Ferment: The Life-Changing Power of Microbes

by Tim Spector

**As seen on Channel 4’s What Not to Eat**

‘A super healthy and tasty gift for you and your gut microbiome – discover the joy of fermenting’ Dr Clare Bailey Mosley

From the world-leading gut scientist and no. 1 bestselling author of Food for Life, comes an introduction to the life-changing benefits of fermentation.

Of all the ways to prepare food, fermenting is surely the most mysterious, miraculous and misunderstood. As Tim Spector shows in this groundbreaking book, the science is now clear that adding fermented foods to our diets brings an astonishing range of benefits for our health.

Drawing on his own cutting-edge research, and including practical tips for buying and making fermented foods, Tim demystifies the world of ferments, and introduces us to some of his favourites – from homemade kombucha and kefir, to sourdough, miso and coffee.

He explores the extraordinary science of fermentation and the transformative role of microbes, in our kitchens and in our guts – and reveals why fermenting is the key to good food and good health.

Ferment is the ultimate gift for anyone who wants to eat better and feel better.

Praise for Tim Spector:

‘One of the visionaries leading the way. His writing is illuminating and so incredibly timely.’ Yotam Ottolenghi

‘No fads, no nonsense, just practical, science-based advice on how to eat well’ DAILY MAIL

‘Tim Spector has been exploding the myths around food and health for years’ THE TIMES

‘The man changing how we eat’ TELEGRAPH

Genres: Nonfiction, Food, Science, Health, Cookbooks, Biology

309 pages, Kindle Edition

First published September 11, 2025

About the author

Tim Spector is Professor of Genetic Epidemiology at Kings College, London and Director of the TwinsUK Registry, which is one of the worlds richest data collections on 11,000 twins. He trained as a physician with a career in research, which since 1992 has demonstrated the genetic basis of a wide range of common diseases, previously thought to be mainly due to ageing and environment. Most recently his group have found over 400 novel genes in over 30 diseases, such as osteoporosis, osteoarthritis, melanoma, baldness, and longevity. He has published over 600 research articles in prestigious journals including Science and Nature. He coordinates many worldwide genetic consortia and is currently at the forefront of research with a highly competitive European Research Council Senior Investigator award to study Epigenetics – a new exciting research area into how genes can be altered. He is the author of several books for the scientific and public communities and presents regularly in the media.

Reviews

[K.J. Charles]

Reasonably persuasive on the importance of eating lots of fermented food. I'm currently fermenting garlic in honey because he really pushes that one, we will see how that goes.

[Niki · Rating 4 out of 5]

I enjoyed reading this as an avid fermenter, and there are a couple of recipes I will add to my already (some might argue) excessive fermentation repertoire. Marked down because as with all Tim Spector’s books he quotes a lot of unpublished studies, states a lot of opinion as fact and I worry that everyone believes everything that he says (because he’s a prof) without questioning any of the evidence.

[Laura Haynes · Rating 4 out of 5]

I picked this up to learn more about gut microbes and the science behind fermented foods. The science-y sections were really interesting and explained the benefits of different foods. I also loved that Momo Kombucha got a shout-out, as it’s something I buy from time to time, so I was glad to see it make the cut!

But most of the book is recipe-focused, and I’m just not someone who’s going to ferment things at home… I’d rather spend the money buying good fermented foods than make them myself, so a lot of those sections weren’t really relevant for me. So, I enjoyed the educational side but didn’t get much use from the DIY recipe!

[Mariella · Rating 4 out of 5]

nice little book dedicated to the topic rather than being lumped in with general health eating advice. personally enjoyed the deep dive into the individual ferments with recipes and some of Tim's anecdotes from a past life. some readers may have wanted more labouring of the science and referencing. it was enough to convince me to have a go!

[Jonas · Rating 3 out of 5]

Some good and forward thinking ideas, but too focused on climate worries and self promotion via ZOE

[Kirsty · Rating 4 out of 5]

A great resource into gut health and the future of fermentation to create non-meat foods and more medical compounds (so far only insulin).

What I like about all of Tim’s books is the hours of real life experience, experimenting, and research that goes into making them so you get the condensed version.

Tim is honest about the medical research still being in it’s infancy but there’s a lot of indicators that we should be embracing more fermented food. It makes perfect sense that our ancestors would have eaten more fermented foods, then our current modern diet, to get through the leaner months.

