In today's special post, my wicked smart sister Carolyn explains the ins, the outs, the whats and the whys of homemade kombucha! You can trust her because she's literally a Doctor in this stuff. (She holds a Ph.D. in Chemistry. She currently works at Americas Test Kitchen. It's not relevant but she's also a natural talent for all things musical and likes unconventional house pets. You can read more of her thoughts on her excellent blog, Chemical Intuition!).

Unlike the Whole Foods versions, Carolyn's home-fermented teas are strong, un-pasteurized, and extremely affordable. She is currently experimenting (in, like, a legitimate way – i.e. not the way I experiment with eyeliner) with all sorts of very pretty flavorings, like turmeric + honey, lavender, and even dragonfruit. 

Read on for her method, her madness, and how to bring up a baby SCOBY!

(And as a PSA, my mom has helpfully provided some links warning you, me, and everyone we know of the dangers of homemade kombucha. You've been warned here and here.)

I first got excited about fermentation in the first few years of graduate school. There, I met my friend Kyle, who is a total beer guru. He can remember a beer he drank several years ago and knows how to brew beer, really, really well. I learned some things about brewing from Kyle, and he and our friends got together to brew several beers, calling our brewery Monks in Space.

I ended up getting obsessed with kombucha, though I felt that the grocery store varieties were timid and overly sweet. But then I found some of Sandor Katz's stuff. He is a fermentation expert (a "fermentation revivalist") and has written several books on the subject, with recipes and folklore and his own anecdotes. He emphasizes that anyone can ferment, that people have been doing it for thousands of years, and that it isn't just the domain of the experts and specializers. 

I now brew my own kombucha on a fairly decent scale. At any time I can brew up to 6 L of kombucha using two different large SCOBYs (see below), each in its own, food-safe glass jar. Here I will tell you a detailed recipe for growing your own SCOBY, brewing the right type of tea, fermenting your kombucha, and finally, bottling your kombucha so you end with a delicious, unique, and bubbly beverage.

First, get your hands on the following supplies. This list is for fermenting 2 L of kombucha. Check your local Goodwill and look at brewing supply stores for these things (and also just go ahead and use Amazon if all else fails). 

  • One 4 L capacity food safe glass jar with a wide mouth lid. The microbes need oxygen to grow, and the wider your mouth, the better. A punch bowl will be too wide; you need something that you can drape a paper towel over to cover and keep tight with a rubber band or tape. 
  • pH strips: you want the scale to go down to 0 and go up to at least 8. I recommend strips that go from 0-14. 
  • at least 8 Grolsch bottles, or other thick, able to withstand pressure, glass bottles with a swing top. 
  • a bottle of plain commercial kombucha from the store, unopened (i.e. don't drink from this! you will use this to grow your own SCOBY).
  • 4 black English tea bags. Plain black tea of any kind is great. You can also use green tea. I'd recommend starting with standard issue English black tea.
  • 1/2 cup of sugar (granulated, white)
  • plenty of paper towels or 1 thin dish towel
  • a large rubber band that can fit snugly around the top of your glass jar 
  • 4 x 1 L glass jars, like a Mason jar
  • Optional: Flavorings of your choice for a secondary fermentation: 1-2 tbs dried fruit, edible flowers, anise seed, ginger, etc. 

Editor's note: it took me a minute, but that means you need one giant (4L) jar with a lid, four Mason jars or similar 1L glass jars, and at least 8 Grolsch (or similar) bottles. Bottles galore, in other words.

A note on sanitation and contamination concerns:

You may be worried that if you grow your own microbe community at home and try and ferment your own drinks, you might just end up killing yourself. If you go in with carefulness and good information, you'll have nothing to worry about! The key to success with kombucha are the following: 

Here's a SCOBY in the making (on its way, but here is just some yeast floating around).

Here's a SCOBY in the making (on its way, but here is just some yeast floating around).

  • In all steps, make sure that your hands are freshly washed with soap and hot water, and that all of the stuff you're using (jars, spoons, bottles) are also freshly washed with hot, soapy water and well rinsed. 
  • Also, be sure to check the pH of your brew as you go. This part is important!
  • Once your SCOBY is fermenting, be on the lookout for contamination. Contamination will look like fuzzy growth or anything that looks like it has mycelium (like a fungus). The SCOBY of course can look fairly strange...a slick, woggly look is to be expected. Strands of yeast culture floating in the tea, separate from the SCOBY mass itself, are also normal. For more information on how to prevent contamination and to check out photos of what's good, what's bad, and what's just perfectly normal SCOBY looking a little yeasty,  read this from Brooklyn Kombucha.

Step 1: Grow your SCOBY, or buy it.

If you want to grow your own SCOBY, pour the commercial kombucha into one of the Mason jars. Stir with a clean chopstick or spoon, mixing to make bubbles and incorporate a ton of air. Cover with a paper towel and put the rubber band around the lid. Let this sit at room temperature in a not hot or cold area (I put mine on top of my fridge) and let ferment with the paper towel covering for about a week, or until a thick layer of SCOBY grows. At this point, check the pH. It should be around 2.5 to 3. If it's higher, keep incubating for a few more days. 

Hey, whats a SCOBY? a SCOBY is a Symbiotic Community of Bacteria and Yeast that converts sugary solution to an acidic, bubbly one. The yeast eat the sugar (sucrose) and convert it into ethanol and carbon dioxide (CO2). This is like what yeast do in beer fermentation. But unlike in beer, in kombucha making there's a second type of metabolism happening, too! The bacteria in the SCOBY take the ethanol made by the yeast and convert it to acetic acid. The bacteria need oxygen to convert the ethanol to acetic acid. Think about what happens when you leave your red wine on the kitchen counter after it's been opened. After a few days, it will start to get acidic. It's the same type of bacteria that make your wine turn to vinegar that ferment your kombucha.

