Recently, I was judging at a pro-brewers' competition and while there were some stunning entries, an obvious pattern emerged. The winning entries fell into two categories - they were made shortly before the competition started or they were made by breweries that performed regular QC testing. The latter breweries won big.
By and large, small breweries without QC testing don't get to sample their product outside of their own brewery. It might travel down the street and stay on tap for a week or so, but it's generally sold where it's made. It's usually pretty good. Though every brewer knows that fresher is better, most of them aren't aware of just how truly awful beer can become if it's poorly packaged. And unfortunately, there are only two types of packaging: perfect and everything else.
Perfect packaging eliminates oxygen ingress and stabilises the product against changes for as long as possible. In most of Europe, it must have a shelf life (at room temperature) of at least 6 months. It has a date and/or batch stamp and the brewer knows exactly when to expect the product to be pulled.
Everything else is missing one or more of these criteria. I will avoid ranting about breweries that can't bear to hear that their product is nothing more than home brew on a big system, but suffice to say that the "cranky old woman" part of me still stands.
Now don't get me wrong, (or CAMRA will take away my membership), but "live" or bottle conditioned beer still has a place - as long as both brewers and consumers are aware that the product is expected to change (or be inconsistent) and travelling is not recommended. Neither are temperature changes, humidity level changes or having a bad attitude somewhere in it's vicinity. A date and/or batch stamp is also advised.
It should also be noted that just because your mobile canning line says that there is 0% oxygen after packaging, doesn't mean it's the whole story. By and large these samples are tested a day after canning, at which point they will be correct - there will be 0% dissolved oxygen. That's because all the oxygen has already reacted with everything it can and the damage has been done. The product will continue to deteriorate and the poor brewer will be left wondering why their product is hot garbage after a month on the shelf.
So lets take Weihenstephaner as our example to emulate. Their hefeweissen is generally considered a style exemplar. It's bottle conditioned, as all good hefeweissens should be, and yet seems to remain consistent for months when craft examples fall to pieces after only a few weeks. The secret is pasturisation, which is easily doable at the homebrew level.
In a bottle conditioned beer, yeast will consume the small amount of oxygen left during priming. At pasturisation, you inactivate the yeast, as well as greatly slow down protein and lipid degradation.
Now, before I let you go away thinking that pasturisation is all rainbows and sunshine, it's not. Pasturisation will not fix shoddy bottling practices, excess oxygen, lack of sanitation or poor fitting caps/lids. It will also slightly reduce volatiles (aka esters).
So on with the actual instruction.
Pasturising comes in two forms: flash and tunnel. Flash pasturisation is largely used for kegs and essentially runs through the opposite of a chill plate. As a home brewer, you can use a chill plate (though I'd sterilize it first) and submerge it in some appropriately temperatured water. We'll get to the specifics in a moment.
Tunnel pasturisation is what you use when it's already packaged. If you're bottle conditioning, make sure it's finished carbonating first and that those caps are on tight. You're going to heat the entire package so that the liquid hits between 60-72C.
What you want for industry standard is 14-15 PU or pasturising units - that is, a liquid held at 60C for 60 seconds. I won't get into the math, but this means you can hold it at 60C for 15 minutes, or 72C for 30 seconds. Higher temperatures will reduce volatiles more and holding it at 60C longer than 15 minutes will start to age it prematurely, so keep that tucked away when you decide how you're going to do this.
The first step is to figure out how long it's going to take to warm up your beer from bottling temperature to pasturising temperature. At my latitude, I've found that 82C in a 6 gallon pot will bring the liquid in 6 cans up to 72C in 30 seconds and bottles in 50 seconds. You'll have to sacrifice some beer to figure out the best temperatures for your setup.