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AutoBooch — Automate Your Kombucha Brewing System With a Raspberry Pi

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Tired of unpredictable brewing times for your kombucha? Worried about the health of your SCOBY pellicle? Look no further! The AutoBooch has your back!

Don't know what a SCOBY is? Have no fear—we cover that here.

A growing number of people drink kombucha, for a variety of reasons. Known by various names, such as 'mushroom tea' or 'Manchurian Mushroom,' the etymology behind the strange word is not definitively known. My favorite origin story comes from the legend of the Korean physician Kombu, whom prescribed it to the Japanese Emperor Inyoko, in the fifth century. Hence the word 'Kombu Cha': the tea of Kombu. I apply the se non è vero, è ben trovato rule and choose this one.

There are several purported health benefits, including probiotics, useful enzymes and malic acid and other beneficial acids, but there is no scientific consensus yet. I personally drink it because I like the taste.

However, the process of brewing kombucha is not the simplest, especially at first. Part of the problem is that the times for the primary and secondary fermentation stage can vary quite a lot, requiring regular testing to see if it has adequately macerated. This project helps make this part of the process more predictable by controlling the temperature using a Raspberry Pi, a relay, and a heating pad.

I'll sneak in a bit of science, and end with some pro tips for the adventurous.

First, you need to make the kombucha!

(I don't care about your hackneyed kombucha recipes. Get me to the automation stuff in Part 3!)

Step 1: Making a SCOBY From a Bottle of Kombucha

Picture of Making a SCOBY From a Bottle of Kombucha
SCOBY_comparison.png

The main engine for brewing kombucha is the interesting gloop of life-forms known as a SCOBY— a Symbiotic Culture Of Bacteria and Yeast. Technically, the floating part is known as a pellicle—the SCOBY itself is a complicated interaction, much of which occurs throughout the entire volume of the mixture (thanks to voxamps2290 for the clarification!)

The SCOBY pellicle is a complex, scabrous-looking, pad (or 'zoogleal mat') that floats at the top of the brew. The SCOBY as a whole consumes a sweet tea, and excretes a yummy, not very sweet, fermented beverage. The bacteria are various species of Acetobacter (mainly Acetobacter xylinum) and strains of yeast (one or more strains of Saccharomyces cerevisiae—Latin for 'sugar-eating beer fungus'—and Brettanomyces, Zygosaccharomyces, even sometimes Candida kefyr[1,2]) forms a colony within a bacterial matrix, forming a rubbery film that becomes thick and brown over time (and, if you get bored, you can turn into a fencing jacket). The yeast consume the sugar in the raw brew (usually black tea and sugar), producing a small amount of ethanol. In turn, the bacteria consume most of the ethanol and some elements of the tea (including a reasonable fraction of the caffeine). The ethanol is oxidized, creating acetic acid ('vinegar') and other acids (gluconic, lactic, and perhaps usnic and malic acid), as well as glucose and vitamins may be formed in various concentrations, although how much of each is still debated.

Symbiotic systems in general are very finely tuned. So engineering one of these puppies yourself is going to require a PhD in microbiology, a fully stocked biotech lab and a decade of dead ends (but then you could just battle malaria instead—your call). Failing this, there are three main ways to obtain a SCOBY yourself:

  1. Take a cutting from a friend/frenemy — literally cut a chunk of another healthy SCOBY.
  2. Purchase a SCOBY from a store or online (roughly $10).
  3. Grow one yourself from a bottle of raw, unpasteurized kombucha.

I'll run you through the last step, the most difficult path, padawan: growing one yourself.

You will need:

  1. One bottle of raw, unpasteurized kombucha (I used GT's Organic Raw Kombucha).
  2. Two bags of inexpensive black tea. Do not use tea with any added flavoring agents. Just pure black tea.
  3. A quarter cup of inexpensive white sugar.
  4. Large diameter, non-metallic, bowl with enough capacity for a couple of kombucha bottles. A pot for boiling.

Empty the contents of the kombucha bottle into the bowl.It should not be metallic, as ions can interfere with bacterial growth (looking at you, Chromium).

Boil enough water to fill the rest of the bowl (panel 1 in the figure above). Dissolve the sugar in the water, and add tea bags to make a sweet tea, removing bags when a rich color has developed. Allow to cool so that it is mildly warm to the touch. Pour into the bowl. Cover with a breathable cloth and store in a dark place for five days to a week, depending on the ambient temperature.

At this stage, a thin, yet strong, film should have formed on the top layer of the tea (see the panels 1 - 4 in the figure above). Repeat the above stage once or twice. The SCOBY pellicle should now have formed a fairly strong, thick matrix. Feel free to sample small amounts of the resulting tea. You will notice the flavor profile moving from a sweet tea, becoming drier until it becomes more acidic. You will notice a complex vinegary scent developing.

