“Originally, the tuns were roused with mechanical power-driven paddles arranged on the floor of the tun, but it was almost impossible to keep these even reasonably clean and they are now being replaced by compressed-air rousers, which consist of a venturi tube in aluminium in the throat of which is arranged a 0.75-in. nozzle. The potential energy of the compressed air is converted to kinetic energy in the venturi, thus inducing movement of the liquor mass. The unit is small and compact and readily removable for cleaning and is arranged on the floor of the tun. The air rouser gives excellent results, promoting vigorous circulation which can be easily controlled by the air valve, the operating pressure of the air being about 15 lb. p.s.i.g.”
Journal of the Institute of Brewing Volume 55, Issue 5, 1949, page 284.
I had to look up what a venturi tube is. Partly to make sure it wasn’t in OCR error. Turns out it’s a tube that gets narrower in the middle of its length. As a liquid passes through the narrow section. Its velocity increases and its fluid pressure falls. Still not totally sure how this makes the wort circulate. One thing I do know: a tube sounds a lot easier to clean than a mechanical paddle.
We now move on to the skimmers. Which are really a sort of cleansing vessel, that is somewhere primarily concerned with yeast removal.
“As the top fermentation process is used, means are provided for the mechanical removal of yeast from the beer surface. This is done in skimmer, of which there are 24 arranged on the three top floors of the fermenting house. The skimmers are large shallow cast-iron vessels each of 425 barrels holding capacity and are 57 ft. 8 in. long by 12 ft. wide and 4 ft. 3.5 in. deep. When the gravity in the fermenting tun has reached the pre-determined figure above primary gravity, the beer is pumped to the overhead skimmers. Yeast is collected by the dropping system, the skimmers being worked in vertical banks of three vessels.”
Journal of the Institute of Brewing Volume 55, Issue 5, 1949, page 284.
I make the total capacity of the skimmers 10,200 barrels. Or around three days’ worth of brews. The dimensions of the skimmers are very different from the fermenters. They were 28 ft. long and 20 ft. deep. The skimmers were less than a quarter of the fermenters depth but more than twice as long.
I’m about confused by mention of the dropping system. That usually meant starting fermentation in a deep cylindrical vessel than dropping to a shallow square one. From the mention of them being used in a vertical bank of three – presumably one on each floor – I assume that they dropped beer from the top skimmer to lower ones.“Of the eight skimmers occupied by a brew, one is a balance vessel fitted with the orthodox parachute or movable yeast hopper. Ordinary skimmers have a yeast trough on the end of the vessel, and the yeast is manually skimmed to the trough and dropped into the yeast collecting vessels below each bank of three skimmers. Each skimmer yeast trough is fitted with two outlet chutes and a portable plug which allows the yeast from the skimmers to be passed down selected chutes to the yeast collecting vessels below. In this way a yeast crop for pitching can be kept isolated.”
Journal of the Institute of Brewing Volume 55, Issue 5, 1949, page 285.
A parachute, in this context, is an inverted cone that floated just beneath the surface of the wort. The ordinary skimmer was just a plank that was moved across the surface of the wort skimming off the top of the yeast head. They’d want to keep the pitching yeast isolated as this would have been collected at very specific times to ensure that it was healthy and suitable for repitching.
As it took eight skimmers to hold, they must be a whole day’s output by “brew”. Eight skimmers could hold 3,400 barrels.
Yeast collecting vessels next. Surely the most exciting part of any brewery.
re: venturi - I think they use them to oxygenate wort inline too: https://youtu.be/cOA4tXvjC5s?t=1m33s
ReplyDeleteThe whole idea of skimmers is fascinating
ReplyDeleteMaybe I'm looking at things from a modern standpoint, but why do they need skimmers? Why aren't they just letting it flocculate and then harvesting.
Yes, yes, "to clarify" the beer. Really, what the heck does that mean. It doesn't make sense to "clarify" when there are still gobs and gobs of yeast in suspension. Like trying to sweep the sand off the beach.
My guess would be that since they were not using conical fermenters, getting the good stuff out of the bottom of a big pit fermenter would be a total pain in the roo. So much easier to just harvest it from the top.
None-the-less, I would expect that it gave a slightly different flavor to the end product. Selectively repitching the yeast that flubs to the top would produce different results from taking the best and the brightest from the bottom of the cone.
So, clearly [see what I did there] there was some benefit and hopefully some science behind this. I'd love to hear what it is.
Anonymous,
ReplyDeleteskimming at the right time is the easiest way to collect healthy yeast. And as they almost collected yeast that way, it had already been selected. Skimming isn't intended to clarify the beer, just collect yeast.