Growing a Leather-like Biomaterial in the Classroom From Kombucha

BIOCRAFTERS!

Explore the emerging field of biomaterials hands-on by growing kombucha SCOBY (Symbiotic Culture of Bacteria and Yeast).

The SCOBY that floats on top of a jar of kombucha is an excellent introduction to biomaterials because it grows quickly and students can use the leather-like material for take home crafts. The dried SCOBY is surprisingly tough and flexible, but is also biodegradable. It and can be dyed, cut, formed, sewn, glued, sealed, or painted.

Great project for Biology classes (growth parameters of bacteria and yeast, cellular respiration), but tangents other STEM subjects (making skills, graphing data, design, etc.).

Students will:

• Understand the growth parameters of the SCOBY microorganisms.
• Grow the kombucha
• Harvest the biomass and dry it into a leather-like material
• Make things! (lanyard/ID holder, wallet, braided bracelets)
• Record data
• Discuss environmental impact of biomaterials

Project developed by Jon Simmons, at CrucesCreatives.org for STEAM in-class and after school programs.

SUPPLIES (Enough for 20 students to each get a ~16 sq inch piece of leather, scale to your needs)

(1) Bottle of Kombucha, fresh, raw, plain (OR even better get a starter from a local kombucha maker)

(8) Large food storage trays with lids (~100 sq inches of surface area each, 3-4 inches deep, must stack together tightly - see pic) [Target][Walmart], or Seed Flat sets might work [Amazon]

(4 gallons) Water, filtered, distilled, or "spring" (no chlorinated tap water)

(32 bags) Tea, black

(4 cups) Sugar, white

(2+) Cooling racks big enough to hold the SCOBYs for drying- plastic, plywood, or stainless steel, NOT aluminum or regular steel. The acidity will etch or rust those. [Amazon]

(1) Beeswax based sealer, liquid [Amazon]

(1) old cotton t-shirt or cotton jersey fabric (or optional carbon filter material below)

(1) Duct tape or hot glue to attach the fabric/charcoal filter [Amazon]

(4) Additional cloth scraps (~2"x2") or make-up sponges for rubbing in sealer [Amazon]

Patterns for cutting and punching leather

TOOLS

Tea kettle, electric, 1 liter/quart capacity [Amazon]

Heatproof container to steep tea, at least 1 liter/quart capacity [Amazon]

Drill [Amazon]

1/4" drill bit [Amazon]

Leather sewing kit [Amazon] OR Heavy needles and waxed thread.

OPTIONAL

• Charcoal filter material to reduce the vinegar/apple cider fermentation smell [Amazon]
• pH meter/test strips to graph how the pH changes as the SCOBY grows [Amazon]
• Dehydrator or oven, if you are in a very humid climate [Amazon]
• Laser Cutter to cut patterns
• Natural dyes, markers, or paints for adding design flare! [Amazon]

Links to shopping lists (coming soon!) [Amazon] [Walmart] [Target]

LESSON PLANS

RISD Biomaterials and more: https://biomaker.risd.edu/curriculum/full_curriculum.zip

Material analysis projects: https://www.sciencebuddies.org/science-fair-projects/project-ideas/GreenChem_p010/green-chemistry/vegan-kombucha-leather

To grow Kombucha SCOBY in our classroom we need:

• Darkness - We will store our culture away from direct sunlight or bright lights.
• Container - A container that is transparent so we can watch the culture grow, and has large surface area so it grows a large SCOBY. A plastic storage tub or food storage container will work great.
• Drinking Water - Bottled, Reverse Osmosis, or distilled water. Must be chlorine-free (no city tapwater). Well water might work if it is not contaminated with other organisms.
• Nutrients - Tea and sugar. Not a sustainable diet for humans, but actually provides what SCOBY microbes need.
• Air - The yeast in the SCOBY need some oxygen in the early phase of fermentation to break down the sugar, but then anaerobic (no oxygen) bacteria dominate in the second phase.
• Protection - We will use a cloth cover (or filter material) to keep out fruit flies and other microbes.
• Warmth - Kombucha will happily grow between 60-85F. Did I just attribute human emotion to a SCOBY? I don't know if they are happy, but they grow well at room temperature.

