From cheese to vinegar, throughout the centuries we have deliberately let - and even encouraged - food to go sour to enhance its flavour. But what is it that makes sourness such an enticing, complex element of the eating experience? And what are the best ways to harness sour flavours in your own kitchen? Mark Diacono sets out to demystify the sour world, and explore why everyone's extolling the virtues of kombucha and fermenting for their digestive health. By grappling with gooseberries and turning his hand to sourdough, experimenting with ultra-cool shrub cocktails, and making his own yoghurt, keffir and pickles, Mark tells the story of what makes things sour, and offers recipes that maximise the transformative power of this amazing taste.