Oxygen Absorbing Caps

Earlier this year Ashton Lewis participated in an “Ask Mr. Wizard” Q&A on BYO’s Facebook page where questions flew in over a two-hour timeframe. He provided quick and concise answers to over 30 questions. What follows is his original, short answer (in italics), plus some more information he wanted to provide when given additional time to expand on his thoughts.

Not 100% sure what the crown liners contain, but do know they work. Plenty of data and anecdotal evidence shows that these special liners reduce oxygen ingress and help to scrub oxygen from the headspace. Two common chemistries used to give polymers oxygen-scavenging properties are the inclusion of iron or ascorbic acid in the polymer mix. These compounds bind oxygen, and that’s basically how they work.

The topic I did not mention in my original answer was oxidation in general, and especially oxidation associated with bottle filling. Much has been written in the homebrewing literature about hot side aeration in the brewhouse and splashing of beer causing oxidation during racking, but there seems to be less written about oxygen pick-up during packaging. The truth is that oxygen pick-up during packaging can very quickly ruin great beer and is certainly a topic worthy of serious head scratching.

In the commercial world of brewing there are really two types of bottling operations. Small-scale fillers that operate in the 2–50 bottle per minute range and rotary fillers that typically are designed to run in the 100–1,000 bottle per minute range. The modern rotary filler incorporates bottle pre-evacuation techniques, bottle fill control, and fobbing immediately before crowning to keep oxygen pick-up during filling to amazingly low levels. Many breweries using these sorts of fillers routinely have 50 parts per billion or less of oxygen in bottles after filling. This is really low. These brewers are happy campers.

Slower speed fillers are typically designed for smaller breweries with budget constraints, and many of the technological features common in modern rotary fillers are either less sophisticated in these slower machines, don’t work as well as the faster machines, or are simply not part of the design of the machine. This means that air pick-up is almost always higher, often by a factor of 10, compared to faster and more sophisticated fillers. This is pretty high. These brewers are often times bothered by bottle air.

It seems obvious that these small breweries should just buy fancier technology if they are really concerned about air pick-up, right? Obvious, yes. Easy, no; the difference in cost between these technologies starts at about $100,000 and can quickly be over $1 million. That’s why many small breweries use bottle crowns with oxygen absorbing liners. While these special liners can help small breweries with less than adequate bottle fillers, they cannot perform miracles.

These special crowns are also used by breweries with modern fillers because of oxygen ingress. This happens when oxygen from the environment slowly equilibrates with the carbon dioxide headspace of a beer bottle. Oxygen scavenging crowns help to prevent oxygen from making its way into the headspace and prolonging beer shelf life. So that is why this question brings up an important point worthy of further explanation.

Response by Ashton Lewis.