TEACHER - This is a great time to introduce the concept of cellular respiration [Khan Academy link]

• Each growing container will be a solid tray with a perforated tray inside it.
• Drill drain holes in the bottom of one of the plastic trays. Cover the entire bottom. This is how we will burp and harvest our SCOBY. The pattern of holes can be used to leave a pattern on the finished leather. More on that later...
• If you have access to a laser cutter, check out my laser cut version (pic)

• Cut a large section of the lid out.
• Use the cut out as a pattern to cut a larger piece of cloth or filter material. 1/2" larger all around is enough.
• Tape or hot glue the filter material to the lid. No holes! Fruit flies can bring mold spores and ruin the kombucha.
• Careful! Hot glue can burn you.

Kombucha SCOBY eats sweet tea. In biomaterial terms, we can call this tea the "growing medium".

I organized this process around a classroom setting. We need to make 4 gallons of sweet tea. If you have access to a kitchen stove and a large pot, follow this procedure:

• Take the kombucha culture out of the refrigerator so it can be warming up to room temperature while we work.
• Find the biggest pot you have.
• Add about 3 quarts/liters of filtered water to the pot and bring to a boil.
• Add 4 cups sugar and 32 tea bags
• Stir until sugar is dissolved. Cover the vessel so nothing jumps in there! A clean pot lid or towel will do the job.
• Let tea steep for 30 minutes.
• Add as much additional filtered water (up to the whole 4 gallons) as you can to the pot to cool the tea.
• When tea is barley warm (85F/29C or less), you can go to the next step.

If you only have a 1 liter electric kettle, follow this procedure to brew multiple batches:

• Take the kombucha culture out of the refrigerator so it can be warming up to room temperature while we work.
• Add 1 cup sugar and 8 tea bags to a heat proof vessel suitable for steeping the tea.
• Fill tea kettle with at least 1 quart/liter of filtered water and bring to a boil.
• Pour the hot water into the sugar/tea vessel and stir until sugar is dissolved. Cover the vessel so nothing jumps in there! A clean pot lid or towel will do the job.
• Let tea steep for 30 minutes.
• Add as much additional filtered water (up to the whole gallon) as you can to the vessel to cool the tea.
• When tea is barley warm (85F/29C or less), you can go to the next step.

• After the tea has cooled to room temperature remove tea bags and dispose of, or compost them.
• Pour the tea mixture (growing medium!) into the large food storage trays. Each batch of tea will fill one tray.
• Pour the remaining water into the trays, so each tray has about 1 gallon of liquid.
• Inoculate! Pour the store bought kombucha into the trays (or divide among the multiple trays). It is officially a living culture now.
• You want the liquid the be at least 1-1/2" (37mm) deep. Deeper lets you grow bigger SCOBYs.
• Make more tea to top it up if necessary.
• Stack the SCOBY Lifter tray inside the solid tray you just poured everything into.
• Put the filter lid on top, and now we wait...

The bacteria and yeast work together in a mutually beneficial arrangement. Because the sugar tea is a potential food source for any microbes nearby, the yeast and bacteria in the tea not only eat the available food, but also produce chemicals that are toxic to other microbes in a kind of microbial warfare. This particular SCOBY also creates a physical barrier that supports the community.

The yeasts eat sugars like fructose and glucose in the tea to produce ethanol and carbon dioxide (the gas that makes bread rise). Ethanol (i.e. alcohol) is toxic to many bacteria, but lactic acid bacteria don’t mind the ethanol. The bacteria prefer to eat maltose, meaning the yeast and bacteria don’t have to compete for the same food. The acid produced by the bacteria prevents other bacteria that can’t tolerate acidic environments from growing. The yeast, which thrive in acidic environments, in turn break down starches into simpler sugars that the bacteria and yeast can eat more easily. Together, bacteria and yeasts make an inhospitable environment for competing microbes and help make food for each other.

--image and text, Dr. Mary May and Dr. Aparna Nathan, https://sitn.hms.harvard.edu/flash/2020/wild-fermentation/

During fermentation, the yeast releases CO2 which forms bubbles under the SCOBY. To avoid large bubbles in the finished leather we need to burp these bubbles out.

Wait a week or so until a film begins to form. Then start burping the SCOBY every day. It's ok if you miss a few days.

Grasp the lip of the top tray (the SCOBY Lifter) and carefully pick it up out of the liquid.

Slowly... slowly place it back down into the liquid. We want to SCOBY to float, so don't push it under the liquid.

If the SCOBY separates, sinks, or growls at you, don't worry. We can try to squish out bubbles when we harvest and it might stick together as it dries. Everything is going to be OK...

You can feed a culture to grow another SCOBY after harvest. Just save a cup of liquid from the last harvest.

