Brewing kombucha at home is more straightforward than most people expect, and genuinely enjoyable. With the right temperature, clean technique and accurate quantities, the result is an aromatic drink that shows exactly how real fermentation works. What a SCOBY does in detail is covered in What is a SCOBY? This article is about the making.

What you need

• Green and black tea (decaffeinated or heavily flavoured teas work poorly, the culture needs the nutrients from real tea)
• White sugar (refined household sugar; honey or heavily processed sweeteners can disturb the culture)
• Filtered water
• A glass vessel, at least 1.5 to 3 litres, with a wide opening
• A SCOBY with starter liquid
• A breathable cover: cloth or coffee filter, secured with a rubber band
• Swing-top bottles for the second fermentation

Use glass only, not ceramic. Glazed ceramic can release lead from the glaze through the acidity in kombucha. Clean the vessel with hot water rather than washing-up liquid, since detergent residue can harm the culture.

Quantities per litre

The sugar is food for the culture, not a sweetener for you. Most of it is consumed during fermentation.

Step 1: prepare tea and sugar

Measure tea, sugar and water using the table above. The tea brings the aroma, the sugar gives the culture its energy.

Step 2: steep sweet tea at 82 °C

Heat half your water to around 82 °C, the ideal temperature to extract tea without drawing out bitterness. Stir in tea and sugar, steep for 12 to 15 minutes and make sure the sugar dissolves completely. You are making a concentrate that you dilute with cold water afterwards.

Step 3: bring to 24 to 28 °C with cold water

Remove the leaves or bags and add the remaining water. The temperature should now sit between 24 and 28 °C, the ideal range for the culture. Never add the SCOBY to hot liquid: above 30 °C it can be damaged, and too cold means fermentation starts sluggishly or not at all.

Step 4: add the SCOBY

Pour the diluted tea into your glass vessel. Add the SCOBY and the starter liquid. Cover, secure with a rubber band, and place it somewhere warm and undisturbed out of direct sunlight, ideally at 20 to 28 °C.

Keep it clean

Fermentation needs cleanliness, not sterility. Wash your hands thoroughly, clean glass and utensils with hot water instead of detergent, remove any residue completely, and do not work next to plants or compost. The breathable cover lets air through while keeping fruit flies and dust out.

First fermentation

• Days 1 to 3: the yeasts start working, producing CO2 and the first aromas.
• Days 4 to 7: the bacteria follow, forming fine organic acids.
• Days 7 to 16: the longer you wait, the drier and more acidic it becomes. Taste from day 7 with a clean straw.

When it tastes the way you like it, the first fermentation is done. Take out the SCOBY, keep 10 to 20% of the liquid as starter for the next batch, and bottle the rest.

Second fermentation: flavour and carbonation

Fill your kombucha into swing-top bottles, add fruit, ginger, herbs or spices to taste, and seal them. With no contact to the air, carbonation builds because the CO2 cannot escape. Leave the bottles at room temperature for 2 to 5 days, then open them carefully over the sink, as pressure can build considerably. After that they belong in the fridge, where they keep for several weeks and fermentation slows down markedly.

What can go wrong

• Mould: dry, fuzzy patches in green, black, blue or pink on the surface. Discard the batch completely, clean the vessel thoroughly and start again. Not to be confused with brown yeast strands, which stay wet and are normal.
• Foul rather than sour smell: if it smells of acetone or genuinely unpleasant rather than vinegary, discard it.
• Still too sweet: fermentation was too short. Give it another day or two.
• Too sour or too dry: fermented too long. Shorten the time next round or work at a cooler temperature.
• No bubbles in the second fermentation: usually too little residual sugar or too short a rest.