Troubleshooting Guide
Outsmarting Mold, Funk, and Other Fermentation Foes
So you’ve read all our Brew Wild guides, Amazon Primed your entire brewing setup, brewed your first batch… and now something feels off. Is it supposed to smell like that? Should your brew jar look like a sepia jellyfish lava lamp? Did you accidentally summon a vinegar demon? Don’t panic. We’ve exorcised worse.
Let’s start with one thing: You followed our brewing instructions, right? No shortcuts. No rinsing your jar with a garden hose. Because troubleshooting only works if you’ve minimized the chaos. You’re a booch scientist now—controlled variables are the name of the game.
If you skipped Kombucha 101, BEFORE you Brew, and our other guides, go back and read them first. We’ll wait (and you’ll be entertained, promise).
Still here? Great. That means you did everything mostly right… and something still feels off. Lucky for you, we’re professional brewers—and we’ve made every mistake in the book. Chances are, whatever mystery is bubbling in your jar, we’ve seen it. And we’ve got answers.
Mold: The Evil Overlord of Bad Batches
If you’ve brewed kombucha before, you know the fundamental question:
Is it mold… or just ugly?
Mold is the ultimate kombucha villain—lurking in the air like a curse, silent and patient, waiting to strike. One day, your SCOBY is a loyal companion, bubbling with potential. The next? A traitor cloaked in fuzz.
There’s no saving it.
No redemption.
No farewell ceremony elaborate enough to honor the friendship you once shared.
All that’s left is to dump the jar, whisper a tearful goodbye, and begin again—wiser, stronger, but with a piece of you gone.
Tragic? Yes.
Preventable? Also yes.
Here’s how to spot mold and keep your SCOBY from succumbing to the darkness.
How to spot mold
It’s fuzzy. It’s blue, green, black, or white. It can grow on the liquid or on the pellicle.
Even if it’s only appears on the surface, it’s everywhere. Don’t even think about reusing the liquid.
How to Prevent Mold (A.k.a. Basic SCOBY Safety)
• Sanitize everything. If it touches your booch, hit it with straight vinegar. No soap, no mystery cleaners—just the cheap stuff that smells like Easter eggs.
• One‑day helmet. For the first 24 hours, cap the jar with a lid or plate on top of your cloth cover. It’s a temporary force‑field against airborne gremlins while your culture establishes its new territory. As long as there's enough headspace, the culture will get all the oxygen it needs. Day 2? Pop the lid off, but keep the cloth.
• Audit the real estate. A pitch‑black closet sounds perfect—until you remember stale air is mold’s love language. Pick a spot that’s out of direct sunlight and gets a air flow (kitchen counter, book‑shelf, top of the fridge).
• Hold the temp line (70‑85 °F). A lively SCOBY out‑competes mold. Dramatic temperature swings—daytime sauna, nighttime tundra—invite disaster.
• Yes, the Heat Mat. We know, we sound like shills for BIG Heat Mat™. But twelve bucks buys peace of mind and eternal kombucha glory.
Kahm Yeast: The Wannabe Supervillain of Brewing
Kombucha is meant to be funky—but even funk has its limits.
Kahm yeast won’t hurt you or your brew, but it will make your kombucha taste… off. Think of it as the henchman of a supervillain—not evil enough to destroy the world, just annoying enough to derail your plans.
It’s not dangerous on its own, but it signals a deeper problem: an imbalance in your culture. Kahm yeast can raise the pH of your kombucha, making it more vulnerable to mold and other infections. So no, it’s not mold-level serious—but it’s not something you want to ignore either.
The good news? Your SCOBY can recover. Here’s how to spot it, and what to do next:
How to Spot Kahm Yeast
It’s trickier than mold, but kahm yeast usually appears in one of two forms:
A thin, matte film with a tight, rippling texture (like a brain with no thoughts). Or, stringy shriveled strands. Kahm yeast can cover the entire pellicle, or just a portion
Flavor-wise? It might taste totally normal—or it might go full farmhouse funk. If it’s giving “barnyard saison,” it’s probably time to dump it.
How to redeem your culture and save the realm.
Don't panic. Kahm yeast isn’t harmful on its own. If your kombucha smells fine, tastes normal, and isn’t sprouting mold or turning weird colors, you’re still in the clear. No need to yeet the jar—yet.
