Saturday, 8 November 2008

The three systems of fermentation 1880-1914

More laugh a minute stuff from "Principles & Practice of Brewing" by Walter J. Sykes & Arthur R. Ling, published in 1907. I wonder if I still have any readers left?

It's not surprising that the more labour-intensive methods described below have disappeared. Even the most sophisticated method of cleansing, Burton unions, is pretty fiddly.

The cleansing system
Probably having its origins in domestic brewing, this was the oldest method of fermentation. Originally, trade casks, that is the casks in which the beer was sent out to customers, were used for cleansing. After about 48 hours in the fermenting tun, the process of separating out the yeast began and the wort was transferred to trade casks. A few breweries still used this old-fashioned method in the early 20th century.

By the late 1800's, it was more usual to use large casks - butts, puncheons or pontos, each holding several barrels - for cleansing. These were known as "loose pieces" because, unlike the more sophisticated Burton Union method of cleansing, the barrels were not permanently fixed to a frame, but could be removed for cleaning. Yeast was pitched at 56º to 60º F and after 36 to 40 hours, when the temperature had risen to about 70º F and the gravity reduced by half, the wort was transferred to the cleansing casks. Splitting the wort into smaller volumes helped to keep down the temperature. If the temperature in the fermenting room was 45º to 50º F, the wort in the casks could get no warmer than 70º F.

In the summer, it was possible that the wort could become too hot so, as a precaution, it was moved to the cleansing casks earlier in the fermentaion, when it was cooler. Burton Unions were fitted with attemperators, so this was not necessary.

Some beer was expelled along with the yeast and it was important to top up the cleansing casks with clear wort. If they were not keep totally full, yeast would fall back into the beer and defeat the object of the operation. In some arrangements, such as Burton unions, topping up occurred automatically. In other cases, it was performed by hand, usually at intervals of around 3 hours.

As far as I am aware, the unions at Marston in Burton are the only remaining example of this form of fermentation.

The skimming system
This began exactly the same as the cleansing method. When the skimming point was reached, the wort was left in the fermenting tun but thoroughly roused. The yeast head was skimmed off every 6 hours. Temperature was controlled by means of attemperators. These were switched on when the temperature of the wort had reached 59º F and so regulated as to allow the wort to rise 1º F every 6 hours. The flow of water through the attemperators was increased when the wort hit 65º or 66º F to stop the wort warming any more. When the fermentation was nearly finished, the the water flow in the attemperators was increased even more to cool the wort down to 60º F.

Skimming stopped when it was estimated there was just enough yeast left to throw up one more head. This was checked by moving aside the head to look at the wort. If it was black and clear, it was ready and no more skimming was needed. If it was brown and opaque, it still contained too much yeast.

The dropping system
This was a variation on the skimming system developed by William Garton. When the wort had almost reached the skimming point, it was let down from the fermenting tun to a shallow settling square. The process of "dropping" both aerated and roused the wort. Much of the sediment was left behind in the fermenting tun.

Once in the settling square, the wort was skimmed and its temperature controlled by attemperators as in the skimming system.

Fullers were using the dropping system in 1910. They usually dropped the wort after just 12 to 18 hours in the fermenting tun. This is the record of a typical fermentation:

The temperatures match pretty much exactly those given by Sykes and Ling in their description of the skimming system.

Most London breweries employed either the cleansing system or skimming system. I am unaware of any brewery that still uses the cleansing system. There is at least one brewery (Refresh for the Brakspears beers) that continues to use the dropping system.

The stone square system
This method, as its alternate name "Yorkshire square" implies, was common in the north of England. It produced beers that were full-bodied and with a high CO2 content. A special type of slow-acting yeast, which needed a great deal of rousing, was used.

A small amount of yeast, just 1 to 1.5 pounds per barrel, was pitched at a temperature of 58º to 59º F. The yeast was mixed with a little wort in the upper chamber, thoroughly roused and then let down into the main chamber through the "organ pipe". The wort was then left undisturbed for 36 hours during which time the temperature rose to 62º F. For the next 12 hours, the wort was roused every two hours. Yeast rose through the central manhole and settled in the upper chamber.

The next stage was pumping. Wort was pumped into the upper chamber and mixed with the yeast that had settled there. The valve in the organ pipe was then opened to allow the wort and yeast mixture to run back into the main chamber. This process was repeated every two hours, starting with 15 strokes of the pump. On each subsequent repetition, the number of strokes was increased by 10. The wort was kept cool by the attemperating "jacket" formed bt the double walls of the square. Pumping ceased when the wort was within 1 or 1.5º of its finishing gravity.

After pumping was over, the yeast which rose into the upper chamber was removed any four hours. Any beer which had risen with the yeast was let back down into the main chamber through the "organ pipe". When all the yeast had been removed, the temperature of the beer was gradually reduced to 60º F. The manhole was then closed and the beer left to settle for 48 hours before being racked.

Yorkshire squares are the only one of the three fermentation systems still in widespread use. Breweries using them include Sam Smith's and Tetley's.


Zak Avery said...

Well, I'm still reading.

Can you clarify what the "rouser" is, Ron - you seem to imply a paddle, and that pumping over is different from rousing, although according to another source, they seem to be the same thing?

Ron Pattinson said...

A simple paddle was used for rousing wort in a normal fermenter. In a Yorkshire square, I'm sure it meas pumping the wort into the upper chamber.