Steam aside - which not having an effect on the flavour of Porter, we do not intend to discuss here - there was one final innovation that affected Porter brewing, and also contributed to its demise. This was the attemperator.
Essentially a coil inserted into the fermenter through which cold water was passed, it was a means of controlling the fermentation, which had not been possible before. This had meant that London beers were highly attenuated, as there was no way of stopping the fermentation until the yeast was ready to do so. This meant that pretty much all the fermentable sugars were consumed by yeast. The attemperated beers could have their fermentations stopped at the brewer's will. The effect of attemperation, therefore, would have been to make the beers sweeter as residual sugars remained.
This was on top of the changes in flavour that would have accompanied the changing malt bill. Estimates suggest that differences in the kilning regimes between pale and brown malts would have seen brown malts yield up around 10% less sugary material – some fermentable, some not – than pale malts. It was this extra 10% that the brewers wanted to exploit, after all.
Attemperation also allowed brewers to reduce maturation times by adding a small amount of stale beer back in to make up for the change in flavours that would result. Attemperators were first adopted by naval breweries in 1791, but did not find favour in the London Porter houses until the start of the 19th century. It is likely therefore that the flavour of Porter towards the end of the eighteenth was changing, as a result of the use of different malts, and greater control over the various processes.
This the brewers attempted to counter by bringing the wheel full circle, and reintroducing blending in the pub cellar once more. This time it was done surreptitiously
“ All the London Porter is professed to be ‘entire butt’, as indeed it was at first, but the system is now altered and it is very generally compounded of two kinds, or rather the same liquor in two different stages, the due admixture of which is palatable though neither is good alone. One is mild and the other stale porter; the former is that which has a slightly bitter flavour from having been lately brewed; the latter has been kept longer. This mixture the publican adapts to the palates of his several customers, and effects the mixture very readily by means of a machine containing small pumps worked by a handle.” xx
This practice of mixing via the beer engine seems to have lasted throughout the nineteenth century, as far as the bigger brewers output were concerned. Smaller brewers carried on with a true ‘entire’.
More significantly the attemperator effectively allowed all year brewing. It was at this point that the technological advantages unique to London vanished and other brewers could use the new technologies to catch up. However, it was not Porter that the country brewers rushed to brew, for around this time there was a profound sea change in the preferences of London drinkers. Suddenly Porter was old hat. By 1819 only 10% of Barclay’s London trade was concerned with old ‘Stale Entire Porter’. The rest was ‘mild’. By 1833 a witness to the Committee on the Sale of Beer was able to remark that:-
“ The London drinker will now have nothing but what is mild, and that has caused a considerable revolution in the trade, so much so that Barclay & Perkins, and other great houses, finding that there is a decrease in the consumption of porter, and an increase in the consumption of ale, have gone into the ale trade; nearly all the new trade is composed of mild ale.” xxi
These mild ales were not the small beer we think of as mild today. They were still quite strong. Admittedly not as strong as old vatted porter. They were harder to adulterate, (adulteration was once again a problem at the start of the nineteenth century as malt prices went up to pay for the wars with Napoleon) and, along with the premium priced Burton Ales, were regarded as more refined. Something that appealed to the growing middle and commuter classes.
The eighteenth century had been the century of Enlightenment and toil that laid the foundations for a new industrial world. Porter was the beer of the that century. It was the food and fuel of the industrial revolution, but when the brave new world was built it was constructed with no place for Porter and the mantle of brewing capital of the world passed from London to Burton-on-Trent.
To read the story of Burton you will need to visit www.india-pale-ale.com