Thursday, 2 June 2016

The oxygen conundrum bottles versus cans

Cans keep out oxygen, so they say. Bottle tops don't do quite such a good job, so we are told. It's all to do with the seal that can be achieved. Oxygen can sneak through the tiny molecular gap that might be present between glass and the plastic seal on a cap. Metal to metal is a far tighter closure, apparently.

That is all well and good, but is it possible to get beer into the can reliably without oxygen pick-up? As it happens, Stonch has already cast doubt on that. I can't really be sure, except for the fact that the canning lines I have seen seem to not have all that a reliable way of purging with CO2 and there is certainly no pre-evacuation of the can.

However, our bottling line at Hardknott is the double pre-evac counter pressure filling type machine. What this means is that a contraption attaches to the bottle neck sealing hermetically from the atmosphere. Most of the air1 is pumped out. The bottle is then filled with CO2 at a pressure of 1 atmosphere gauge pressure2, i.e. 2 atmospheres absolute. This process is then repeated again, hence the word "double" in the name.

Only then is the beer allowed to flow into the bottle, under a counter pressure of more CO2 at around 2 bar. When the beer goes into the bottle it is extremely oxygen free. When the pressure is released the beer fobs a little, and we set the rate of bottling to get the right fobbing, along with a little squirt of sterile water to help it foam. This fob is all beer and CO2 with only a tiny area exposed to the air.

The canning lines I have seen try to puff out the air with a little tube that goes to the bottom of the can. The beer is filled from the bottom of the can to try and push the CO2/air mixture of unknown purity out of the can. Any fob will have quite a significant area in contact with the air.

In my view to can reliably with low levels of oxygen it would be necessary to do the process in a blanket of CO2, rather than the open systems I've seen.

Cans might keep out oxygen, but I'm fairly sure it is a lot harder to stop it being in there in the first place. The filling process is certainly not as hermetic as with our bottling line.

Because it is difficult to explain in words I did a little animation for our bottling line.

from Hardknott Brewery on Vimeo.

Incidentally, I hadn't really thought about the problems of canning compared to bottling until Jon from Stringers pointed it out to me the other day. All the result of a chat over a beer. Isn't beer good.


1Our vacuum pump gets down to about 0.1 atmosphere absolute pressure.

2Gauge pressure is the pressure relative to the atmosphere.


Ed said...

I wonder if a lot of this stuff about oxygen ingress has been imported from the states. Certainly screw off crown caps, which are popular there, are a lot worse for letting oxygen in than caps you need a bottle opener to remove.

StringersBeer said...

Here's Rob Lovatt (Thornbridge) on the perils of Oxygen pickup in canning.

StringersBeer said...

P.S. I should say that I've never had a beer from a can make me think "Oh, this is oxidised". So I guess the canners are doing a good job. And Thornbridge are famously obsessive-compulsive about Oxygen.

Dave Bailey said...

Well, I've heard some horror stories about canning, especially when mobile canning units are used.

However, I also know that canned beers are generally good. Mostly done by breweries that have invested in equipment and the know-how. Also, the best beer is moved to the consumer as soon as possible. With the exception of stronger and darker beers most beer is best fresh. I know this goes against arguments I've made previously, but my experience shows that beers that are sub 7% are better sold quickly. Although being oxygen free will help shelf life, it is not a panacea. Moving beer quickly is good. The breweries that are doing OK with large scale canning are shifting a shit-load of beer.

Are bottles better than cans? Or are cans better than bottles? I think each have their merits and problems.

I think beer packaged in the brewery where it is brewed is much more of a strong benefit. Packaged on a machine that is cared for by the brewer, and one that has a strong in-house engineering facility. A facility where maintenance is top-notch. Where the beer doesn't move more than a few meters and where it is moved it is kept cold, light free and oxygen free.

If the packaging is done on a machine that is cared for in the brewery, installed correctly, and sanitised well, and not moved around in a truck, the beer is bound to be better.

Much micro-brewed beer in the country is packaged by contractors. The beer is moved in tanks with dubious light protection, no positive pressure co2 blanket and no temperature control. I cannot believe this makes for good packaged beer.

Having said that, I like those nice bag-in-boxes that some of the more caring brewers use. No head space, light tight and moved to the machine the day of packaging. I'll accept that way is OK...

Jez | Brixton Brewery said...

Tend to agree about small canning lines and based on recent sensory analysis(my mouth) I've found beers I've had on draft to be less flavourful in can. Could be down to lots of factors of course but in my mind there's a trend. We recently invested in a counterpressure bottle filler(Meheen) as it fitted our budget, space constraints and more importantly felt it would do a better job than similarly priced/size canning line. It does do double pre-evac but we use single. Haven't measured DO,TPO etc yet.
Incidentally there's an article/advertorial in latest Brewers Journal about a much chunkier canning line(CFT) with info graphics showing purging similar to yours.