Eventually, you should end up with a healthy looking SCOBY pellicle. Name it something cool, like SCOBY-DOO, and post it all over social media. After time, noticeable layers form and it thickens greatly. There seems to be an entire cottage community devoted to 'SCOBY porn,' showing off large thick pellicles. Unfortunately, there are also common questions about rival bacterial growths on less healthy pellicles. There should not be black or wildly colorful growths on your pellicle (maybe see a doctor, too). You should aim for a finished pH of roughly 2.5 - 3.5, and try to keep your SCOBY in acidic conditions to protect it from invasive microbes, as it's a jungle out there. As with anything that may involve your health and safety: do independent research if you are concerned!

[1] Mayser, P. et al.: "The yeast spectrum of the ‘tea fungus Kombucha’," Mycoses 38(7-8): 289—295 (1995)

[2] Jarrell, J., Cal, T. & Bennett, J.W.:"The Kombucha Consortia of yeasts and bacteria," Mycologist 14(4):166—170 (2000)

Vitalij X1 year ago

Hi Ra,

Great answer(Devs of Instructables might add reply to an answer option aka answer to an answer).

> It's something of a monster now, very thick and leathery at the top with lots of tendrils at the bottom.

Thats a relief. I did the same thing, but when it's so big it have a great appetite - he eats sugar faster than i can add it and eventually it produces a lot of vinegar which destroys the taste of the drink. Now i keep pellicle max 10cm thick. And it needs around 2-4 days to produce light kombucha. As i use it substantionally for 2nd stage it's enough for me.

> However, I have seen a lot of photos of weird colorations, such as black, white or dark red mold on top, usually with the obligatory "Is my SCOBY OK?". I think the answer there is usually "no," but I don't know how to tell from just the color alone.

Same here. For me i decided that healthy color is the one it gets when it's young(top layer) or old(bottom layer): everything between #ffccXX - #ff77XX*. Sometimes i get more darker spots on top i suppose when it gets burned by undissolved crystals of sugar.

* the color i provided is approximate, but like you said light\dark brown.

> It also provides a physical barrier to the air, so the only exposure to the air is via the pellicle, so the only means of oxidation is via the bacteria in the colony matrix.

Thanks to you i have some new ideas now. Have you tried to keep the 1st stage jar closed(not fully, so it won't blow up, but enough to maximally limit access to oxygen? It's interesting how it will affect the taste of kombucha at this stage(...and SCOBY itself).

> If this is what you're after, what about a 'kegerator' or other carbonation system (one brand is 'SodaStream')?

Thank you for a tip, but i'm searching kind of a natural solution to keep things as simple as possible. I'll try idea with balloon on top of jar. Theoretically it will "breath" accordingly to pressure. Another problem is to get oxygen and keep CO2 inside at the same time.

> I find it hard to picture mentally because you want to limit exposure to oxygen, and retain pressure so the carbon dioxide dissolves adequately.

Totally agree to you, but i believe that solution exist we just have to find it).

> Yeast thrive on a little bit of protein. The best source of protein is... dead yeast.

Have you tried another sources of protein?

Best wishes,

Vitaly

Raro77 (author)  Vitalij X1 year ago

Hey Vitaly,
Some great questions.

> Devs of Instructables might add reply to an answer option aka answer to an answer

I'm with you there. I initially thought I screwed up my reply because it hadn't indented. Oh well, a work in progress I suppose.

> he eats sugar faster than i can add it and eventually it produces a lot of vinegar which destroys the taste of the drink. Now i keep pellicle max 10cm thick. And it needs around 2-4 days to produce light kombucha. As i use it substantially for 2nd stage it's enough for me.

Yep, I have certainly reduced my 1F brewing time substantially (but I do like it pretty vinegary). The good thing about paring your SCOBY down is that you can share it, or make other weird things with it. Or experiment with things like coffee etc. (never tried, but apparently it's a one-way street).

> Sometimes i get more darker spots on top i suppose when it gets burned by undissolved crystals of sugar

For me at least, the coloration comes from the tea itself, as I use cheap white sugar and make sure it's dissolved well. It's far from a supersaturated solution too, so I doubt I have crystallization.

> everything between #ffccXX - #ff77XX

Ha ha, nice! Spotted the web/full-stack dev ;)

> Have you tried to keep the 1st stage jar closed(not fully, so it won't blow up, but enough to maximally limit access to oxygen?

I *think* for the bacterial colonies to thrive, you require aerobic activity. Exactly how much, I'm not sure. That's the cool thing about the zoogleal mat, that it provides a somewhat impervious membrane.

