All beers contain chemicals. So do we. Water is a chemical. I would assume the questioner is really referring to additions regarded as unnecessary, or substances produced in a laboratory rather than a field. In the former case, most of the 'big brewer' beers will contain things to preserve the beer, traces of finings (added to clear the beer), other grains and probably 'flavourings'. There's nothing wrong with using other grains. Batemans brew Combined Harvest, which is advertised as containing malted oats, malted rye, and malted wheat. It's good too, tastes clean, and has never given Baloo a hangover yet. Their Autumn Fall contains oats too. Also good. There's nothing wrong with substituting for the hops - hops aren't the be all and end all of beer. Heather Ale gets its bitterness from heather. Other brews may use gale. These aren't 'big brewer' things, though. I would love to have the ingredients listed like on other food products. And until we get this, it's almost impossible to say which beer has the most 'chemicals' in it. Smaller brewers are more honest about what goes in - and often have tours of their breweries (Cains in Liverpool for example). Anything passing CAMRA's scrutiny is unlikely to contain 'unnecessaries'. Unnecessaries from the drinker's viewpoint, that is. From the corporate accountant's point of view, additive adjusted brews give higher profits, as they give less wastage due to things going wrong. Just add beer flavouring, the punter won't notice....
http://www.morningadvertiser.co.uk/Drinks/Beer/Cains-takes-on-brewing-giants-with-cask-lager
(Cains brew something not many will have seen: cask lager - hand pulled not squirted from a pressure tap).
These references are to larger small brewers (i.e. not micro-brewers) to show that size isn't a bar to producing good beers. I could quote many more than these two.
