How 'the godfather of fizzy cabbage' Sandor Katz made us all love sauerkraut

• How to make sauerkraut like Sandor Katz

• Fermentation fundamentals: Dos and don'ts for beginners

• Probiotic products put to the taste-test

Live! Tonight! From a supermarket near you! It's trillions of microorganisms waiting to improve your gut health thanks to the power of fermentation.

Fermented food and drink products spruiking digestion-friendly bacteria have launched with increasing frequency over the past five years, but in 2019 the gut health market went properly gangbusters.

We could be keeping our children too clean and not giving them enough exposure to diverse bacteria.

Sandor Katz

Social media mentions of "gut health" are up 42 per cent in the past year, according to data from global food trends tracker Tastewise, while references to fermented food increased by 26 per cent over the same period. Rainbows of sauerkraut, kombucha, kimchi and kefir now colour the chilled sections of major retailers, joining an ever-expanding range of probiotic supplements, yoghurts and milks. Most notably, Australia's kombucha industry is now worth of more than $200 million – some feat for a slightly alcoholic tea that tastes like vinegar.

So, how did the "living" food and drink category become so popular? And what should consumers be mindful of when shopping for sauerkraut and its fermented, fizzy mates?

What's all the fuss about probiotics anyway?

The world has entered an era of functional eating in which foods are consumed with a purpose beyond mere sustenance. Tastewise reports that more than one-third of consumers are looking for functional benefits from their food, and the global functional food market is projected to reach $400 billion by 2025.

Hence, more collagen-rich foods are marketed for their anti-ageing properties; hemp oil is sold to help relieve stress; coconut water is advertised as a weight-loss aid; and products with live bacteria have migrated from health food stores to supermarkets.

"There's a lot of research supporting the fact we need more living foods for our health," says Sharon Flynn, founder of The Fermentary, which makes artisan pickles, sauerkraut and water kefir in Daylesford, Victoria. "Supermarkets are getting in on it because they're always trying to forecast trends."

Probiotics – that is, bacteria and other live microorganisms intended to have health benefits mainly by improving gut flora – have been linked to improved digestion, increased immunity, better heart health and, according to emerging evidence, even mental health.

Accredited practising dietitian and spokesperson for the Dietitians Association of Australia Melanie McGrice says there's a lot of clinical research still being done on the topic: "It is such an emerging field with new papers published on fermented foods every day. It's definitely one of the most popular topics of conversation within dietitian circles."

There are many types of probiotics with many different alleged benefits; they may be lab-grown and added to food (Activia yoghurt, say) or created naturally through fermentation.

Creating life through decay

American food writer Sandor Katz became the modern godfather of fizzy cabbage after his do-it-yourself book, Wild Fermentation, was published in 2003.

"Almost every individual, in almost every part of the world, eats and drinks fermented products every day such as bread, cheese, vinegar, beer, wine and soy sauce," he says. "Fermentation is already part of everybody's life."

Katz defines fermentation as the transformative action of microorganisms, but another way to think about it is the process of controlled decay. Leave a cabbage submerged in its own juices and salt for a few weeks and you have sauerkraut. Leave the same cabbage exposed to air on a benchtop for a month and you have something that might cause serious food poisoning. "There's certainly a fine line between fermentation and rot," Flynn says.

Wild Fermentation and Katz's 2012 follow-up, The Art of Fermentation, have become bibles for anyone wanting to know how long kimchi takes to develop depth of flavour and what the heck kefir actually is. (NB: Traditionally, kefir is a cultured, fermented milk drink, although many water kefirs now exist made with bacteria and yeasts feeding on carbohydrates instead of lactose. Sugar water, coconut water and soy milk are common kefir canvases.)

Katz will be in Australia from mid-February for a series of workshops and presentations in collaboration with Flynn and The Fermentary across 18 dates and five states. Only Elton John rocks more gigs on a tour Down Under these days.

The author believes increasing interest around fermentation owes a lot to a change in the public image of bacteria."Those of us born and raised in the 20th century never heard a positive word about bacteria," Katz says. "All we ever heard was how dangerous bacteria could be; how we had to avoid bacteria at all costs and destroy them with chemicals.

"I think the 21st century perspective has become a lot more nuanced in its understanding of the complexity of the community of organisms that reside inside us and its importance for our health. From an evolutionary perspective, they've been with us since the beginning."

A New Yorker article from 2010 states Katz believes "Americans are killing themselves with cleanliness". He explains this belief to Good Food Magazine, and says it can be applied to Australia, too.

"There's an immune stimulation after exposure to diverse bacteria," Katz says. "A lot of researchers are thinking about why we're seeing large rises in childhood allergies and asthma, and the most widespread conclusion is that it is because of a lack of exposure to bacteria.

"The jury is still out on this, but we could be keeping our children too clean and not giving them enough exposure to diverse bacteria, whether that's playing in the dirt or touching animals. It's called the hygiene hypothesis."

Savvy sauerkraut shopping

For people who want the benefits of bacteria through fermentation rather than rolling around in the barnyard, it's important to distinguish between "living" and processed foods.

"You can eat raw sourdough dough and get lots of live bacteria, but once that loaf bakes in an oven, those bacteria are no longer alive and you don't get the same benefits," Katz says. "That's not to say sourdough is bad – it's great – but you're not getting those live cultures."

Generally, bacteria will die when heated above 40C, as is the case with pasteurisation. "A can of sauerkraut from the cupboard might be delicious, but it's not going to contain any live cultures if it has been processed for shelf stability," Katz says.

For this reason, fermented products containing live bacteria will be found in a grocery store's chilled section. However, Flynn says shoppers should still check whether a refrigerated product has been processed. "I've seen American supermarkets place long-life milk in the fridge section, for example, even though it can exist on the shelf." Anything imported should be avoided, too, she says, as the products will likely be pasteurised before shipment and contain additional preservatives.

Purists should avoid products labelled with a list of the bacteria it contains – an indication that the bacteria has been grown in a lab and added later. Better still, give it a go at home (see below). Your gut will thank you.

Sandor Katz and The Fermentary events run February 18 to March 15 in NSW, Vic, SA, WA and Tas. Bookings at thefermentary.com.au.