Back in 1975 the number of ales produced each year by commercial brewers worldwide was measurable in single figure thousands. Today, the closest we can get to an accurate estimate is somewhere between a quarter and half a million.

Thus far most of the consumer revolt over beer has been about ales. The more obvious reason for this is that traditional ales are easier to produce than authentic lagers, in particular because there is no need for lengthy cold-conditioning. The less obvious reason is that ale yeast are capable of producing firework displays of flavours in contrast to lager yeast’s military parade.

What surprises beer drinkers in the 21st century is the extent to which the wave of new-new-new types of beer represents a return to brewing as normal, which is to say before the Prohibitionist tendency and the First World War intervened.

The array of ales that now exists is so huge that in order to follow the differences a wide range of styles needs to be understood. We could have tried doing this by colour, listing White, Blond, Pale, Amber/Red, Brown and Black types, but decided against this as too many styles now span the divides between these.

Equally we could have tried organising this by beer style cluster – listing pale ales, then porters, then barley wines and so on – except that the overlaps and cross-breeding of styles would have caused too many confusing difficulties at the boundaries.

We thought about listing styles by country of origin, but soon realised that the borders between nations are fluid over time and that what historical allegiances are agreed rarely fit neatly with current national identities.

So instead, for now at least, we have ordered the ales primarily by strength, along the lines of session, sampling and sipping beers, defined by intent rather than by fixed and rigid percentages. We have then added special sections to cover Porters & Stouts, Wheat beers, Farm-Brewery styles, Spontaneous & Mixed Fermentation beers, and Regional specialties. By adopting these somewhat oblique distinctions we hope we have made a necessarily contrived listing look like a rather more neat and orderly way of seeing things than the subject perhaps deserves.