Bottle caps.. who knew?

Posted by Homebrew Beer on

Many homebrewers begin their brewing careers by bottling their beer, and even after they eventually move to kegging, I talk to many who still bottle occasionally for competitions, to give away, or to take to parties, etc. So it seems that almost everyone is doing some amount of bottling. Like many other products in our shop, we have been looking at ways to reduce packaging and waste, and after a decent first run through our brewing water salts and cleaning products, it came time to reorder bottle caps. Now I admit I did this exercise backwards, since I ordered the caps in quantities of 10,000 (the standard pry off type), THEN looked into the difference between the pry off caps and twist off caps. If I had done the research first, I might have ordered differently, but in any case, here is what I learned..

Pry off caps can only be used on non-threaded bottles, but twist off caps can be used on either threaded or non-threaded. I ordered a very small quantity of the twist off caps so I could get a better look at what makes them different, expecting to find some physical difference on the inner edge that grabs the bottle threads, but I was surprised to find nothing. No difference at all, that I could see. Over to Google, and there I learned that the caps are physically identical, but the twist off cap is made from a softer metal that better grips the threads, and therefore seals better.

For months, I have been telling new homebrewers that unfortunately, using their old saved-up twist off bottles for their homebrew was not a good idea, since the caps on the market would not seal them effectively. I was both right and wrong. The caps we have in the shop will not suffice, as they are made from the stiffer, less pliable metal and should only be used on pry off bottles. However, if I had known that the twist off, better known as universal caps, would work on either, we might have just stocked those. In any case, we have 10,000 black and 10,000 silver caps in stock, soon to be repackaged, but we will add in some of the universal type, and if they prove to be as effective as the manufacturers claim, we will likely switch over to them in future. 

Side note: in discussing this with a colleague, he told me that he ONLY uses a bench capper for all his bottling, and after capping the bottle, he rotates the bottle 1/4 turn and applies pressure again. His assertion was that by doing so, he has never lost pressure in a bottle he capped. Seemed like a logical and simple tip to pass along, so consider it passed along...

The next area about bottle caps to learn about is oxygen absorbing versus standard. The difference is in the liner on the inside of the cap, and the oxygen barrier liner is made of a special plastic that contains elastomers, polyisobutylene and polybutylene, and it substantially improves the seal to further impede oxygenation. However, they cost more than the standard cap, and can easily and innocently be stored incorrectly, which negates their effectiveness. Since they are made to absorb oxygen, once the bag is opened, the liner begins to saturate with oxygen from the ambient air, reducing their effectiveness. After a bottling session, if they are not properly resealed (I envision having to vacuum seal the bag after each use) then they continue to absorb ambient oxygen in storage, and may be completely ineffective when you go to use them again. And finally, they appear to be employed mainly when long term storage is expected, such as many months to years. With many homebrewers I know, it's not a stretch to say that their beer is lucky to survive the weekend, so I suspect long term storage is generally not needed.  As I mentioned initially, many homebrewers bottle for awhile, then move to kegging, using bottles only for gifts, to transport to a party or event, or competitions. To me, all of these scenarios suggest that the beer will not be in the bottle long enough for the more effective cap to serve its purpose. Since the cost is higher and the use seems somewhat dodgy, I think we are going to stick with standard caps for now.

OK, last word on this subject. If you have read along up until now, you know we are going to move to buying caps in bulk and changing the packaging. We have decided to package caps in reusable zip lock bags of 60 instead of the one-use heat-sealed bags we use for grains. While this is still a plastic bag that will eventually find its way into our waste stream, being reusable at least gives it more of a life than just one use. Homebrewers are a very creative lot and I hope these bags will find other uses around the brewery.

Cheers, and thanks for reading...
Dean Rowan


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