When we’re done boiling wort in the brew kettle, we have to get it to the fermenter. This is called ‘knockout’ and it has to happen at the proper temperature. If it doesn’t, we could shock or even kill our yeast. We knock out ales at sixty-eight to seventy-two degrees, and lagers around fifty.
Wort is the sweet liquid that turns into beer when fermented by yeasts. It becomes sweet by extracting fermentable sugars in the mash.
This is how we get it done. The heat exchanger is a series of stainless steel plates and rubber gaskets pressed close together like a rock-hard, eighty-one-layer peanut butter and jelly sandwich in a vise. The plates form two labyrinthine passageways, one for cold water and one for hot wort. Cold water runs in one way and out the other way; hot wort runs in the other way and out one way. As they pass each other against the plates, the wort cools down and the water warms up. Hence, heat exchanger. Got it?
We dial in the knockout temperature by speeding up or slowing down the flow of cold water with a simple ball valve. We can also speed up or slow down the flow rate of hot wort by controlling the speed of the pump that pushes it from the kettle.
When we’re done with a brew, we run caustic detergent through the heat exchanger, then acid, then pack it with an acid-based sanitizer so it never has a chance to dry out or become infected. Every once in awhile, we run the cleaning cycles in the opposite direction for good measure. We take such great care because if we ever had a problem with our heat exchanger, taking it apart and putting it back together would be a Humpty-Dumpty-and-a-half of a task and could delay our production schedule. Knock on wood for us, would you?
Since we opened shop, we’ve learned a few things about our chilling process. First and foremost, knocking out took a long, long time in the summer--sometimes up to two hours or more for what takes us half an hour to forty-five minutes in the winter, simply because the ground water we ran to the heat exchanger was so warm. We couldn’t even think of doing a lager then. Since then, we’ve installed a pre-chiller that cools the ground water to a reliable, plenty-cold temperature. The pre-chiller is also a plate heat exchanger, but on a much smaller scale. We run chilled glycol, a refrigerant, against the water to cool it down. It’s part of the same loop that cools our fermenters and brite tanks.
If you’re the kind of guy or gal who gets sad at the plight of pandas and such, you’ll be happy to know that the hot water that comes out of our heat exchanger is directed to our hot liquor tank and ends up in the next batch of beer. How’s that for bamboozled?
Bippidy bop. See you next time.
This is the first installment in my regular Sob Stories series, ‘What’s That Thing Over There?” Check back often for more opportunities to pull back the curtain at the extraordinary and mundane of brewery miscellania. And stop asking our poor bartenders what that damn thing over there is.