Bear in mind that this was written in 1870, just as artificial refrigeration was becoming a commercial reality.
"The Quarterly review, Volume 131" 1870, page 401.
Temperature control of wort during fermentation was one of the big technological advances of the late 18th century. It allowed London brewers not only to brew 12 months of the year, but to produce a much more consistent and stable product. Why am I repeating this? Because I still get people telling me that summer brewing wasn't possible until the 1870's after the introduction of artificial refrigeration.
"There are many varieties of management while fermentation is going on, as well as after its completion — a period which depends on temperature, goodness of yeast, strength of 'gyle,' weather, and other circumstances. There are yet other variations in the manner in which the beer itself is managed. Some is vatted for weeks or months, some is sent out in the casks in which the fermentation has been completed. Bitter beer generally has a certain quantity of fresh hops put into each cask. These act as finings and improve the flavour."Now we learn something about the different conditioning practices of the period. Vatting, cask-conditiong and dry-hopping. Ironically, 1870 is just about exactly when vatted Porter disappeared. Most other vatted beers would soon follow.
"The Quarterly review, Volume 131" 1870, pages 401-402.
Perhaps there is no more remarkable example of a rapid increase in demand produced by improvement in manufacture than the increase which has taken place in the demand for bitter beer. Forty years ago bitter beer was hardly known, its manufacture being almost if not wholly limited to one firm in London, and its consumption being confined to India. Now, in the town of Burton alone there are not less than twelve breweries of bitter beer, two of which are among the largest in the world, one of these two being, we believe, the very largest establishment to be found anywhere. The consumption of malt at Burton now amounts to something like half-a-million quarters per annum."
"The Quarterly review, Volume 131" 1870, page 402.
And finally something about specific types of beer. Porter seems to have fulfilled the role later taken on by Mild - as a dumping ground for slops and anything else a publican might want to throw in. I wonder if Mild may have been better off remaining pale in colour?
The story of the rapid growth of Pale Ale in the middle decades has been told many times. Many have interpreted this as meaning Pale Ale became the biggest-selling type of beer. Which just isn't true. The true winner in popularity in the period 1830 to 1870 was Mild Ale, supplanting Porter in the affections of drinkers. Pale Ale remained an expensive niche product for all of the 19th century.
Half a million quarters of malt would produce around 2 million barrels of beer. But remember that Burton brewers brewed much more than just Pale Ale.