Remove the yeast. If the pellicle looks like it’s being overtaken by the undead—with a wrinkly brain texture or stringy, web-like tendrils—it’s time to chuck it and say a quick prayer. If you act fast and adjust the environment, a fresh (non-zombie) pellicle can grow back.
Boost oxygen. Kahm yeast loves a stagnant vibe—don’t give it one. Make sure your jar has enough headspace and that your cloth cover allows for proper airflow. If things are looking a little too cramped, pour out a bit of liquid when you remove the pellicle.
Weak Starter. A sluggish SCOBY leaves the gates wide open. This vulnerability shows up in two ways:
• Low numbers. If your starter doesn’t have enough yeast and bacteria, it takes too long to build defenses—giving invaders like Kahm yeast time to swoop in and ransack the sugar stores. Remedy: use more starter in your next batch until the numbers rebound.
• Low activity. Sometimes the troops are there… they’re just lazy and disorganized. If your bacteria aren’t active enough, they’ll get overrun by Kahm before the real fermenting begins. Solution: use more starter next batch—or consider recruiting a new, battle-ready culture. How to grow your own culture here
And finally… temperature regulation.
…Don’t make us say the H-word again.
Yes, the Heat Mat. We know, we know: BIG Heat Mat™ propaganda. But hear us out: When temps drop, your bacteria slow to a crawl—while yeast? Oh, they keep going… plotting. The result? A microbial coup, with Genghis Kahm leading the charge.
The opposite can also be true—too-high temps can trigger a Kahm invasion. Not impossible, just less common in our experience. If you’re fermenting HOT (like, above 90°F) and Kahm creeps in, that could be your culprit.
Keep your brew warm and steady (70–85°F)—minimize temp swings. No sudden chills, no heat spikes. Just a nice, stable climate to keep the bacteria on watch to prevent a full-blown yeast uprising. Order is maintained. The realm is safe.
And this actually segues into the next topic perfectly.....
Alcohol: Our 12-Step (Okay, Like 3-Step) Recovery Plan
Remember back in the Kombucha 101 when we talked about the dynamic duo: yeast and bacteria? Yeast makes alcohol. Bacteria turns that alcohol into vinegar. Maintaining harmony between these two chaotic roommates is the key to a healthy culture.
But if the bacteria takes a vacation and the yeast throws a house party? They crank out alcohol like it’s spring break in Daytona—and with no bacteria around to clean up the mess… well, congrats. You’ve accidentally brewed hard kombucha.
Or maybe… deep down… that’s what you wanted all along.
The Kombucha Hangover: Getting Back on Track
So—your booch is buzzed. Why?
Too low of a temperature. Blah blah blah 70–85°F (You remember the yeast coup from moments ago?) We’re not even going to tell you how to fix this. If you can’t guess by now… what have we even accomplished together?
If you finally did something right and got a heat mat, the other suspects:
Not Enough Oxygen.
Yeast are anaerobic little goblins—they thrive in low oxygen and crank out alcohol like it’s the day before prohibition. Without enough airflow, your bacteria can’t keep up, and things get boozy fast.
More oxygen. Leave more headspace, use a wide-mouth jar, maybe even get it a fan (kidding—but maybe?). When transferring your sweet tea, let it splash as you pour (just don’t drown the pellicle). That splash helps introduce oxygen, giving your bacteria a fighting chance.
Too much sugar. A minor character, but still shady. Excess sugar gives yeast the upper hand and tips the culture out of balance.
Fix it: Reduce sugar by 10–20g per batch—or better yet, stick to the ratios in our Brew Guides. No need to yank the rug out from under your microbes.
Too yeasty of a starter. If your starter looks more like swamp juice than kombucha, it’s overloaded with yeast. More yeast = more alcohol.
Solution: Strain the excess, show it the door, and reset. (Our Continuous Brewing Guide has all the SCOBY glow-up tips.)
...are we starting to see a theme emerge? Good. Because your microbes sure have. Warmth, airflow, sugar balance. The sacred trifecta.
Tiny Terrors of the Tea Realm
Not world-ending. Just annoying enough to make you question everything.
Now that we’ve vanquished the big baddies (mold, Kahm yeast, accidental hard kombucha), it’s time to face a few lesser foes.
Legs? Optional. Protecting the brew? Mandatory.
Acidity
The bacteria in kombucha thrive in a low pH—it’s their happy place. So what do they do? They build themselves a vinegar jacuzzi and soak in it like they’ve booked a weekend spa retreat. The longer they lounge, the more sour your brew becomes.
