Making Kombucha

Goal

I recently discovered that I like the flavor of Kombucha and that it might be a healthy, probiotic drink if the residual sugar can be minimized. The commericial Kombuchas that I have tried are too sweet, and rather expensive as well. I decided I would make my own to experiment with getting a higher conversion of sugar to vinegar than usual. I’ve also been interested in finding a non-sucrose way to brew the Kombucha, because sucrose is a disaccharide of fructose and glucose, and fructose is one of the unhealthiest sugars, so I would rather any residual sugar not be fructose. Yeast preferentially ferments glucose over fructose, and so fructose would likely be the source of residual sweetness.

What is Kombucha

Read the Wikipedia article or Cultures for Health article for details, but briefly Kombucha is the result of fermenting sugar tea with a symbiotic culture of bacteria and yeast (SCOBY) that results in the sugar being converted into alcohol by the yeast, and the alcohol being converted into acetic acid (vinegar). Secondary fermentation in a sealed glass bottle can make it a fizzy drink when the CO₂ produced by the fermentation is retained in the bottle.

While the details are given below, basically I do bulk fermentation of sugar tea for 14 days, and then bottle with a 12.5% addition of fruit juice for a 14‑day secondary fermentation.

Cultures For Health is an excellent source of information about Kombucha. I recommend their many pages of information on it, which may be found at Cultures for Health > Learn > Kombucha. Another good website with information is Kombucha Kamp.

Equipment

I have ended up with a fair amount of Kombucha-specific equipment for this project. Here is what I use [most prices updated October 2023]:

• Semi-specific to Kombucha project
  • 2 Filters for wide-mouth mason jars, $7 ea
  • 4 Half-gallon wide mouth mason jars, $6.25 ea
  • 1 Kenley Fermentation Carboy Heater with Thermostat , $50
    [but thermostat failed after 3.5 months and I had to replace with Inkbird ITC-308, $35]
  • 4 Stick-on thermometer strip, $2 ea
  • 1 3" Fine Mesh Strainer, $5
  • 24 Swing Top Bottles w/Caps - 16.9oz, $3 ea
  • 1 Initial SCOBY, $19
  • 1 pH Indicator Strips, $5
• Optional
  • 4 Kombucha brewing lids for mason jars, $10 ea (or use cheesecloth)
  • 1 Distiller, $280 (optional)
• General Kitchen stuff (which I already had)
  • 1 Kitchen thermometer with alert, $65 ea
  • 1 8‑quart stock pot
  • 1 Cheesecloth for covering and straining, $6 ea
  • 1 Kitchen scale, $47
  • 1 Non-metal funnel, $6 [no longer available]
  • 1+ Wide mouth quart mason jar, $3 ea

Some of these items I already had for other purposes (such as one filter for making cold brew coffee, stock pot, funnel, kitchen scale, kitchen thermometer, quart mason jars). So basically I spent around $200 to equip myself for making Kombucha. I will probably take about four months to break even given the above.

The quart mason jar is helpful for rehydrating a purchased SCOBY, if you get one that way, and for experiments with small batches.

If the distiller is included, then the cost is significantly higher, around $450. Not counting the electricity it uses, the distiller itself will take 16 months to break even on compared to buying a gallon of reverse osmosis water each week, but it is much more convenient. With the cost of the electricity to run it, the distiller never breaks even, so it is entirely about convenience. The distiller turns out to be useful for more than Kombucha as well (e.g. tea and coffee, soy milk). I use it every night, and buying seven gallons of water a week would be inconvenient. I could never go back to just filtered water in the kitchen after seeing the residue left behind in the distiller. I also insist my water be kept in glass or stainless steel, not plastic, which rules out many water options.

I hope that someday I can replace the distiller with a product from Water Harvesting Inc. to pull moisture from the air to create pure water.

Ingredients

Each 7 days I use:

• 200 grams (7.1 oz) of glucose powder, about $3.60
  (organic cane sugar would be just $0.49)
• 24 grams (0.85 oz) of oolong tea, about $7.84
  (or Peets Ti Kuan Yin, about $3.63)
• 2.43 L (10.3 cups) of chlorine-free (reverse-osmosis or distilled) water, about $0.50
• 250 mL (8.5 floz) of organic pomegranate juice, about $3.80

This results in five bottles of Kombucha, for a cost of about $8.42-$15.74 per week, or $1.68-$3.15 per bottle. (I should probably use a cheaper tea, but it is one I buy for drinking as well.)

I also use a small amount of organic white vinegar to clean the distiller, but the cost of this is tiny. Vinegar is also called for when rehydrating a purchased SCOBY.

Culture for Health Formula

For reference here are the Cultures for Health Kombucha Ingredient Ratios and the Kombucha Kamp Easy Recipe:

† 2 cups preferred

In metric this would be approimately, with my formula appended:

† 480 mL preferred
‡ Adjust amount to target 400 grams (14 floz) per bottle

Method

Note: I do everything in mass (grams) instead of volume (e.g. mL or L). This is because my kitchen scale is more precise than any of my beakers.

