One part of the chemical engineering where we almost seemed to enter the realm of science fiction was with phase diagrams. At certain pressure and temperature combinations the liquid and gas phases of a substance will no longer be distinct, instead being a supercritcal fluid. See, I told you it was almost science fiction.
Now it may not be the sort of pressues and temperatures you'll find in a brew house but using supercritical CO2 is one way of making hop extracts. And I'd never seen it being done, until my trip to Germany.
The reason for my trip to Bavaria was to visit a hop company, and I got to have a tour of where they make the hop extracts and hop pellets. The extracts plant was first, starting with ethanol extract. In the tank pictured the ethanol extraction took place, with the ethanol percolated through the hops. I innocently asked if they fractionated the extract at all...
|This is at ambient pressure so we've not got supercrital yet|
...before being shown the biggest rectifier I've ever seen:
Next we came to this large tank. I think this was a CO2 tank as we were heading to that end of things.
When it comes to engineering I like to see things on a proper industrial scale, and there was no pretence of craft here. The CO2 was at a pressure of 290 bar, so the vessels were impressively thick to cope with it:
If I've understood it right mere liquid CO2 is a non-polar solvent, but supercritial CO2 becomes polarised and its dissolving power increases. There is little flavour difference between the different types of extract, but there is some variation in the composition of the extracts, for example ethanol extracts contain more hard resins than CO2 extracts.
After the extract plant we got to see where hop pellets are made.
|Bales of hops being broken up|
|Nascent hop pellets|
There are a range of dies for the pellets. The thicker the die the harder the pellet becomes. Different ones have to be used as higher alpha acid content in the hops also makes the pellets harder.
|Can't remember what this was. Probably contained hops though.|
|Vacuum packing the pellets|