DIY Kombucha - Bacterial Cellulose Fermentor

Are you a kombucha amateur? Are you interested in sustainable design? Well, here is something you might like! This DIY Kombucha - Bacterial Cellulose Fermentor will allow you to combine the possibility to enjoy some freshly home-brewed kombucha while having fun growing your own bacterial cellulose: a material that, once properly washed and dried, looks like faux-leather!

As a biodesigner, I have worked with bacterial cellulose for several projects in the past. With some other fellow designers, we noticed the impossibility to preserve the liquid culture of fermented tea while growing bacterial cellulose: the mix of bacteria and yeast in the liquid consumes all the sugar in the mix, turning the good kombucha into a terribly acidic juice. However, collecting the cellulose earlier in the fermentation process isn't good either as the cellulosic membrane growing on top of the liquid (also called kombucha mother or SCOBY - Symbiotic Culture Of Bacteria and Yeasts) isn't thick enough to be manipulated and used after the drying process (as it dries, it looses a lot of its mass and volume).

This co-producing fermentor bridges the gap between the two production processes as it allows you to transfer the liquid culture into a separate fermenting tank, while refilling the main culture tank.

In this Instructable, you will learn how to make your own Kombucha - Bacterial Cellulose Fermentor using 3D printed parts, elements from hydroponic cultures and reclaimed soda bottles. This tutorial will also cover the basic principles to start your own kombucha culture and all the protocols related to the use and maintenance of the fermentor.

This prototype was completed in the context of the research project titled "The Fabrication of a Kombucha Machine", was conducted at the Milieux Institue for Arts, Culture and Technology (Concordia University, Montréal QC). Principal Investigator Ann-Louise Davidson, SSHRC SIG grant.

Fermentor Structure:

• Computer with Cura
• 3D Printer
• PLA spool
• Small hand tools (scrapper, tweezers, small cable cutter, etc)

Note: if you don't have your own printer, look for the nearest fablab or maker space around you. Also check with your local institutions (schools, universities, libraries) if they can help you print your parts!

Fermentor Tanks:

• (x2) - Transparent 2L soda bottles
• (x1) - Transparent 1L soda bottle
• (x4) - 1/4" plastic barb
• (x4) - 1/4" plastic elbow
• (x1) - Aquarium air pump kit (with air pump, check valves and clear vinyl tubing)
• (x1) - Aquarium safe clear silicone adhesive sealant
• (x1) - Facial tissue, paper towel or a 6"x6" piece of fabric
• Battery powered drill
• 5/32" diameter drill bit
• Cutter
• Measuring tape
• Cutting mat

Kombucha Culture:

• 1 Black tea bag
• 50g of white sugar
• 50g of brown sugar
• 200mL kombucha starter
• 1L of tap water
• 2L bowl
• Funnel
• Isopropyl alcohol or rubbing alcohol
• Kettle
• Nitrile gloves
• Paper towel
• Spoon
• Scale
• Waxed paper

The structure of the fermentor is composed of the following elements:

• (x1) - Base
• (x6) - 220mm long column
• (x6) - 200mm long column
• (x2) - Bottle support
• (x9) - Small connector
• (x3) - Long connector

All these elements are available here, and can be directly imported in Cura.

The following details about the 3D prints are relative to the machine I used (in my case Creality CR-10 S5 printers with a 0.6mm nozzle and PLA from Prusa). Results may change depending on the 3D printer you use, the quality of your PLA or your preferred print settings!

The base (x1) and the bottle supports (x2) were printed with basically the same settings, here are the key parameters:

• Standard quality: layer height 0.2mm
• Wall thickness: 1.2mm
• No gaps between the walls
• Infill: 10%
• Infill pattern: Gyroid
• Connect infill lines: yes
• Printing temperature: 215ºc
• Bed temperature: 50ºc
• Print speed: 50mm/s
• Initial layer speed: 20mm/s
• No support
• Build plate adhesion: 2 lines, 5mm distance skirt

The columns were printed with a Creality CR-10 S5 printers with a 0.4mm nozzle and wood infused PLA from an unknown supplier. Again, results may change depending on the 3D printer you use, the quality of your PLA or your preferred print settings!

