You might think filling up a cask with beer is a simple process. Well, you're wrong.
First of all the beer must be in the right state in the right place; this means it must have finished it's dry hopping period and be ready (or as ready as it's going to be) to be packaged. Easy....
Then, we have the casks. Imagine, if you will, a cask of beer at a pub. It's delivered. gets drunk dry (hopefully) then it's put outside empty for collection. All well and good, except a lot of landlords these days don't bung up (leave a cork and spile in the appropriate holes) the casks.... in winter this isn't a huge issue, but in summer it allows fruit flies to lay their eggs inside which result in small chrysalises of the flies dotted all over the inside of the cask, and they're incredibly hard to shift! Then you have the sun baking the contents dry and then frying onto the inside whatever happens to get inside the cask.... this is generally worse with metal casks although plastics aren't immune to a bit of baking!
Then, it gets picked up and there begins the shit job of making it fit for being filled again!
Once our filthy, fly-encrusted sun-baked cask finally arrives back at the brewery it's inspected by a gagging employee - who wishes he'd not eaten before inspecting dozens of rancid casks - before being steam cleaned at 130c inside and out. This sterilises the cask and removes the majority of the assorted crud, hop bits, yeast, flies and other detritus from the cask rendering it hopefully fit for stage 2.
The next stage involves a manual check of the cask's interior condition - basically by sniffing it when hot (to see if it smells "clean" and not musty or stale) and looking inside with a torch when it's cooled a bit (else you can't see because of steam!). This will ascertain whether the cask is physically clean and free from contamination; if not it goes back through the steam cleaning process and is tested again. In the very few occasions a cask is rejected 3 times (usually in summer when the fruit flies are more common) it's given a week's soak with caustic solution then goes back into the steam cleaning pile to begin the process all over again!
If the cask passes the visual / nose inspection then it's passed to the next cleaning step, a hot date with hot kegbrite! This chemical is sprayballed (via our "mini-whirly" sprayheads!) into the casks at high velocity and hopefully removes any remaining crud and, more importantly, cleans the areas the steam washer doesn't get to properly! After 30 seconds the casks are removed, then rinsed with water. There is no further manual check of the casks as this stage is purely to do a "deep clean" of what is already a clean cask.
The final stage is to rinse the by now immaculate (we hope) casks with peracetic acid solution which renders them "biologically clean" (there's a massive difference between this and physically clean") before being arranged as per this photo. The final stage is the addition of the "finings" (fish guts which make the beer clear) and "priming" (sugar dissolved in water) which, when the beer is transferred from the conditioning tank under CO2 pressure, will mix and give the finished beer clarity and "condition" (sparkle, as the yeast still in the cask will wake up and eat this new easy to digest sugar creating CO2), before - as can be seen here - a flush with CO2 to make sure when the casks are filled no oxygen is inside which stales the beer and diminishes the all-important hop character.
Then the cask can go into cold storage before being sold and transported to a pub, where the whole cycle begins again!