First, a few disclaimers: I'm not an accountant. I'm not a publican. I'm not a cellar technician. I'm not a lawyer. There's a whole heap of things that I'm not.
I illustrated the keg returner the other day, the "legitimate" use of such things is advanced as enabling the recovery of those few pints that would be otherwise lost during line cleaning.
The line that carries the beer from the "cellar" to the tap contains an appreciable amount of beer For 3/8in tube it's something like 30mL per metre, I think. (while we're mixing imperial and SI units, that's about 10mL each foot of 6.3mm ID line. More in the wider stuff traditionally used for cask) There's various devices along the way that also hold a bit (chillers, fob detectors, pumps, etc). Typically, this volume would be lost when line-cleaning is undertaken, i.e. as water or cleaning solutions displace it from the system.
A number of gizmos are on the market which offer to save this wasted beer. Some divert it into a little sealed vessel attached to the system, from which it can be reintroduced into the line after cleaning - of course, that little bottle will need cleaning at some time - but this doesn't seem like an entirely bad idea. Some cleverly disconnect the beer supply (keg) near the end of a session, while allowing you to sell what's already in the line. Some (for cask) allow the line contents to run (slowly) back into the container after the session - although this would leave the line dry, which may not be such a good idea. In other systems, the beer leaves the dispense equipment - into a bucket perhaps, and is manually reintroduced to the container - these are the ones that look distinctly dodgy to me. You'd definitely want to be sure that Customs & Excise / Trading Standards / Environmental Health aren't going to pounce on you.
Even ignoring effects on beer quality - although I suspect that they might be significant - and while we're very much in favour of line-cleaning, there's something troubling about this whole thing: If you have a look at any of the marketing material for these devices, they'll always have a "cost saving" example worked out. They always base this on the selling price of the wasted beer. You waste two pints that you could have sold at £3 each, that's 6 quid income lost, per line, per week! Right? See what an earner this gizmo (and the time spent operating/cleaning it) could be!
As I said, I'm not an accountant, but surely you're not saving any more than the shortage cost (principally restocking cost) of the beer? You'll just buy 2 pints more beer from your supplier. I realise beer that's in the cellar (and hooked up) has to carry some share of the overheads - but not as much as beer that's made it into a glass. Surely?
I know that some tenants have an allowance for line-cleaning effectively built in to their business arrangements. In which case recovering that beer really does generate (not very much) extra income - but only by selling (potentially) damaged goods as new. Which really can't be a good idea. Can it?
News, Nuggets & Longreads 10/10/2015 - This is our pick of the most interesting and/or eye-opening beer- or pub-related reading from the last week. → Neil McDonald of Home Brew Answers suggest...
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