The 170mm columns (x6) and 240 columns (x6) were printed with the same settings, here are the key parameters:

• Standard quality: layer height 0.24mm
• Wall thickness: 1.2mm
• Wall lines: 3
• Top/Bottom pattern: Zig Zag
• No gap between the walls
• Infill: 0%
• Printing temperature: 215ºc
• Bed temperature: 50ºc
• Print speed: 60mm/s
• Initial layer print speed: 15mm/s
• No support
• Build plate adhesion type: skirt
• Skirt line count: 2 lines
• Skirt distance: 1mm

Note: If you plan to print several parts at a time, I suggest you to use the One at a Time print sequence option (in the Special Modes section) and make sure to position your parts with enough distance from each other on the build plate.

The connectors were printed with a Prusa i3 MK3 printer with a 0.4mm nozzle and PLA from Prusa. Again, results may change depending on the 3D printer you use, the quality of your PLA or your preferred print settings!

The long connectos (x3) and short connectors (x9) were printed with the same settings, here are the key parameters:

• Standard quality: layer height 0.25mm
• Wall thickness: 1.2mm
• Wall lines: 3
• No gap between the walls
• Infill: 5% (no infill)
• Infill pattern: Grid
• Printing temperature: 210ºc
• Bed temperature: 50ºc
• Print speed: 50mm/s
• Initial layer print speed: 20mm/s
• Support: no
• Build plate adhesion type: Brim
• Brim line count: 10

Note: If you plan to print several parts at a time, place your parts close to each other so the brim of each part fuses with the other, making one large common brim for all the parts.

Assemble the structure as shown on the diagram and following this order:

1. Base (x1)
2. 220mm long columns (x3)
3. Short connectors (x3)
4. 220mm long columns (x3)
5. Long connectors (x3)
6. Bottle support (x1)
7. 200mm long columns (x3)
8. Short connectors (x3)
9. 200mm long columns (x3)
10. Short connectors (x3)
11. Bottle support (x1)

The kombucha-bacterial cellulose fermentor is composed of three tanks:

• The refill tank (2L soda bottle)
• The primary fermentation tank (2L soda bottle)
• The secondary fermentation tank (1L soda bottle)

Each tank will be previously washed with soapy water, rinsed, dried and the sticker removed. Save the caps for the next step!

The bottles used for the refill tank and the secondary fermentation tank do not require any action, just keep them as they are. However, the bottle used for the primary fermentation tank need to be cut at the bottom to enable you to harvest the cellulose mat. As shown on the picture, a thin line is visible at slightly above the bottle "feet". Follow this cutline with a cutter or a pair of scissors and make sure to have a straight cut. Save the bottom of the bottle as it will be later used as a cap to maintain the filter.

Note: some soda brands use bottles with a bottom wider than the body. This is very handy for the primary fermentation tank as the cut line is more visible and easy to cut and it also makes it much easier to use for holding the filter. Be mindful about this detail when choosing your bottles!

The refill tank cap needs to be adapted as explained here:

1. Using the drill with the 5/32" diameter drill bit, drill two holes in the cap (centered but not too close to each other)
2. In each hole, install the 1/4" plastic barbs: use the threaded side of the barb and bolt it in the hole from the outer side of the cap
3. Cut one 1" long piece of vinyl tubing and plug it on one barb (outer side of the cap).
4. Cut one 4" long piece of vinyl tubing and plug it on the other barb (outer side of the cap).
5. For the 1" long tubing side, prepare and plug the following assembly: 1/4" plastic elbow + 1" long vinyl tubing + 1/4" plastic valve + 1" long vinyl tubing + 1/4" plastic elbow.
6. For the 4" long tubing side, plug an aquarium check valve, cut and plug a 8" long piece of vinyl tubing on the other side of the barb (inner side of the cap).