Everyone’s got their own acidity sweet spot. Some like a delicate tang. Others want a slap in the face. We give you a baseline of 150g sugar per gallon, but every culture ferments a little differently—so plan to adjust as you go.
So Sour It Bites Back? Here’s the Fix.
• Decrease your fermentation time. Sourness builds the longer the bacteria are active. Try taste-testing your brew 3, 2, and 1 day before your usual finish line to find your ideal point.
• Reduce your sugar slightly. If it still tastes too sour even when the sweetness is right, try cutting back the sugar in your next batch by 10–20g. Paired with a shorter ferment, this can bring balance without losing your preferred sweetness.
• Mind your starter volume. Too much starter can launch your brew into Sourville with no return ticket. Stick with 12–16oz per gallon to keep things in check.
Needs More Bite? We Got You.
Vinegar is a good thing. It means your culture is healthy and working. If there’s no acidity at all, that could be a red flag—your SCOBY might be weak, inactive, or just plain tired. In that case, it’s probably time to start fresh (you can learn how to grow a SCOBY from scratch with our Batch Brewing Guide.
But if you’re getting some tang and just want more—here’s how to turn up the sour:
• Ferment longer.
Beginners tend to cut fermentation short—especially when you’re unsure what “done” tastes like. Give it a few extra days. Let the culture do its thing.
• Increase the sugar.
If your booch is barely sour and not very sweet, there’s a chance you’re making hard booch (see above) or underfeeding your bacteria. More sugar = more fuel for vinegar production. Try bumping your sugar by 10–20g in your next batch.
• Check your starter volume.
Too little starter = weak launch. Your acidity won’t develop properly, and you might get some weird off-flavors (ask us how we know). Stick to 12–16 oz per gallon for best results.
Water: Friend or Foe?
If you’ve found yourself between a rock and a hard place—brew after brew falling flat despite your noble efforts—it might be time to look inward (like, into your plumbing) and ask:
Is my water foiling all my plans?
Despite popular belief, minerals in water can actually help your SCOBY—depending on what kind they are. In fact, many commercial brewerys add minerals back into the water to support a thriving culture.
So no, tap water isn’t necessarily the enemy. But water that tastes like a swimming pool? That’s a red flag. Chlorine and chloramines can mess with your culture’s chi. If your tap water smells or tastes like a public pool, filter that bad boy first.
That said, don’t overthink it—sometimes the only way to know is to test it.
If you’re doing everything else right, but your brew still isn’t behaving, and you’re using tap water? Try switching it up:
→ Using filtered water? Test a batch with tap.
→ Using tap? Try filtered or spring water instead.
If you’re a committed booch scientist, try running two fermentations at once with different water sources and compare the results. You might be surprised by what your culture prefers.
Sometimes, the key to unlocking your best booch is a little water wizardry.
How to Woo the Flavor Maiden (Without Scaring Her Off)
If you’re following our Batch Brewing or Continuous Brewing guides—nailing the temperature, tea amount, and steep time—your kombucha should be well-balanced (like a juggler on stilts). But hey, if you’re craving a different result? Who are we to stop you.
This might seem obvious, but we’re going to say it anyway:
More tea = more flavor. Less tea = less flavor.
If you’re hoping to tweak the strength of your brew—or the fruitiness (if you’re using Brew Wild blends)—do it gradually. Sudden environmental shifts can send your culture into a mild identity crisis.
Start by adding or subtracting just 5g of tea per batch.
Small steps = smooth transitions = happy SCOBY.
Time for Some Tough Love
This guide is here to help you fine-tune your brew—making small, deliberate tweaks to bring your culture in line with your taste. But if your kombucha is waving multiple red flags—no vinegar, weird flavors, syrupy sweetness, general chaos—it might not be you.
It might just be a bad culture.
At a certain point, it’s easier to start fresh. Don’t drive yourself crazy trying to fix your SCOBY like your tattooed ex-boyfriend (Sorry—he’s not changing for you.) Dump it. Set yourself free. Reclaim your peace.
Need a fresh start? For a step-by-step guide to starting over the right way, check out our Batch Brewing Guide (and honestly, the other ones too—because your last SCOBY definitely didn’t give you the full story).
Grow your own SCOBY:
Don't forget the check out the rest of our 📜 sacred brew texts: