You may have seen it on the shelves in the supermarket or at your gym and wondered what the oddly named “kefir” was. This fermented dairy product has been a health staple in eastern Europe for years and is now a favourite of clean eaters as part of the trend for gut-friendly food. Pronounced “keff-fear”, it means “feel good” in Turkish.

The creamy, almost fizzy liquid is suddenly the focus of conversations at high-end gyms, while organic supermarkets are reporting that it is set to replace green smoothies and coconut water as this summer’s most sought-after refreshing drink. Sainsbury’s, Tesco and Ocado have announced a sharp rise in sales – “a staggering 112 per cent” in 12 months at Ocado, which recently added Biotiful’s Morello Cherry and Honey & Mint flavour kefir smoothies to its range ( 1.75 for 250ml).

The healthy fast food chain Leon sells blueberry and elderflower kefir smoothies ( 2.95), while the fashionable kefir brand Rhythm has 100ml shot bottles at 125 for five bottles (the idea is to use them to improve gut health in a short-term, intensive programme). Kefir can be an expensive habit.

At first glance the yoghurt-like drink looks uninspiring. So what is it that is causing such a stir? Proponents claim that it is an unrivalled aid to digestion and that it promotes a healthy gut. That may not sound sexy, but the benefits of a healthy gut are said to include weight loss, shiny hair and glowing skin. It is also said to have anti-ageing properties because it protects cells and reduces inflammation.

Gut health is just about the hottest topic in the wellness world, whether that’s talking about supplements like these sbo probiotics, or talking about food that naturally hosts good gut bacteria. You can indeed take supplements that will help you increase your gut health and improve your overall digestive system, but it is also important to consult a medical specialist before taking supplements like spore probiotic from websites such as Natural Healthy Concepts and others. In fact, scientists have found that things like kefir can also enhance the immune system. It has even been linked to good mental health. The idea is to drink kefir daily, first thing in the morning on an empty stomach, the theory being that it primes the gut lining to enhance the absorption of nutrients during the day. Proponents suggest starting with a few sips and gradually increasing your intake until you can manage a full 250ml glass.

Sales are growing fast at specialist healthfood stores too. They are up 34 per cent year-on-year at branches of Whole Foods Market. At Planet Organic you can buy Nourish Kefir smoothies, or the latest delicacy, coconut milk kefir. Dairy-free kefir water is also gaining in popularity, with products such as Purearth’s dairy-free kefir waters flying off the shelves.

However, it’s not only good for digestion. A single serving can provide about a fifth of our daily calcium needs, along with protein and B vitamins. Fans include healthy eating experts the Hemsley sisters and Liz Earle, the creator of the beauty brand that shares her name and bestselling author of more than 30 books on beauty and wellbeing issues. She describes it as “an essential food in any good-gut regime” and raves about its beneficial probiotic properties in her new book, The Good Gut Guide. “Kefir is packed with more powerfully beneficial probiotics than live yoghurt,” Earle says. “It’s also a good source of lactoferrin, a protein found in lactic acid, which helps to control inflammation, and it is especially helpful for controlling breakouts and even improving acne.”

The dietician Dr Megan Rossi, who is a research associate at King’s College London and a gut health specialist with a clinic in Harley Street, is also in favour of kefir as part of a healthy diet. “It does have a much wider range of bacteria than yoghurt,” Rossi says. What it lacks, she says, is clinical evidence that it is beneficial. “One trial found that consuming kefir for six months improved markers of bone health in a group with osteoporosis, and there are suggestions that it has anti- inflammatory properties,” she says. “But very few studies have been done on its uses and effects.”

It is also an acquired taste – a tart, creamy flavour that’s not initially to everyone’s liking. Earle admits that it “does tend to have the smell and consistency of sour milk”.

Rossi says that, like other trendy live-culture drinks, such as kombucha, kefir provides an array of bacteria that work to furnish the gut. Numerous studies have linked the traditional dietary practice of fermenting foods to positive mental health, which has led to a rise in popularity of German sauerkraut and the Korean fermented vegetable dish kimchi. “They all complement each other, and it’s hard to say one is better than the rest,” Rossi says. “As more work is done to investigate them, we may be able to compare the bacteria and suggest one food or drink for particular illnesses.”

Serious health nuts are making kefir at home. It’s easy, and relatively inexpensive to make. Simply pour water or milk over kefir grains (you can buy them at Lakeland or Whole Foods) cover and leave them to ferment at room temperature. “In both, sugar is needed for the fermentation process so you will either add sugar to the water-based kefir or the sugar in milk will do the job with dairy kefir,” Rossi says.

After 12 to 48 hours, remove the grains and set them aside. As for whether milk or water is better for you, Rossi adds: “There’s no evidence that one type is better for you than the other.”

DIY kits also come as live-culture kefir grains, which contain the most beneficial bacteria (up to 50 strains of yeasts and bacteria, including lactobacillus, the most widely known of the “friendly” bacteria), or as a freeze-dried pack. “I use it in a number of different ways – sipped on its own [great first thing on an empty stomach], as a base for smoothies or as a splash of ‘milk’ on muesli or granola. I even use it as a naturally ‘live’ skin cleanser and leave a layer on my skin at the weekends for smoother, brighter skin,” Earle says. “It’s become my fridge staple.”

How to make your own kefir
Kefir is most often made from cow’s milk, but it can also be made with coconut milk, coconut water or water. You’ll need a couple of large jars and a few muslin cloths, plus a pack of kefir starter grains (freeze-dried or fresh bacteria, which you can buy in Lakeland or in health-food stores) to make your first batch.

Ingredients for milk kefir
1 tsp milk kefir grains
250ml organic whole milk – or almond or soy milk

Method
1 Gently rinse the milk kefir grains with fresh milk or spring water and tip them into a sterilised glass jar. Pour in the milk and stir, using a wooden spoon. Loosely cover with the lid, so the gas that is produced can escape while it ferments, or cover with a cloth.
2 Leave it to stand at room temperature for 12 to 48 hours, until it sours to your liking. If you prefer, seal the lid and leave it to ferment in the fridge for a few days, which will take longer.
3 Stir the mixture, then pour it through a plastic sieve into a container. This is ready to drink, or you can leave it a little longer either at room temperature or in the fridge, releasing the lid occasionally to allow the gas to escape. If you find the taste too sour, flavour it with a little raw honey, maple syrup or some blended fruit.

If you don’t like milk, or can’t drink it, you can also make water kefir. Dissolve 40g cane/coconut/raw sugar in a small amount of hot water. Add this sugar syrup to 500ml pure, filtered water, add 2 tbsp water kefir grains, and put the lid on. Leave for 24 to 72 hours, stirring regularly. Strain through a plastic sieve and serve.