Note: if the 8" long vinyl tubing is to large for the barb, try a smaller tube (1/8" diameter).

The primary fermentation tank cap needs to be adapted as explained here:

1. Using the drill with the 5/32" diameter drill bit, drill two holes in the cap (centred but not too close to each other)
2. In each hole, install the 1/4" plastic barbs: use the threaded side of the barb and bolt it in the hole from the outter side of the cap
3. Cut one 1" long pieces of vinyl tubing and plug it on both barbs.
4. On one side, prepare and plug the following assembly: 1/4" plastic elbow + 1" long vinyl tubing + 1/4" plastic valve + 1" long vinyl tubing + 1/4" plastic elbow.
5. For the other side, plug a 1/4" plastic valve.

Only the refill tank and the primary fermentation tank are directly connected to each other through their caps. The secondary fermentation tank cap does not require any operation and will be used as it is to close the bottle and allow the carbonation of the kombucha.

Once the silicone sealant is dry, it is time to install and connect the tanks.

1. Cap the refill tank (with the 8" inside the bottle) and place it on the top bottle support (bottom up).
2. Cap the primary fermentation tank and place it on the bottom bottle support (cut side up).
3. Cut a 6"x6" piece of fabric (or use a facial tissue) and place it on top of the cut side of the primary fermentation tank. Hold the fabric in position using the other part of the bottle (install it like a cap).
4. Cap the secondary fermentation and place it standing at the centre of the base.
5. Align the tubing system so the plastic elbows are facing each other.
6. Measure the distance between the elbows and cut a vinyl tubing at the measured distance.
7. Connect the two elbows.
8. Place the aquarium air pump nearby the machine and measure the distance between the refill tank check valve and the air pump.
9. Cut a vinyl tubing at the measured distance and connect the check valve to the pump.

The machine is now complete and ready to be used! Before using the machine, it is advised to check for any leak. Test each tank with water and observe if there is any water dripping. Use the silicone sealant to fix the issue (and wait for another 24h before the next test).

Now, let's go through the production procedure!

Note #1: As we are now working with the kombucha culture, it is important to work in a clean environment (such as a kitchen) and on a clean work surface. Make sure to wear gloves and sanitize your gloves and tools with Isopropyl Alcohol before touching the culture!

Note #2: If you already possess a kombucha culture at home, jump to the next step.

Note #3: Place your fermentor in a clean space, away from direct sunlight as the UV rays are harmful to the microorganisms in the kombucha.

A week before the first use of the fermentor, prepare your kombucha starter that will be used to inoculate the fresh tea. This step only needs to be done only the first time, or if your kombucha culture becomes contaminated by molds, yeasts or fungi, and needs to be replaced.

Here is how to make your kombucha starter:

1. Get a kombucha mother (scoby), either online or from a friend. If you get your mother from a friend, make sure the culture it comes from looks healthy: good smell, no visible mold on the surface and with a nice, thick and homogeneous mat of cellulose floating on the liquid surface.
2. In a clean 1L glass container, pour 500mL of boiled water.
3. Add a bag of black tea.
4. Add 25g of white sugar and stir with a spoon.
5. Add 25g of brown sugar and stir with a spoon.
6. Wait a few minutes and remove the tea bag.
7. Let the mix cool down to room temperature.
8. Add the kombucha mother and its liquid.
9. Cover the container with a piece of fabric or paper towel.
10. Let it ferment for a week.

The quantity of starter will be more than enough for the machine, take good care of the excess of starter as it will become your backup culture in case of a contamination issue. You can also use it to brew more kombucha or share it with your friends so they can brew their own kombucha!