I brew my Kombucha for 14 days on a heating mat set to 23.5–24.5°C (74–76°F). I divide it into two sets of two half-gallon jars. (This provides some redundancy in case something goes wrong with one, but that has never happened.) Two jars are processed on even weeks and two jars on odd weeks. This yields about 2250 mL (9.5 cups) of flavored Kombucha a week (2000 mL of kombucha tea, 250 mL of fruit juice), or five bottles of 450 mL (15 floz).

On Friday night, distill a gallon of water to use in the morning.

On Saturday morning, create glucose tea from distilled water, tea, and glucose. My yield is 89% sugar tea from the water I start with due to evaporation, spillage, etc., so the distilled water needs to be about 12% more than the desired sugar tea. (Fermentation yield after 14 days is also about 89% of the sugar tea plus starter.) Plan for it take a few hours for the sugar tea to cool to fermentation temperature. While the sugar tea is cooling, strain the 14‑day old kombucha, and set some aside as starter for the next batch. For the secondary fermentation combine kombucha and pomegranate juice and bottle. When the sugar tea is cool, mix with starter to fill two half-gallon brewing jars. This is explained in more detail below:

1. Put 24 grams (0.85 oz) of tea into the two filters (12 grams (0.42 oz)—3 tablespoons—each).
2. Heat 2420 grams (2 quarts 21 floz) of distilled water in stock pot to tea brewing temperature — 90°C (194°F) for oolong, 100°C (212°F) for black tea.
3. Add filters with tea to stock pot. Set timer to 5 minutes.
4. After 5 minutes of brewing tea, add 200 grams of glucose powder, and stir to dissolve.
5. Set thermometer to alert when sugar tea temperature falls to 29°C (84°F).
6. Decant two half-gallon jars of 14‑day fermented Kombucha through cheesecloth and plastic strainer(s) into temporary containers (I use a one gallon jar). The fermented tea should no longer be sweet, but instead fairly sour. If not, you may need to ferment longer or at a higher temperature. If you have pH test strips, you can test the fermentation that way (it should be 2.5 – 3.5).
7. Remove SCOBYs from their containers and rinse the jars.
8. Each jar will probably have two SCOBYs: the original, and the new baby SCOBY. Discard the least healthy-looking SCOBYs (or give to someone who wants to start their own kombucha production). Put 200–250 grams (400–500 grams total) of kombucha into each of the new half-gallon jars. You can substitute white vinegar if there is not enough fermented tea. I vary the amount of starter so that the remainder is 2000 g. Typically it is around 480 grams (2 cups 0.9 floz).
9. Move previous weeks’ five flip-top bottles to refrigerator.
10. Add 250 grams (8.8 floz) of pomegranate juice to the kombucha. Set out five 500 mL (17 floz) empty flip-top bottles. Using the scale and either a non-metal funnel or glass beaker, pour 450 grams (1 cups 8 floz) of flavored Kombucha into each bottle. Set these bottles on the heating mat to ferment for another two weeks to covert some of the pomegranate juice sugar into fizz. The pomegranate juice contains about 6.4 grams (0.23 oz) of sugar per bottle, which will fuel the bottle fermentation.
11. When sugar tea has cooled to approximately 29°C (84°F), fill each half-gallon jar to approximately (or just below) the 1500 mL (6.3 cups) mark (about 1.2 L of addition to each, or 2.35 L combined). Add a SCOBY to each jar.
12. Put the two half-gallon jars back on the heating mat and let brew for 14 days.

I observe that the 2420 grams (2 quarts 21 floz) of water, 24 grams (0.85 oz) of tea, 200 grams (7.1 oz) of glucose, and 480 grams (2 cups 0.9 floz) of starter will yield about 2800 grams (3 quarts 2.8 floz) pre-fermentation, and 2480 grams (2 quarts 23 floz) post-fermentation. This results in 2000 grams (2 quarts 6.5 floz) of unflavored kombucha for bottlig and 480 grams (2 cups 0.9 floz) of starter for the next batch. Adding 250 grams (8.8 floz) of pomegranate juice yields 450 grams (1 cups 8 floz) per bottle. This is a bit less than the 475 mL (16 floz) in a supermarket product like GT’s.

A total of 232 grams (8.2 oz) of sugar was the input to the two stages of fermentation, or 46 grams (1.6 oz) per bottle; how much was converted to alcohol and vinegar is uncertain. Commercial Kombucha (e.g. GT’s) contains 16–20 grams of sugar per bottle; I hope mine is much less.

References

• The Art of Fermentation: An In-Depth Exploration of Essential Concepts and Processes from Around the World, by Sandor Ellix Katz.