Burton Union
Firestone Union (note the collection buckets in the background)
And what I'll call "PC Union" (Plastic Cap Union):
Due to fridge-geometry I've started to use plastic jerry cans for fermentors, rather than the typical plastic pails or barrels, they are easy to use, but it does make it a harder to see what is going on or to interact with or top crop the yeast.
By drilling a hole in the jerry-cap (slightly smaller than the plastic tubing) and then forcing the plastic tube into the hole it makes an air-tight seal.
The other end of the blow-off tube was put into a 2L glass bottle with 1L of cooled boiled water (with a cling-wrap collar to keep out any bugs).
Filling the 25L jerry with about 23L of wort seems to be the ideal target for the active yeast - at high krasuen - to be forced up the blow-off and to be collected in the bottle.
3 days into fermentation (a Bank's Mild from BYOBRA, hence the dark wort colour) and after high krasuen, the blow-off was removed (and replaced with cling-wrap) and the collection bottle chilled in the fridge over night:
The result is an ideal amount of clean freshly harvested ready to re-pitch or wash-and-store yeast, all with little or no effort and with very minimal risk to sanitation or any related issues.
The same could easily be done with a bucket or barrel fermentor by using a blow-off tube suitable size for the hole in the lid, and then sealing the lid well to prevent any escape of gas, yeast or wort.
Too much head-space means the yeast would not be forced out of the fermentor and too little head-space would most likely make much more of a mess.
When I posted this on the AHB website, I was reminded that for those who use better bottles or glass USA-style fermentors collecting the yeast this way is ever easier. Someone also provided this link a BYO mag Build a Burton Union System: Projects which returns the wort to the fermentor in a true 'union' setup.
