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Porter. It went mild in the second half of the 19th century. Aged, or Keeping, Porter and the vats needed to make it disappeared. But how quickly? It just so happens I've unearthed a few relevant numbers.

Did I mention my Whitbread project? I must have. I'm trying to collect the set of their brewing records. The London Metropolitan Archives has every year from 1805 to 1975. I've only about 10 years missing for the Porter ones, mostly post-WW II. So I'm getting a unique insight into how Porter brewing mutated. Including the move away from aged Porter.

Let's quickly run through the development of Porter. Early Porters were the first beers (and they were Beers, not Ales) that London brewers had aged themselves. Before publicans or third parties had bought mild malt liquors and aged them in their own cellars. Spotting the public's liking for a bit of age, some brewers began ageing their Brown Beer. Not for immensely long periods, just six months or so. Enough to acquire the desired flavour. And Porter was born.

Initially, all Porter was aged. Until someone noticed that you could get the same aged effect by mixing a small quantity of beer that had been aged 12 months or more with fresh mild Porter. Two distinct types of Porter were brewed: Running Porter and Keeping Porter. What was the difference? Well, apart from being aged in enormous vats, Keeping Porter contained more hops. But the grists and gravity were identical.

In the 1840's, 25-30% of the Porter Whitbread brewed was K, or Keeping Porter. Which tallies pretty well with the recommendation of brewing manuals to mix around a third aged beer with fresh beer. As you'll see in the table below, there was a slight downward trend in the 1850's, and occasional years where far less Keeoping Porter was brewed, less than 10% or total Porter output.

The decline of Whitbread's Keeping Porter
Year
no. brews K
brewsize K
K total barrels
% K
KK
% KK
Total running Porter
% running Porter
total all Porter
1840
42
803.6667
33,754
21.78%




121,244
78.22%
154,998
1845
56
809.0179
45,305
30.09%




105,284
69.91%
150,589
1847
45
















1848
58
















1849
54
800
43,200
29.04%




105,567
70.96%
148,767
1850
48
817.0833
39,220
28.25%




88,562
63.80%
138,819
1851
53
781.7925
41,435
30.00%




91,312
66.11%
138,114
1853
44
789.9773
34,759
22.41%




106,323
68.54%
155,125
1854
43
780
33,540












1855
13
862
11,206
8.54%




85,239
64.99%
131,160
1856
29
811.6897
23,539
18.36%




104,693
81.64%
128,232
1857
30
827.9
24,837
18.80%




107,296
81.20%
132,133
1858
38
803.5263
30,534
20.14%
7,002
4.62%
100,924
66.56%
151,618
1859
13
759.3077
9,871
5.97%




119,794
72.48%
165,284
1860
22
719
15,818
9.04%




108,681
62.13%
174,929
1861
11
757.0909
8,328
6.89%
7,767
6.43%
104,691
86.67%
120,786
1862
29
770
22,330


1,400








1863
15
796.5333
11,948
7.42%




118,552
73.64%
160,993
1864
32
815.0625
26,082
18.70%
800
0.57%
102,198
73.27%
139,472
1865
21
813.9048
17,092
10.83%




111,381
70.58%
157,810
1866
7
782.5714
5,478
4.11%
1,666
1.25%
126,037
94.64%
133,181
1867
3
755
2,265
1.64%
745
0.54%
118,923
86.15%
138,047
1868
6
752.1667
4,513
3.61%




120,439
96.39%
124,952
1869
4
723.75
2,895
2.43%




116,348
97.57%
119,243
1870
4
796
3,184
2.74%




112,868
97.26%
116,052
1871
0


0
0.00%




103,543
100.00%
103,543
Source:
Whitbread brewing records held at the London Metropolitan Archives


Notes:
1839, 1854 and 1862 quantities estimated from the number of brews


In the middle of the 1860's, there was a sudden and dramatic collapse in Whitbread's production of Keeping Porter, dropping from 17,000 barrels in 1865 to 5,500 in 1866. For the remaining years of the decade, there were a handful of brews. Until 1870, when the final four brews occurred and Whitbread's K disappeared forever.

How did Keeping Porter disappear? Remarkably quickly


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