Once the starter is ready, it is time to make your first batch of tea for the fermentor. Remember to keep working in a clean environment, wear gloves and sanitize your gloves and tools before touching the culture. The recipe is basically an upscaled version of the starter:

1. In a clean 1L glass container, pour 1L of boiled water.
2. Add a bag of black tea.
3. Add 50g of white sugar and stir with a spoon.
4. Add 50g of brown sugar and stir with a spoon.
5. Wait a few minutes and remove the tea bag.
6. Let the mix cool down to room temperature (in the meantime, check the next step to prepare the fermentor).
7. Add 100mL of liquid from your starter (make sure to filter the mother that formed over your starter).

Note: a simple way to remember the proportions of ingredients, regardless of the quantity: you need 1 volume of sugar (half brow/half white) + 10 volumes of boiled water + 1 volume of kombucha starter.

While the tea is cooling down (before the inoculation), clean the refill and primary fermentation tanks, caps and tubing systems of the fermentor with warm soapy water, rinse them and let them dry. Make sure to remove the check valve before cleaning and make sure the 1/4" plastic valves are open to drain the soapy water out of the tubes.

Note: Before using the equipment, I tend to suggest sanitizing all surfaces and inside the tubing systems with Isopropyl Alcohol and rinse them. Do it a few minutes before use so the alcohol can evaporate.

Now, it is time to fill the refill tank:

1. With a funnel, pour the tea in the tank.
2. Close the tank, making sure the 8" vinyl tube is inside the bottle.
3. Check the valve is closed and the check valve is properly plugged (air must go in the bottle, not the other way).
4. Connect the check valve to the aquarium air pump.
5. Turn the air pump on and wait the bottle to feel hard when squeezed with your hands.
6. Once the tank is pressurized, turn the pump off and unplug it from the check valve. (leave the valve on the tank!)
7. Position the refill tank, upside down, on the top support of the fermentor.

Now, let's install and fill the primary fermentation tank:

1. Position the cap and tubing system on the primary fermentation tank. Make sure all the valves are closed.
2. Place the tank, cut side up, on the bottom support of the fermentor.
3. Make sure the fabric filter in placed and secured on the tank.
4. Connect the 1/4" plastic elbow from the primary fermentation tank to the the plastic elbow on the refill tank.
5. Open the 1/4" plastic valve on the refill tank.
6. Open the 1/4" plastic valve connected on the primary fermentation tank.
7. Filling the fermentation tank will take a few minutes. You will see air bubbling in the refill tank due to the air suction caused by the pressured being released. If you notice a lack of pressure from the refill tank, replug the air pump air turn it on to maintain the pressure.
8. Once the liquid is almost fully transferred, start closing slightly the plastic valve on the fermentation tank side to slow down the transfer speed. Once the final drops of liquid are about to reach the valve, shut it down to stop the transfer and to prevent the liquid to flow back in the tubing.
9. Unplug the refill tank from the fermentation tank valve.
10. Wash the refill tank and the tubing system with soapy water and let it dry until the next cycle.
11. Let the culture ferment for a week.

After a week of fermentation, it is time to partially transfer the kombucha culture from the primary fermentation tank to the secondary fermentation tank. You might be able to see that a thin translucent cellulose sheet has formed on top of the culture: it is your bacterial cellulose mat and you must be careful to keep it healthy and afloat!

Here is the transfer procedure for the secondary fermentation tank:

1. Clean your secondary fermentation tank following the protocol explained in step 12.
2. Place the bottle, standing open, under the primary fermentation tank, at the centre of the base.
3. Make sure the purge valve of the primary fermentation tank is aligned with the bottle neck of the secondary fermentation tank.
4. Open the purge valve.
5. The liquid level will start to move down with the cellulosic mat still floating on the surface. When you see the cellulose coming close to the level of the support bottle, turn off the valve to stop the transfer. It is important to stop the transfer before the cellulose reaches the narrow part of the bottle, otherwise it will be deformed and will sink in the liquid.
6. Take the secondary fermentation tank out of the base and cap it.
7. Repeat steps 11 - 12 - 13 to continue the production cycle.