As for closing it up, I already have problems with my guy's multiple escape attempts! No way I'm sealing my current set-up ;)

> Thank you for a tip, but i'm searching kind of a natural solution to keep things as simple as possible. I'll try idea with balloon on top of jar.

This would certainly work—as long as your balloon was "large" (i.e. ~pressure rated) enough. It's actually a neat mechanical fuse, as the balloon would pop before your vessel exploded. However, it would still be messy!

> Have you tried another sources of protein?

No I haven't. I'm a cheap-skate, and inherited this idea from brewing other beverages. You can purchase special yeast nutrient packs for wine and beer. These contain vitamin B, I think a little soluble magnesium, iron and protein. But the right protein profile comes from the residue of yeast itself, which nutritional yeast is the same species (although likely a different strain). Some brewers keep their own 'bug' going by topping it up a little. Where I live, the water is quite hard (a lot of dissolved minerals) so is naturally great for brewing.

Thanks so much for the discussion. Let me know how you go!
Cheers,
Ra

JonasI31 year ago

Hey there, great article. Very interesting. But I also realised after reading that I have seen this scooby thing a few times before. If I find a forgotten mug of tea down the back reaches of the workshop- there is this rubbery browny white thing floating. This gets hurredly discarded. Never knew it could be part of something potentially "healthy"

Raro77 (author)  JonasI31 year ago

Aha! It sounds like what you might have there is more of a COB—a Culture of Bacteria—than a SCOBY. An entirely different beast altogether. It would be better left as a scientific experiment than consumed. Although it still forms a zoogleal mat (sorry, I just love that term and try and use it frequently), it's from plain bacterial action on the milk from your tea.

If you're really lucky, it may be some Lactobacillus bulgaricus, Streptococcus thermophilus, or *chime sounds* the revered Lactobacillus acidophilus, and you could make yoghurt out of it. But I wouldn't count on it, and it's easy enough to make your own yoghurt without resorting to the ol' forgotten workshop mug.

Better off not risking food poisoning in the workshop, and stick to chucking it!

Vitalij X1 year ago

Awesome instructable! I recently found out a second fermentation stage just by accident(actually year ago, but who cares) and i thought it's cool, but after reading your instructable i see that there is still a lot to learn.

Could you, please, explain more about continuous primary fermentation. Your SCOBY pellicle is growing isn't it? How big(thick) do you keep it? And what do you do with remains? Do you keep the old one or new part of it?

I am wondering about dark brown coloration you have on pellicle - how old is it or what is it? I have little lighter brown coloration, but on downside of pellicle. Upwards it's clean and shiny, like everything around that dark spot.

Second fermentation stage is incredible and i enjoy it so much that i tried to remake it into continuous using jar with lid and spigot. But the problem is that i can't fully limit access to oxygen because i couldn't find adequately strong jar for such capacity(at least 4L). Maybe you know some method or tool like brewers airlock but with manual control of over-pressure level? It would be awesome to have fizzy drink in high volume.

Have you tested alcohol content in it?

Raro77 (author)  Vitalij X1 year ago

Hey Vitalij!
Good questions—I'm still learning myself :)


> Your SCOBY pellicle is growing isn't it? How big(thick) do you keep it? And what do you do with remains? Do you keep the old one or new part of it?

Yes, it grows in layers with each new batch. I have not done anything with it, just kept it au naturale. I wanted to keep the respective colonies in a high population in case any rival yeast or bacteria try to invade. It also provides a physical barrier to the air, so the only exposure to the air is via the pellicle, so the only means of oxidation is via the bacteria in the colony matrix. It's something of a monster now, very thick and leathery at the top with lots of tendrils at the bottom. But started as a wee guy, a thin layer in a bowl from a bottle of kombucha. However, it might be time to start sharing it, as I can't let it grow indefinitely!

> I am wondering about dark brown coloration you have on pellicle - how old is it or what is it? I have little lighter brown coloration, but on downside of pellicle. Upwards it's clean and shiny, like everything around that dark spot.

It's a complex interaction, but I believe light and dark brown, or beige, is fairly healthy. It has gotten darker with age, but I think part of the loss of translucence is because there are so many layers of material. I have only ever had successful primary fermentation, which is a little more than one per week for almost eight months now. However, I have seen a lot of photos of weird colorations, such as black, white or dark red mold on top, usually with the obligatory "Is my SCOBY OK?". I think the answer there is usually "no," but I don't know how to tell from just the color alone.

> Maybe you know some method or tool like brewers airlock but with manual control of over-pressure level? It would be awesome to have fizzy drink in high volume.