• Mix up a fresh batch of tea and let it cool.
• Pour 2 cups of the remaining kombucha from the growing tray into the cooled tea.
• Rinse the growing tray with water.
• Pour the fresh tea kombucha mixture into the growing tray and grow as before.
• As long as no mold, insects, or UFOs (Unidentified Funky Objects) are present you can keep the SCOBY factory rolling!

A 1/2" thick SCOBY will dry to a very thin, but strong, floppy, flexible leather.

A 1" thick SCOBY will dry to an 1/8" thick, very tough leather.

• Work near a sink or outdoor water spigot.
• Use the SCOBY lifter tray to lift the SCOBY out of the tub. Let it drip a few seconds.
• Rinse the SCOBY under tap water and wipe off any loose bits. Hold it together if it is splitting into sheets.
• OPTIONAL - Brush on some food dyes, now or at any stage of drying.
• Lay the SCOBY on a drying rack, or a sheet of plywood or plastic. You can leave it on the SCOBY lifter tray for the first few days and it will have the texture of the tray embossed in the finished leather. OR you can plop it out directly onto the drying rack (or a sheet of plywood). It's going to look cool no matter what.
• After a few days, peel it off and flip it over.
• It will probably take 3-5 days to dry depending on thickness, airflow, and humidity. You can use a dehydrator or put it in direct sunlight to speed things up.
• You can stop the drying process from floppy to crispy. The final finishing (wax) will effect this, too.
• What about forming? Yes, you can dry it over a form and it will retain the shape.

You grew a thing!

Your new SCOBY leather can be:

• Cut with scissors
• Cut or etched with a laser cutter (the etching comes out lighter than the original color)
• Punched
• Sewn (use heavy needle and large thread)
• Riveted (or screw-post)
• Dyed, painted
• Embossed with a roller type embossing tool. [Amazon]
• Glued (white glue, wood glue, or any glue that claims to work with leather should work)

Here are some patterns I have used: (I'm still adding links here)

• Mystery braid bracelet https://www.youtube.com/watch?v=41gFIbhYaM0
• ID holder/Lanyard
• Pouch/wallet https://www.craftpassion.com/wp-content/uploads/2016/01/no-sew-leather-pouch.pdf
• Simple wallet https://cdn.shopify.com/s/files/1/0029/0396/5760/files/WALLET_TEMPLATE.PDF?v=1597260651
• Airpod case cover

Using makeup sponges or scrap cloth, rub some beeswax finish into both sides of the SCOBY. Let it soak in for a while and then wipe off any excess beeswax. Let it dry again, maybe overnight.

Some people have pressed the waxed leather with a hot iron for 10-30 seconds. I haven't tried that, yet.

The field of biomaterials seeks to replace conventionally manufactured materials with biologically grown materials which can have many advantages.

"...Leather tanning and finishing is an environmentally harmful aspect of leather production... Historically, common tanning agents included brain, urine, and tree tannins. Today, the most common tanning process is chrome tanning, which is favored for its quick turnaround and lower prices. 

During chrome tanning, the hide is soaked in a chemical bath which includes chromium (III) as the tanning agent. If not managed properly, chromium (III) can oxidize into chromium (VI), an extremely toxic chemical. Many smaller tanneries in rural areas do not have the wastewater treatment capabilities to manage these harmful toxins. The effluent is therefore released into local communities where it pollutes waterways and poisons groundwater. In these communities, workers suffer from skin diseases and other illnesses as a result of being exposed to toxic water.

Chrome-free tanning and vegetable tanning similarly soak hides in a chemical bath to prevent degradation. However, instead of using chromium as the tanning agent, chrome-free tanning often uses aldehydes. Vegetable tanning replaces the tanning agent with bark or plant tannins. 

While these alternative tanning methods appear more sustainable by replacing the harmful chromium tanning agent, these other methods still use chemical baths that contain a myriad of other ingredients which can be released into the local water supply. Life cycle analyses of these three different tanning methods do not show a significant difference in the degree to which they negatively impact the environment. " -- https://bucha.bio/bulletin/what-is-the-environmental-impact-of-the-leather-industry

How is "Leather" grown from kombucha cultures different from conventional leather processing?

There is a lot of research and tinkering to be done, across many career fields, to bring the dream of biomaterials to reality. Whatever you are interested in, consider how biomaterials or biofabrication might solve a problem, or upcycle waste, or protect soil, air, and water.

1. If you leave the kombucha long enough the SCOBY will consume all of the liquid. This might be a tidy way to get a predetermined thickness by mixing a certain amount of growth media and ignoring it for two months. Will report back.