Emma Christensen wrote the book on home brewing, True Brews, which is why we've turned to her for help on what to do if your batch of kombucha isn't working out the way you'd planned. [It kind of goes without saying that if you are reading this, you know a thing or two about kombucha, but if not, here's Food Republic's 8 Things You Didn't Know About Kombucha.] Here's Emma's helpful guide to Troubleshooting Kombucha, and there's even more advice in True Brews, which is a great place to start if you want to make your own batches of this delicious fizzy drink.

See also: Emma Christensen Knows Everything About Home Brewing

Reprinted with permission from True Brews by Emma Christensen, copyright © 2013. Published by Ten Speed Press, a division of Random House, Inc.

My scoby has developed a hole. Is it still okay to use?
Physical imperfections in the scoby, like holes or tears, are really nothing to worry about and are usually just an aspect of the scoby reacting to its environment. Holes are sometimes caused when escaping carbon dioxide pushes its way through the scoby; clear jelly layers form if the jar of kombucha was jostled at some point during fermentation and a new layer of scoby starts to form; dried patches sometimes happen in the winter when the air lacks moisture; dark patches sometimes develop where the yeast gets stuck inside a layer of scoby. You might also notice changes in your scoby as your house gets warmer or colder with the seasons, or if you move a scoby to a new house or apartment — this is just the scoby getting used to changes in the environment.

There's a weird odor coming from my fermenting kombucha. How do I tell if it's good or bad?
Since most of us haven't been around fermenting foods and beverages, it can be a little tricky to know what's normal when making kombucha and what might be a warning sign that something not-okay is going on. In general, if you follow the recipe and maintain a consistent ratio of water, sugar, tea and starter tea (i.e., prepared kombucha), then your kombucha will ferment just fine — the only times problems start to arise is if you forget to add one of the ingredients or suddenly use a different proportion of one of them. Scobys really like consistency.

A healthy scoby fermenting a batch of kombucha will have a sour, vinegary aroma (think: buttermilk), which will gradually become stronger the longer it brews. If you taste the kombucha every few days, you should notice it gradually starting to taste more tangy and sour. Once you make a few batches, you'll start to understand the normal range of aromas and flavors in your kombucha while it's fermenting, and then you'll know right away when something isn't quite right. If you're ever in doubt about whether your kombucha is ok or not, continue brewing batches as normal, but throw away the kombucha that you make — if something is truly wrong, it will become worse and worse to the point where it's obvious and there's no question.

I think there's mold growing in my kombucha. How can I tell if it's mold?
Honestly, I've never had mold grow on my kombucha, so I can't definitively tell you! From talking to other people and doing my own research, if your scoby starts growing mold, it will look like something that's been left in the fridge for too long. It will look fuzzy and black and very, very different from the scoby itself. But again, as long as you maintain your ratio of ingredients and keep the scoby covered while it's fermenting, you shouldn't have a problem. The only times when you get mold is if you use a tea that contains essential oils (like Earl Grey or some chai teas — just check the ingredients list on the tea), if you continuously use decaf tea over several batches, or if you use too much sugar. I haven't heard of mold growing as a result of any conditions other than those.

I know it's good to peel the oldest layers away from your scoby occasionally. How can I tell which is the oldest layer if it's flipped on me?
Scobys darken as they age so you can always tell which is the oldest layer by which is the darkest layer. If it's too close to tell, then it probably doesn't matter! Scobys will last a very long time, even if you use the same layer again and again — it's only when they start to get really dark-dark brown that they stop working very well. My recommendation is just to discard the oldest layer every few batches. As far as I know, a scoby will last indefinitely that way.

What should I do if my kombucha isn't carbonating after a couple of days?
Sometimes kombucha seems like it takes forever to carbonate, especially if it's cold in your kitchen or if you're bottling the kombucha straight from the jar (meaning, most of the sugar was consumed during fermentation so not much is left for the yeast to eat while you're carbonating it in the bottle). You can kickstart the yeast and make fizzier kombucha by adding some form of sugar — either a spoonful of table sugar, a spoonful of honey, or some fruit. Also, make sure your kombucha is somewhere warm — above 70 degrees is ideal.

I'm not sure if the lids on my jar are tight enough. How airtight do they need to be?
To get really fizzy kombucha, the jars need to be airtight. Swingtop bottles create a really good seal — just watch for signs that the rubber is drying out or cracking over time. If you're re-using bottles from store-bought kombucha or using recycled plastic soda bottles, just know that the seals on the caps will wear out after a while. If you notice that your kombucha is becoming gradually less fizzy, try replacing your bottles. (P.S. If I bottle a batch of kombucha in glass jars, I like to still fill one small plastic soda bottle. This is my indicator for when the kombucha is fully carbonated — when that plastic soda bottle is rock solid to the touch with very little give, I know the whole batch is carbonated.)

I can't seem to get the balance right between sweetness and tartness. Any tips?
If your kombucha is fermenting normally, it will definitely become more sour as time goes by — you don't have to worry about that! The time it takes to make a batch of kombucha is affected by temperature — cold temperatures make the scoby slow down, so brewing will take longer in the winter (conversely, you can make batches much more quickly in the summer when your kitchen is warmer!). The more you brew, the more you'll understand the cycles of your scoby and how long batches take. If your kombucha still tastes like sweet tea after a week, then something has likely gone wrong with your scoby and you should start completely over with a new scoby.