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We're back in the old-ish Aitken's brewery. Though as you read the passage below you'll realise that it had already been greatly altered and enlarged.

The original brewery was all on the south side of Newmarket street. But during the 19th century a new, much larger set of buildings had been added on the north side. These wren't concerned with brewing, boiling or fermenting, but were ancillary buildings such as stores.

"Retracing our steps, we came to the mashing-stage, 40 feet square, situated in the centre of the brewhouse. Here we were shown two mashtuns, constructed entirely of copper, and commanded by a Steel's mashing machine. They both contain gun-metal draining-plates, and each is capable of mashing twenty quarters of malt. The underbacks are below the tuns, from which the wort is pumped up direct to the coppers. We have previously written so much on the nature and object of the mashing vessels used in the breweries, that, on the present occasion, our attention will be more particularly directed to the next and following processes."
"The Noted Breweries of Great Britain and Ireland, vol. 2" by Alfred Barnard, 1889, page 194.
That's what I've been waiting for: the capacity of the mash tuns. At 4 barrels a quarter, that's 80 barrels a brew per mashtun. Assuming one brew in each per day and 300 brew days a year, that comes to 48,000 barrels annually. Not enormous by English standards, but a reasonably-sized regional brewer in Scotland. Thanks for not bothering to describe them in any more detail, Alfred. At least there's an illustration.

Looking at the way that bloke is standing in the mash tun, it doesn’t look like it has internal rakes. Which tells me something. What? That they almost certainly didn’t perform underlet mashing like London brewers. About an hour into the mash more hot water is added to the mash from below (via the underlet, hence the name) to increase the temperature of the bed. It’s a simple form of step mashing. Whitbread were still mashing this way at Chiswell Street in the 1970’s.

Underlet mashing is one of the reasons many London brewers retained internal rakes even after installing a Steel’s masher. Because the practice was to have the rakes revolve once or twice after the underlet to mix the hot water added thoroughly with the grain.
"After this we made our way to the cooling department, covering the top storeys of the adjoining building, and overlooking the main thoroughfare. One of the most striking objects it contains is the hop-back, a large vessel with a graduated bottom, constructed entirely of copper, and containing across its breadth, at the far end, two rows of copper draining-plates. This vessel is used as a combined hop-back and open cooler, and is unlike any we have seen before.

In the same apartment there are two Morton's refrigerators, cooling at the rate of thirty barrels per hour each, where the ale wort is further cooled over the mazy lines of innumerable cold-water pipes before passing into the great copper mains, which convey it to the fermenting rooms."
"The Noted Breweries of Great Britain and Ireland, vol. 2" by Alfred Barnard, 1889, page 194.
I wouldn't have minded an illustration of that cooler/hop back device. I can't quite get an image of it in my head. We all know what a Morton's refrigerator is, don't we? No? OK then. It's a bed of horizontal copper pipes through which chilled water flows. Wort flows over the pipes and is cooled.

"Our progress was now downwards, and after inspecting the furnace fires, or copper hearths, as they are called, we made our way back to the courtyard.

Passing beneath the archway, immediately within, on the left-hand side, appears the magnificent tun-room, re-built in the year 1866 and again considerably altered and enlarged in 1878. The building is of solid construction, and is lighted by nine windows in the roof, which contains improved patent ventilators, is ceiled with pitch-pine, and is supported by immense iron columns All the vessels are elevated on brick piers, and fronted by a gallery, which adds much to the impressive effect. The illustration, which heads this chapter, is taken from a photograph, and shows a section of the interior of this tun-room. There are fifteen vessels in this department, all constructed of polished pine, nine of them are fermenting squares, and the other six settling backs, and each is fitted with an attemperator. The copper mains, by which they are filled, are in short lengths and detachable, so as to be easily cleaned. At one corner of the room there is a small Otto gas engine, used for pumping the beer from the tuns into the backs. From this side of the brewery the beer is conveyed through great copper mains, laid under the street, to the racking-rooms on the north side of the brewery. Before leaving this place, we paid a visit to the engine-room, situated under the mashing-stage, and containing an engine of fifteen horse-power, and a large steam boiler. Here also are two sets of pumps for the coolers and refrigerators, reversible, in case of breakdown, and the two great metal underbacks, each fitted with duplicate stopcocks. Walking through this apartment we came to a paved chamber where the spent hops are pressed. The machine is worked by hydraulic pressure, and the wort expressed from the hops is pumped up again to the refrigerators, from which it passes to the fermenting vessels.
"The Noted Breweries of Great Britain and Ireland, vol. 2" by Alfred Barnard, 1889, pages 194-195.
It's clear that Aitken's brewery had been increasing its size and updating its equipment frequently in the second half of the 19th century. Boom days for Scottish brewing.

I'm not 100% sure what is meant by "nine of them are fermenting squares, and the other six settling backs". Fermenting squares I understand. You can see them in the illustration. Settling backs sound to me like part of a dropping system. It's a shame there's not more description of how these two types of vessel were used.

Fullers had fermenting rounds from which fermenting wort was dropped into settling squares. The way Fullers system of fermentation worked, the beer was only in the rounds 24 hours and several days in the squares. I can't see that working with the setup at Aitken, where there were fewer settling backs than fermenting squares. My guess would (and this is only a guess) that the beer was transferred to the settling backs when fermentation was pretty well complete. That would tally with the description of beer sometimes being put into squares in Edinburgh breweries, mostly to cool it down.

Those fermenting squares look pretty large to me. Look at the height of the things. I reckon they must be 12 feet square and the wort at least six feet deep. A quick calculation (an imperial gallon is 277.42 cubic inches) gives me a figure of about 150 barrels. That's much bigger than the piddling 40 or 50 barrel ones they had at William Younger. Which might explain why they need the settling backs. A larger volume of fermenting wort generates more heat.

Pressing spent hops to squeeze out the last drops of wort was becoming commonplace in large industrial breweries. I'm sure it still goes on today. But what about the quality of the wort extracted? Wouldn't it tend to be full of crap from the hops?

There will be at least more more instalment on the old Aitken brewery. Then we can move on to the recollections of former Aitken employees.