He’s preaching to the converted but ferments can be time consuming so I personally prefer a single ferment. I already make Milk kefir, which is a simple single ferment which I keep in constant production as I enjoy it every day with breakfast. But when I made water kefir, although an amazing replacement for fizzy drinks which I miss (IBS), having to constantly burp in the second fermentation was a pain and non-adherence caused messy explosions. I also experimented with sourdough from scratch last year but thought the resulting taste didn’t justify the time or mess, but I might have another whirl with an already mature starter.

Based on my experience and time, the book’s recipes for single ferments I’m looking forward to making are: kimchi, tomato ketchup, and the honeyed garlic. I’ll probably have a crack at Kombucha at some point until I get bored with how much time it takes up.

[Andrew Westle · Rating 4 out of 5]

As someone who makes sourdough, has fermented all sorts of things over the years, and tries to include fermented food in my diet, this book felt both affirmation and gentle prod.

The core argument is persuasive, microbes are good for your gut and gut health is good for all health. Not in a wellness-trend way, but in a fundamental, human way. But fermentation is not just about gut health. It is about connection to time, to process, to food that is alive.

There are moments where the book leans heavily into Zoe, and at times it reads a little like an advert. That is a shame, because the underlying principles are strong and make sense without the branding. Some sections are firmly rooted in science; others feel more speculative. I guess this is the part of where this field sits, emerging, evolving, still being understood.

The recipes at the end are refreshingly simple. They lower the barrier to entry. No mysticism, basically just jars, salt, patience.

What stayed with me most was the cultural irony. Fermented food now feels like a middle-class lifestyle pursuit, something aesthetic and curated. And yet it used to be ordinary, ordinary and necessary. A way of preserving abundance and surviving winter. Slowing down, making food at home, working with microbes rather than against them, none of this is new. But this is something everyone can afford, because it’s something people can make themselves and with some ease.

[Tamsin · Rating 4 out of 5]

This book did for me what I really value in a non-fiction read: it made me make changes in my life and see things differently. In this case, I actually made my own sauerkraut and yogurt before even finishing the book.
That being said, for a book by a scientist, there were some unconventional parts, such as giving vague units in the recipes like 'makes 1 jar' and some instructions seemed ambiguous to me. I was also sometimes confused with the seemingly contradictory health advice, it's better to keep it straightforward and not muddy the waters with too much information. Also, he very much goes all in on the acidic fermented foods and skims over the downsides of eating tons of salty acidic cabbage. Finally, there are a lot of subtle and unsubtle plugs for Zoe products.

I do overall have a positive impression of the book, but would urge everyone to always keep their critical thinking hats on while reading (anything really), especially when you consider making lifestyle changes.

[Albert Valiente · Rating 5 out of 5]

Is a nice book, not comprehensive, not systematic, but nice.
I’m skeptical about his opinion on the benefits of alcoholic fermented foods but at least he put an effort on saying POTENTIAL. What bugged me the most is (1) how he generalized the effects of neurotransmitters like GABA on our phisiology when the reality is much more complex; and (2) how he reproduced the old myth of not using metal materials to ferment, without questioning it. These metals are non reactive alloys unlikely to interact, not saying impact, on the quality of ferments.

[Jordan · Rating 3 out of 5]

This was Fine. I've always loved fermented and pickled foods, though lately I've been getting into making them myself more, so I thought this would give me a good understanding of what actually happens during the process to make them so Good. It was an interesting read, and a good start for dipping toe into the benefits, history, and some science of fermented foods. However it did feel like one long subtle ad for the author's company, ZOE.

[Anita · Rating 2 out of 5]

Will rate a 2 as for me personally I wouldn't dare make anything from book.
It was interesting but not as helpful for me as the last book I read by Tim
' Food for life ' or something.
Yeh didn't really learn anything I dont already know.

[J.T. · Rating 3 out of 5]

Good information about a variety of topics, but more focused on the science than being a hands-on volume. The audiobook is a solid long-form podcast, but I find Sandor Katz's books on the topic far more useful.

[Alex · Rating 5 out of 5]

Easy to read, split into three sections; general information about fermentation and it's benefits, specific information about the different types of ferments and finally recipes. Informative, easy to read with good tips on how to increase the amount and quality of fermented food in your life.

[Lauren Morgan · Rating 5 out of 5]

Love that is has recipes

[Edward Bunker · Rating 3 out of 5]

would recommend getting the physical version.

[Clare Staines · Rating 4 out of 5]

Good book to keep coming back to. Needs another edit. Spaces are missing in one spot and I think tablespoons were mistakenly used rather than teaspoons in one of the kombucha recipes

[Sam · Rating 4 out of 5]

Very useful book. I liked all the science behind different sorts of ferments and recipes easy to follow.

[Hari · Rating 4 out of 5]

Drinking kefir everyday since reading this book.