As the London Porter brewers grew, and as their expertise developed, there was a further significant change in Porter manufacture. Price stability was, in part, maintained by the fact that yield per bushel rose steadily throughout the century. Not all of this was due to better equipment, vatting, or improved brewing techniques. A major influence was the fact that Porter brewers turned their backs on the high-dried brown malt that had created the beer in the first place.
Even as early as the late 1730’s various authors were stressing the importance of applying ‘scientific’ principles to brewing – even if some of the ‘science was fairly. Medieval. Temperature, for example - crucial to both malting and mashing – was gauged in such scientific terms as ‘just tolerably hot’, - reminiscent of Trial by Ordeal - or ‘ones’ reflection just visible through the steam.’ This was unsurprising since science is impossible without measurement, and the only things that could be measured were weight and volume.
Proper
scientific investigation had to wait for two important inventions;
the thermometer and the hydrometer (which measures the density of a
liquid compared to water).
The thermometer appeared in the 1750s. It allowed more precise control
and consequent efficiencies.
“ The thermometer, by shewing the different degrees of heat of each part of the year, informs us, at the same time, how necessary it is the proportions of boiling water to cold should be varied to effect an uniform intent; also that the heat of the extracts of small beer should differ proportionally as the heats of the seasons do: it assists us to fix the quantity of hops necessary to be used at different times; how much yeast is requisite, in each term of the year, to carry a due fermentation; and what variation is to be made in the length of time that worts ought to boil.” xvii
The hydrometer appeared around 1770 but both took time to establish their worth in an industry that was happy to innovate in terms of scale, but strangely reluctant to innovate in terms of practice. Samuel Whitbread saw no point in using one, and they were not in widespread use until after 1784.
The impact of the hydrometer was not principally on brewing practice, but was financial. Only when its financial impact was understood was it universally adopted, for essentially the hydrometer was an instrument of costing.
What the hydrometer allowed brewers to do was to accurately measure the value of malt. Before the hydrometer the big secrets in a brewery were the various mash temperatures (approximate) and the lengths got. After the hydrometer the big secret was the choice of malt and the price paid for it.
The two instruments together (you cannot use a hydrometer without a thermometer) allowed detailed statistical analysis. From 1785 there were published tables of the comparative performance of various malts. The relative inferiority of brown malt became all too apparent. From 1785 therefore brewers started to move away from all brown malt brews to beers made with pale malts and added colourants. These colourants could either be made from sugar, or when sugar use became illegal, ‘patent’ malt was used.
“ If I am correctly informed, there are brewers who draw their lengths for Porter from pale malt, instead of pale and brown, or pale, amber and brown mixed, because the former yields more extract per quarter, and such persons are said to impart the necessary colour by a suitable portion of patent malt – as it is termed - which is a malt roasted to a state of blackness.” xviii
It was the use of patent malts that changed the colour of Porters and Stouts from a rich deep brown to the ‘Guinness’ black we think of today.
Use of the hydrometer had other consequences, too. Firstly, it knocked Hertfordshire malts off their previously held top spot and instead Norfolk barleys began to be seen as premium. Naturally the shift in emphasis from local malting skill to the properties of barley varieties and growing areas had profound agricultural consequences too, which we cannot explore here. Secondly, brewers had no monopoly over the hydrometer. Customs Officers could use them too, giving the government greater control of taxation.
Not only did the hydrometer allow brewers to select the most cost effective malts, it also allowed them to plan ahead. The effects of changes in malt prices could be calculated and responses in alterations to strength, or mixtures of malts could be prepared. The combination of thermometer and hydrometer made an immense contribution to the profits of the brewers, that tends to be overshadowed by more dramatic innovations such as the introduction of steam.
Porter became
a beer brewed from a variable grist malt. Some brewers opted for a
50:50 blend of brown and pale malts, others for an equal blend of pale,
amber and brown. Colour adjustment was obtained by the use of patent
malts in one direction, by dilution with ale in the other.
The first and one of the most important points of attention in the brewing of porter, is the judicious and necessary blending of malt, dried of different shades in colour, or the selection of malt dried to an exactly correct shade.” xix