How to ferment vegetables

What is fermentation?

Fermentation promotes the growth and life cycle of good bacteria to transform the flavour and shelf life of ingredients.

All vegetables are covered in the good bacteria lactobacillus and, when you slice up, grate and squeeze vegetables with salt, they release their juices, which mingles with the salt to create a brine. Once contained within this briny environment, lactobacillus multiplies and begins to break down the ingredient, digesting the natural sugars and transforming them into lactic acid, which creates the tangy flavour and a sour environment that keeps the growth of nasty bacteria at bay.

While products like kimchi, kefir and kombucha have only become trendy in the UK in more recent years, people have been harnessing the natural process of fermentation all over the world for thousands of years.

As many people are cottoning on to the appeal of naturally fermented food, it’s becoming less scary, and something we increasingly want to do for ourselves at home, rather than relying on industrially produced versions. Many of these have been pasteurised and therefore are no longer ‘alive’ or as health-giving or flavourful. Beginning with fruit and vegetables is a good introduction.

Top tips for fermenting and pickling vegetables at home

1. Pickling or fermenting?

Pickled produce brings acidity to a dish and fermented brings salt, so it’s all about balance, what you serve them with and how you want the dish seasoned. Both methods are straightforward, but an easy pickle can be as simple as some sliced red onion steeped in vinegar and a touch of sugar for a few minutes to soften. Health-wise, pickled foods don’t hold the same benefits as fermented.

2. Safety first

The most important thing, whichever recipe you go with, is that your jars need to be properly sterilised. You can run them through the hottest setting of your dishwasher, but some domestic washers don’t wash at a high enough temperature, so if you want to be really sure your jars are sterilised, steam them or wash well and dry them in an oven at 150C.

3. Jarring

The only extra kit you really need, other than ingredients or what you already have in your kitchen, are glass or ceramic jars – never plastic or metal. You can reuse and sterilise old jars, but if you are buying them new, the best jars are made by Le Parfait. We prefer the straight-sided screw-top style over the classic Kilner style because, when you are fermenting, you need to release the natural gases that build up and a Kilner jar traps it in too tightly.

4. Storage

Store ferments in a cool, dark place such as a pantry, utility room or on a shelf out of direct sunlight.

5. Burping

Because of the gas produced by the good bacteria, it’s a good idea to burp the jars (lift the lid/muslin) every few days so that they don’t run the risk of exploding.

How to sterilise your jars

You can buy special preserving jars, but you may have glass jars knocking around and reusing them is a great way of cutting down on waste. You’ll need wide-mouth jars (such as old pickle jars) to pack in all the ingredients, and it’s really important to sterilise your jars to avoid the growth of the wrong sort of bacteria, which could make you ill. Use 500ml jars for these ferments.

• To sterilise them, heat oven to 180C/160C fan/gas 4.
• Wash the jars and lids thoroughly in warm soapy water, then leave to dry on the draining rack, drying the lids with a clean tea towel.
• Put the jars on a shelf in the oven for 15 mins, then remove with oven gloves.
• Once cool, they are ready to use.

Read our guide for more detailed instructions on how to sterilise jars.

How do I know when the ferment is ready?

Trust your gut – taste as you go and you’ll soon figure out how far you want to take a ferment. It should be pleasantly sour and not smell bad. If you’ve decided that it’s tasting funky enough for you after a few days, just put it in the fridge – this will halt the fermentation. Keep an eye (and nose) on your ferments, and also watch out for any mould. If you see or smell a ferment starting to go bad, or if it tastes unpleasant, don’t take any risks – just discard it.

How long do fermented vegetables keep for?

Kept at a consistent cool temperature away from daylight (basically in the fridge), pickled and fermented vegetables should keep for at least three months, if not longer. Fermenting vegetables will need the jar burping occasionally. A bit of white bloom on your preserve is fine, but anything that looks like mould or anything green is an indicator that it’s not sterile and it’ll need throwing away.

The brilliant thing is that it’s very simple to do at home – all you need are some sterilised jars, vegetables, muslin, baking parchment and a bit of patience.

Where can I read more about fermenting?

Pickling can be done by taste – you just need good vinegar, sugar, salt and vegetables. Fermenting requires a bit more intel. A book that covers everything from the science and safety to health benefits, as well as being a great recipe book, is The Art of Fermentation by Sandor Ellix Katz. Seriously, for him it’s a way of life.

Fermented vegetable recipes

Try your hand at fermenting your own food at home with these easy to follow recipes.

Kimchi

Try our classic kimchi or, if you are short of time, our quick kimchi is a speedy option. Use this spicy fermented cabbage in a range of delicious Korean-style recipes, from kimchi fried rice and kimchi sesame udon noodles to kimchi cheese toasties.

Sauerkraut

Follow our easy recipe for how to make sauerkraut using raw cabbage, or try our radish kraut variation. It's delicious served in salads, hot dogs and burgers as well as with sausage and mash. Or, for a classic Eastern European take, use it to fill these pierogi dumplings from Olia Hercules. Also read about the various health benefits of sauerkraut.

Fermented wild garlic or spring onions

Make the most of seasonal spring vegetables by fermenting foraged wild garlic or spring onions. These punchy ferments are perfect for adding to toasties, cold meats or fried egg on toast for a full-flavour brunch.

Discover more fermented foods...

Homemade kefir
How to make kombucha
Funky fermented ginger lemonade
Miso recipes
Chilli tempeh stir-fry
Sourdough starter
Tempeh traybake

Have you tried fermenting food at home? Let us know in the comments below...

Good Food contributing editor Rosie Birkett is a food writer and stylist. Her cookbook, A Lot on Her Plate, is out now (£25, Hardie Grant). Follow her on Twitter and Instagram @rosiefoodie.

Formerly head chef at Ottolenghi’s Nopi restaurant, Ramael Scully is chef-owner of Scully St James’s in central London, where he focuses heavily on preserved produce.