Wednesday, August 15, 2012

Triple Brewing and How To Go Forth and Multiply

Something we've been doing for quite few years now is triple brewing - not brewing tripel, the Belgian strong blond ale as in Westmalle Tripel or Chimay White - but simply doing three brews consecutively into one fermenting vessel. If one's brewlength (the amount of each brew, i.e., 30 barrels) and FV capacity are the same then there is no need for such extravagant behaviour, however if one has a FV thrice as large as the brewlength, then doing three brews consecutively into said FV will work effectively. The brews can go in three days in a row, which what we do currently with Bigger Bertha (its other name being CT7)  shown below, or straight after each other, without a break, if one is shift brewing around the clock. The first at 8am, the second at 3pm and the third at 10 pm.
Our regular brewlength is 30 bbls (barrels) or in metric speak, 50hl (hectolitres or 100 ltres). We have 4 sizes of FVs - 20, 30, 60 & 120 bbls which means most of our brewing is in 30 bbl aliquots. The two smaller 20 bbl FVs get  brews of 20 bbls and the 30 bbl FVs get the standard 30 bbl brewlengths. But for the two larger FVs (FV8 at 60 bbl and CT7 at 120 bbl, the latter revelling in its status as a dual-purpose vessel - fermenting and conditioning) the dark arts of double and triple brewing must be practised. Those of you with a mathematical bent will be asking yourselves why we don't do quadruple brewing into the largest tank being of four times our standard brewlength of 30 bbls. The answer is we need some freeboard or space above the fermenting wort for the yeast head to rise up. And indeed it does. Especially with the stronger beers. For Blackfriar, our 7% Scotch Ale, for example, we'll brew 3 x 20bbl brews into FV8 and it likes to foam up with serious intent. 
I was reminded of this today by our summer placement student from Heriot-Watt University, Liam, who asked how much yeast we pitch into a double or triple brew. A good question. We pitch 10 litres of yeast slurry to give 18 million cells per ml of wort for the first brew of 30 bbls which is oxygenated for 30 minutes. As the cells take up the nutrients and the oxygen present in the wort, the yeast cells multiply sufficiently to be able to cope with the next brew coming in. This second brew only gets 10 minutes of oxygenation, which allows the now-multiplied yeast to grow even more to be able to ferment the doubled brew in the FV and also, after the third brew is added without any oxygen, to continue the fermentation to completion. A simple tale of yeast going forth into the fermenter and multiplying.
Lia Fail yeast head getting going in style
It's important to get enough yeast cells to ferment out the wort but we don't want too many otherwise the beer will have the wrong flavour, and beer is all about flavour. Having the yeast multiply, generally fourfold during a fermentation, is good for our flavour characteristics, and it's also a lot easier and simple to pitch 15 litres into a brew than 60 litres. 
As far as yeast vessels are concerned, we use simple 25 ltr drums into which yeast is run, merely by opening the valve and letting the yeast slurry flow in gently, from the bottom of the cone of an FV of one of the previous week's fermentations.
The drums are stored in a fridge at 3 degrees C where they sit until needed for brewing over the following 6 days. I wouldn't really want to leave the yeast in the fridge longer than a week as it will begin to lose viability and vitality quite rapidly after then. Pitching involves the yeast being pumped into the FV in-line with the oxygenated wort using our yellow peristaltic pump shown below. 
This pump from the peristaltic experts, Watson-Marlow, works like a hand milking a cow, gently squeezing the milk down a teat into the milk-bucket, by gently squeezing the yeast through a flexible hose (the clear hose coming out of the right-hand side of the pump) into the fast-flowing wort coming from the heat-exchanger and thus into the FV, getting good mixing with the wort in the process. 
Our pitching set above, where wort travels along the green hose and the pale beige yeast slurry is coming in from the left. We find this method of pitching gives consistent results in fermentation and flavour and it certainly beats opening up a fermenter lid and pouring in 15 litres of slurry and helps avoid infections from wild yeasts and bacteria which will do no good for the taste of the beer. And what we're all about is, of course, the taste of the beer! Like in this pint of Thrappledouser...
Slàinte! Ken