After 4 weeks, or 4 transfer cycles, your bacterial cellulose mat should be thick enough to be harvested (it should be between 5-10mm thick). In the meantime, check your culture is healthy (no strange smell or contamination) and that no gas bubbles are trapped under the cellulose mat. If you see bubbles, gently remove the primary fermentation tank from the support and very carefully, slightly tilt the bottle on one side to release the trapped gas.

During the secondary fermentation process, kombucha amateurs add sugar and fresh fruits or spices to give flavors to their home made kombucha. The secondary fermentation should take a few additional days. You can taste your kombucha to know when it is ready: it really depends on your preference, do you like it sweet or do you like it sour? When you think it is ready, put the bottle in the fridge so it is ready to be served. Make sure to drink it before the next transfer cycle, or have another bottle ready for it.

Feel free to check online kombucha recipes for more tips and inspiration!

Cheers!

IMPORTANT NOTE: If you ever feel sick after drinking your kombucha or if it looks or smells strange, STOP drinking it and purge your whole batch of kombucha! It may be contaminated with bacteria, fungi or yeasts and there is no way to fix it. In case of a doubt, never drink something you are not sure it is safe!

After 4 cycles of transfer-refill, your kombucha mother should be thick enough to be picked-up! It is also a good time to go through a general maintenance of the fermentor. Here is the procedure to pick up the cellulose:

1. Transfer the liquid culture in the secondary fermentation tank, normally, as explained in step 15.
2. In another clean container, pour what is left in the primary fermentation tank and save it as a starter for the next cycle, or empty the whole batch in the secondary fermentation tank.
3. Pick up the cellulose mat
4. Gently wash the cellulose in soapy water to remove the brown filaments of yeast and the sugar.
5. Leave it in the soapy water for several minutes.
6. Rinse it with clear water.
7. Let it soak in clear water for several minutes.
8. On a flat surface, place a sheet of waxed paper so the cellulose won't stick while it dries.
9. Lay down your cellulose on the waxed paper (or any slightly greased surface) and make sure there are no air pockets trapped under.
10. Let it dry at room temperature for a few days.

Note 1: As we regularly add new sweet tea in the primary fermentation tank, the cellulose sheet is loaded with sugar very difficult to dissolve. I find it pretty effective to boil the scoby in a pot on the stove for about 30 minutes to wash the cellulose in depth. Boiling the scoby is also a way to pasteurize it and to reduce its vinegary smell.

Note 2: Bacterial cellulose changes very quickly depending on the moisture level in the air. If the ambient air is very dry, your cellulose will be very crispy and easy to break. On the other hand, if the moisture level is high, the cellulose will be soft and maybe sticky.

Once your kombucha mother is collected, it is suggested to go through a general maintenance of the machine. Simply unplug and wash all the tubing, valves and tanks in soapy water, rinse them and let them dry. As you reassemble the fermentor, check that everything is in good condition for the next batch.

Once your bacterial cellulose is dried, it is totally up to you to play with it! Bacterial cellulose feels like faux-leather and can be easily sewn, laser cut and engraved, glued, ground, press-dried, etc. You can grow multiple cultures at the same time in order to gather more cellulose sheets faster, or you can even grow large sheets in much bigger containers (if you don't mind losing your kombucha culture).

Bacterial cellulose has been used by artists, designers, bio-engineers for several years now, yet it's full potential hasn't been completely discovered: food packaging, sustainable fashion, bioart, projection screen, print media, biophilic architecture, biocompatible scaffold for tissue engineering, biodegradable films, etc. Maybe you'll be able to develop a new application for it while playing with it!

This fermentor was originally designed for bacterial cellulose and kombucha culture, but its design allows for much more! Why don't you try growing algae inside? Or maybe mushrooms? Can the tubing system between the tanks can facilitate hydroponic culture? Well, it is up to you to discover it! Feel free to test new things, to improve the design of the fermentor, to make mistake and most of all to share your experience with it!

I truly hope you enjoyed this Instructable and I am really excited to hear from you and your experiments!

Théo C.