Beer contains significant quantities of anti-oxidant compounds that might be expected to have positive effects on health. Some of these derive from the browning, Maillard reactions, occurring both in malting and during the boil. Some of these derive from hops, especially compounds called prenylated flavanoids like Xanthohumol. These hop antioxidants are polyphenols and they have been traditionally seen as having a negative impact on beer quality because they combine with peptides to cause haze in beer. Haze doesn’t affect the flavour, but it doesn’t look good and consumers don’t like it so the beer is filtered to remove them. Thus reducing the antioxidant potential of beer. Real ale is not filtered so more of these compounds remain in the finished beer. Also cask ale is often dry hopped. This is significant because, Xanthohumol, one of the promising antioxidant compounds, is not soluble in water, or CO2, but is soluble in alcohol. Large industrial breweries often use processed hop extracts in the boil and sometimes after the boil to provide the characteristic bitterness and hoppy flavour of beer. The extracts are typically manufactured by dissolving the hop compounds (alpha-acids) in liquid or supercritical CO2. Dry hopping is likely to result in higher levels of xanthohumol in the final product because the alcohol in finished beer allows greater quantities of xanthohumol to go into solution, and because hops are added at the final stage of the process the xanthhumol (and other prenylated flavonoids) are not driven off during the boil or lost to the yeast.
Of course, there is yeast in real ale, but this is also a likely net positive contribution to the nutritional value of beer as yeast contains a lot of B-group vitamins. Most B-vitamins in beer come from the malt, but the yeast takes some of these and uses them before they can be of much benefit to humans. If the yeast is filtered out, these vitamins are lost. They may look clear but bottle conditioned beers contain something like 1000 yeast cells per ml. (These are small numbers though for yeast. Normally yeast is pitched into beer at the rate of 1 million cells per ml per degree Plato of wort (which is a measure of the sugar content and therefore the potential alcohol content of wort)).
Finally, real ale has a lower carbon footprint than keg beer because it is served warmer. Refrigeration accounts for roughly 50% of the process costs at a large brewery (mostly due to chill filtering and cold conditioning of beer), and makes a significant contribution to the costs (and energy demand) on the retail side too.
So Hooray for Real Ale! It’s definitely the healthy green option.