.

Now, here's where we gently part ways with the box. The Pickle Pipe packaging says the pipes are "specially designed to prevent mold." We'd say it a touch differently, because we'd rather level with you than sell you. An airlock keeps fresh air out, which absolutely helps. But the thing that actually stops mold is keeping your food down under the brine, and that's the weight's job (plus that cabbage leaf). The pipe's a great teammate. It's just not the whole team. Sweater AND coat.

The mouth-size trap, which costs folks more money than anything else on this page

Masontops actually prints the numbers, which we love them for. Just note: these are the WIDE MOUTH kit dimensions. The regular-mouth pebble runs smaller.

Everything in this aisle comes in two sizes, and a wide-mouth weight in a regular-mouth jar is just a fancy coaster. So don't get burned:

• Measure the mouth, not the jar. Brand, height, volume? None of it matters. Masontops measures edge to edge across the rim: 2.75 in / 7 cm regular, 3.38 in / 8.6 cm wide. A tape measure beats a guess every time!
• Pickle Pebbles come in both, four to a set. Weird little quirk worth knowing: the wide-mouth box is branded "Pickle Pebbles PLUS+" and the regular-mouth box is just plain "Pickle Pebbles." Same idea, two bucks apart.
• The Complete Fermentation Kit ($54.99) is WIDE MOUTH ONLY. Nine pieces: 4 pebbles, 4 pipes, the acacia packer, and a color recipe book. Buy the pebbles and pipes on their own and you're already within a few bucks of $46, so the packer and the book are basically along for the ride free!
• Heads up, our Superb jars are regular mouth, and we'd rather flag that here than have you find out at the counter. Grabbing Regular Mouth Pint Mason Jars by Superb ($24.97 for 12)? Then you want the regular-mouth pebbles, not the kit.
• The packer's the one thing that fits both. The Acacia Wood Pickle Packer ($17.99) is 10 inches long and tapers from 2.5 inches down to 2, so it drops into either mouth. It also moonlights as a cocktail muddler, which is a mighty fine second career for a cabbage stomper!

Do you even need to buy one? Here's the honest sorting hat

Pebble goes on top of the food, under the liquid. That's the whole operation. Truly.

• Fermenting once, just to see if it's your thing? Improvise! A whole outer cabbage leaf folded over the shreds with a little jelly jar of water on top does the trick for free.
• Fermenting more than twice a year? Buy the weights. Four pebbles at $21.99 shakes out to about five and a half bucks a jar, once, forever. Stack that against 6 to 12 skimming sessions a batch and it stops being a close call real quick.
• Got weights already and STILL fighting the film? You need coverage, not more heft. Cabbage leaf UNDER the pebble, every single time.

Too late, it's already floating. Now what?

First rule: don't dump it! Here's your play-by-play:

• Push it back under with a clean utensil and drop a weight on top. Catching this on day four is a full fix, not a rescue mission!
• Top off the brine if it's running low. The USDA's top-up for kraut is 1.5 tablespoons of salt per quart of water, boiled and then cooled. Never plain water, which waters down your salt and rolls out the welcome mat for all the wrong microbes.
• Skim any film with a clean spoon (stainless steel is totally fine here, no need to hunt for a special one). If it's kahm yeast, skim it and then move the jar to the fridge, because it'll just keep coming back at room temperature no matter how carefully you work.
• Fuzzy mold? That one's done, friend. Wash everything in hot soapy water, rinse hot, and start fresh with the weight in from day one.

And one thing that catches people off guard: a finished ferment doesn't have to live in the fridge forever. The USDA says fully fermented kraut keeps in the refrigerator for several months, or you can can it in a boiling water canner. Ferment first, can second. The two hobbies get along great!

FAQ: the fermentation questions we field at the counter every week

Why do my vegetables float even when I use a fermentation weight?

Usually because a piece slipped out around the edge before the weight went on, or the brine dropped below the weight. A glass weight is narrower than the jar on purpose so gas can vent past it, and small shreds can drift right up through that same gap. The fix is a whole cabbage leaf laid over the food underneath the weight, which turns a little disc into something much closer to full coverage.

Is the white film on my ferment kahm yeast or mold?

Look at whether it stands up. Kahm yeast is a flat, thin, wrinkly white skin lying on the surface, and it's harmless, though it'll dull the flavor. Mold is fuzzy and raised, in blue, green, black, or white. The National Center for Home Food Preservation says not to taste a ferment if you see mold, feel a slimy texture, or smell a bad odor. When you can't tell, start over.

What size fermentation weight do I need for a mason jar?

Match the mouth, not the jar volume. Masontops measures a regular mouth at 2.75 inches and a wide mouth at 3.38 inches across the rim, and builds Pickle Pebbles in both. A quart and a pint of the same mouth size take the same weight, so measure the opening and ignore everything else.

More from our pickling and fermentation series

• How to Make Sauerkraut in a Mason Jar (No Crock, No Grandma Required) - the full step-by-step, where these weights do their day job.
• Pickling vs Fermenting: 3 Ways to Make Pickles, and Only One Needs a Canner - not sure which method you're even doing? Start here.
• How to Keep Pickles Crunchy: 7 Methods, Ranked by What Actually Works - floating is one of the four things that softens a pickle. Here are the other three.
• Regular Mouth vs Wide Mouth Mason Jars: There's No Wrong Answer - since your weight has to match your jar, here's how to pick the jar.

Everything you need to keep those veggies under the brine

Shop pickling and fermentation gear →
Glass weights, airlock lids, packers, kits, and jars, in both mouth sizes. Current availability is right there on each product page.

Related reading: Pressure Canner vs Water Bath: One Rule Decides What You Can Safely Can →
Once your kraut's fully fermented, you can put it up on the shelf. This one sorts out which canner the job calls for, and why it all comes down to a single number.

Got a jar doing something weird on your counter right this minute? Email us at support@kooihousewares.com and tell us what you're looking at. Anna and the crew up in Muskegon have seen a whole lot of ferments go right and a few go sideways, and a good description of the film is usually all we need to call it.