Rachel De Thample says she experienced a “massive wave of energy” when she started drinking kefir, a fermented dairy drink, on a daily basis. It was not long after giving birth to her son, when she’d started to feel “wiped out” all the time.

Blaming a poor diet growing up in the US, combined with “a lot of antibiotics” she’d taken as a child, De Thample cut out sugary and starchy foods and embarked on “a pretty pure diet, mostly fruits and veg and nuts and a few lean meats and fish.

“Then after I did that for about six weeks, I started to introduce loads of fermented foods to repopulate the good bacteria – the one I first started with was goat’s milk kefir from Wales,” she recalls.

After enjoying the energy “rushing back”, Texas-born De Thample decided to have a go at making her own kefir, which is how her obsession with all things fermented began.

Now, the 44-year-old, who started out as a TV news journalist before moving to the UK and making the switch to food writing and training as a chef, has penned River Cottage Handbook No.18: Fermentation, imparting all the knowledge she’s garnered throughout the years.

So what exactly is fermentation? “Basically, you’re creating an environment where good bacteria can multiply,” De Thample explains. She’s keen to stress that you don’t need to get bogged down in the science if you want to create tasty fermented foods like pickles, sauerkraut and sourdough bread, or drinks like kefir and kombucha.

“I try to explain enough of the basic science in the book, without being too off-putting, because it put me off initially. I just thought, I need, like, a degree and I need a sterilised kitchen and I need special tools – then I realised that all I needed was a jam jar, a pinch of salt and cabbage to make sauerkraut.”

Kombucha recipe
(Makes 1 litre)
4 tea bags or 4tbsp (level) loose-leaf tea (black, green, white or herbal)
1L boiling filtered water
85g raw, organic caster sugar
1 kombucha scoby
2tbsp kombucha from a previous batch, or 2tbsp apple cider vinegar
You will also need:
A 1.5L jar or jug, for fermentation
Cheesecloth or a clean tea towel
Bottles, for storage
Fermentation time:
5–14 days

1. Brew the tea with the boiling water in a heatproof jug, allowing it to steep for 30 minutes to one hour. Strain the tea into the jar or jug, then whisk in the sugar until dissolved (I tend to ferment kombucha in a Kilner-style jar).

2. Once your tea has cooled to room temperature, add your scoby. Pour in the two tablespoons of kombucha or apple cider vinegar – this helps to kick-start fermentation; add more if you want to speed up the fermentation (or brewing) process.

3. Cover with a clean cloth and leave to ferment at room temperature (18–22°C) for five days to two weeks.

4. Strain the kombucha through a cloth-lined sieve into a jug. Pour into bottles and seal with corks or stoppers. Leave at room temperature for 24 hours to build up carbonation. Then keep in the fridge until ready to drink, or for up to six weeks; the longer you leave it, the tangier it will become.

Seasonal kombucha or jun flavours:
Blend the kombucha with 150g fresh fruit, one tablespoon of spice or a large handful of the herb, and an extra one to two tablespoons of sugar to taste. Strain through a cloth and pour into bottles. Seal and ferment at room temperature for a day before placing in the fridge. For optimum flavour, drink within one month. These are some favourites.

Spring: Blood orange and cardamom

Summer: Strawberry and rose petals; redcurrant and bay; apricot and thyme

Autumn: Blackberry and lavender; pear and chamomile; fig and rosemary

Winter: Cranberry, fresh ginger and star anise

River Cottage Handbook No.18: Fermentation by Rachel de Thample, photography by Gavin Kingcome, is published by Bloomsbury Publishing.