If this is what you're after, what about a 'kegerator' or other carbonation system (one brand is 'SodaStream')? Then you'll only be limited by the rate of your primary. Personally, my second ferment is faster than my primary, so it's the rate limiting step anyway. But, to answer your first part, I have no idea of a continuous 2F; I find it hard to picture mentally because you want to limit exposure to oxygen, and retain pressure so the carbon dioxide dissolves adequately.

> Have you tested alcohol content in it?

No. But I'd really like to!

Problem is, it's hard to tell using the specific gravity because the final products (both primary and secondary fermentation stage) are such complex mixtures. I have a refractometer, but the residual sugars and things like acetate throw it off. So that leaves mass spectrometry (which I don't have). Maybe that's another Instructable? ;)

Cheers,

Ra

richieacc1 year ago

Awesome instructable! I've tried my hand at kombucha a few times and always failed dismally. I don't think I've had my secondary fermentation right. How long do you keep it in that process? It looks like you have a brewer's airlock in there, so it's not a pressurised vessel? Is adding sugar optional in the second stage?

Raro77 (author)  richieacc1 year ago

Hi Richie!
Did you manage to get a SCOBY pellicle formed? This is a sensitive time, you have to have a bit of patience until you get the gelatinous layer forming.
Re: the secondary fermentation: to be honest, most of the time I don't use the brewer's airlock, as this doesn't give maximum effervescence. I usually use fully sealed glass containers that can handle a fair bit of over-pressure, and fill them almost to the top, to mimimize exposure to oxygen. The one you see in the photo here is banana, which I found tends to brew so violently that I use an airlock for it. Note that I'm pretty sure the alcohol content was a lot higher than other brews I've made. Be warned! ;)
Let me know if I can clarify anything further.

Raro77 (author)  Raro771 year ago

Oh, and I forgot to answer on the timing...
This comes down to your personal preference. If you like it drier and sour-er (which I do), then do the primary fermentation for longer. I do it for six days to a week. Secondary is usually well done in three days. You have to be very careful when opening the vessel (I sieve off the crud that floats to the top before refrigerating)!

Hi, Ra!

Thanks for the replies. I did get the pellicle formed. The flavour of my brew wasn't great, and it was flat, not fizzy enough. I think it may have been affected by UV, poor temperature control, and insufficient secondary brew time. Maybe even insufficient primary brew time.

A thought I had for the temperature control is to use an aquarium heater. They're quite cheap, waterproof, and have a built-in thermostat.

R

Raro77 (author)  richieacc1 year ago

Ahhh, I see. Well there are plenty of other variables!
For your primary fermentation, are you using plain black tea? And plain sugar? Is your vessel non-metallic?
Getting enough effervescence can be tricky. In that stage, you want the fermentation to be anaerobic, so fill your secondary vessels almost completely. Some people recommend 'burping'—periodic release of pressure by opening the caps, but I found that made my product weakly fizzy. Now I just let it go without looking at it. I haven't had an explosion yet (touch wood).

You definitely could use an aquarium heater. The only thing is that you have to figure out a way to get it to sit right in your fermenter (without interfering with your SCOBY pellicle) and then you have to clean it periodically. Another issue is that it's a centralised source of heat, so you have to be careful to not burn anything with it. The beauty of the brewing/propagating mat is that it's pretty gentle and the heat is distributed across the bottom. Funnily enough, the reason why my Raspberry Pi is located where it is in this Instructable is because one of its other duties is to automate the lights (still aren't happy with my automated fish feeding project :( ).

Raro77 (author)  Raro771 year ago

*automate the lights—in my aquarium :s

AidasJ1 year ago

Great job! I was going to do similar for Jun (should I call it Kombuchas grandmother?) and one for our beloved cashew yoghurt. Anyway, thank you for the Heat pad option, I'll definitely look at this. By the way, have you considered to use PID to have even more stable temperature? I know, it might be overkill but why not :D ?

Raro77 (author)  AidasJ1 year ago

Thank you!
I had to look up Jun tea. Looks very cool! Maybe if I get brave, I may try making it sometime too.

Yes, I had considered PID (partly because I haven't tinkered with PID control systems but would like to). However, the specific heat capacity is so high (4 litres of water, plus I keep the 2F vessels in thermal contact, so close to 8 litres) that sampling every half an hour means that the temperature profile tends to be very linear, so no need to integrate.

Unfortunately I only started logging the state of this guy in the last month or so (I made the system about seven months ago), so I can't give as rich a data-set as I'd like. However, I should display the performance data.

AidasJ1 year ago

P.S. For nonUS makers - adding a link to 220V heating pad below:

https://www.ebay.co.uk/p/Flexible-Heat-Pad-30cm-Di...

Raro77 (author)  AidasJ1 year ago

Thanks for that!
Would you mind if I link this in the article too?
Cheers,
Ra