If you can't find a commercial SCOBY, you can always order one online. There are many resources out there, like this one: Brooklyn Kombucha.

Step 2: Brew your tea.

The next step is to brew your own tea. You have two options with the water that you choose. You can either use spring or your own city's tap water. I've had luck with both. Since we are boiling the water, any issues with contamination or chlorine that may be in your tap water are dealt with by boiling. If you're worried, just go ahead a buy a gallon of spring water from your local corner store.

In a large, clean pot add 2 L of water, the 1/2 cup of sugar and heat to bring to a vigorous boil. Turn the heat off, and add the tea bags, cover, and let incubate for 15 minutes. Remove the tea bags, and cover. Let cool to room temperature. I usually brew my tea at night and do the next step the next morning. 

Step 3: Combine SCOBY and tea in the large glass jar. 

Now that you have a healthy baby SCOBY from the first step, we'll go forward! Place the SCOBY in the large, 4 L capacity glass jar. Transfer along with the SCOBY any of the liquid that was with it in its previous container. If you grew your own SCOBY, this will be the tea from the commercial kombucha you used to grow it. The pH should be around 2.5. Add the 2 L of room temperature sugary tea you brewed in the last step. Check the pH. It should be around 3.5-4.0. If it's higher, add more plain commercial kombucha until the pH registers 3.5-4.0. Cover the glass jar with a single layer of paper towel or a thin dish towel and secure the top using a rubber band. 

Step 4: Ferment! 

Let your tea ferment in for about one week. Check the pH and taste every day. The pH should steadily decrease until it reaches 2.5. Usually at this point, the tea is ready to bottle. You may prefer a sweeter or tarter tea. Taste and follow your taste buds! Once it's reached the level of sweetness/tartness you like, proceed to the next step. 

Hey, what's happening now? Well, the yeast will be making CO2 during the fermentation step. In fact, you will see bubbles form around the periphery of your SCOBY, especially if your SCOBY is as wide as your vessel. The SCOBY might even inflate just a tiny bit with the gas made by the yeast. You might be asking, so why don't we just do this step with the cultures in the bottles? Well, the answer is that this is a community of two microbes that depend on the action of the other. The yeast make CO2 and ethanol; the CO2 bubbles out in the environment, and the bacteria that live on the surface of the SCOBY eat the ethanol and make acetic acid from it with the addition of oxygen. In that way, the bacteria encourage the production of more of these compounds by the yeast. Also, the bacteria take some of the sugars in the solution and make and extrude cellulose, the stuff plants are made out of and the material that comprises the sturdy, gel like substance of the SCOBY. 

Step 5: Get fancy with an optional secondary fermentation

If you want to add more flavorings to your tea, this is the best time to do it. Place your chosen flavorings in each of the Mason jars and fill with 500 mL of komubucha from the main glass jar. Don't filter the kombucha at this point. Leave the Mother SCOBY in the main glass jar. This is now her permanent home. You can try multiple different flavorings or combinations. My favorite are: 

  • Anise: 1 tbs (~2 stars) per 500 mL
  • Dried hibiscus flowers: 1-2 tbs per 500 mL
  • Dried lavender: 2-3 tbs per 500 mL
  • Dried Dragonfruit;  1 tbs per 500 mL (mostly for the most beautiful color you've ever seen!) 

Let these infusions sit, covered with a paper towel and rubber band, for 24-48 hours. 

Step 6: Bottle it!

Take your Grolsch bottles and fill each with boiling water to clean. Empty the bottles after about 30 seconds and let the bottles cool to room temperature, about 40 minutes. Add 1/2-1 cup of unfiltered kombucha to each bottle, using a 1 cup ladle to assist, or carefully pouring from the glass jar if your lid isn't wide enough to allow a 1 cup ladle to dip into the tea. A funnel comes in handy here to aid in this process of filling the bottles. Then, place a fine mesh strainer onto the funnel, and fill the bottles with the rest of the kombucha, straining away the strands of culture. Fill the bottles up to 3 inches from the top. Cap the bottles and let sit at room temperature for 1 week, but do start checking the carbonation levels after 4 days, just in case you have an overactive culture! 

Caution: it is indeed possible for bottles to explode from the carbonation building up inside. In fact, I've had it happen. The mistake I made was using a very pretty bottle that was a 2 L capacity bottle. The problem? It was an ornamental bottle, not one that had ever in its lifetime held a carbonated beverage. Learning from my disaster, I'd recommend using bottles that are thick and ideally have held beer or another well carbonated beverage at some point in their history. These are much less likely to explode. If you're worried, you have two options. You can either place your bottles in a plastic bucket, or you can use plastic bottles, which might also explode but lack the whole sharp glass thing. Plastic won't carbonate as well, so I wouldn't really recommend it unless you are paranoid. 

Step 7: ENJOY. 

Once the bottles have gotten suitably carbonated, place them in the fridge. Ideally, you won't open all the bottles, because when they get cool they'll get more carbonated due to the fact that gasses are more soluble in liquids at lower temperatures. Keep in the fridge for up to two weeks. At this point, check the carbonation levels and taste. I usually don't have the issue of having bottles laying around. I tend to drink it up really quickly :)