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Hello. I have been brewing for a few months and your advice has been extremely valuable. Thanks.

I have a question about glass bottles such as this one in the photo. I bleach them between use and have noted that some have developed this bubble pattern, which is permanent. Is it due to a coating on the glass? Is it hazardous to use these?

Thanks for your help


  • 1
    Are these re-purposed beer bottles? What was in them originally?
    – JPicasso
    Commented Mar 15, 2017 at 20:18
  • These are repurposed beer bottles. Lager was the original inhabitant
    – Rob Lee
    Commented Mar 20, 2017 at 16:00
  • I will break one to inspect the inner surface. Looking from the outside though, it looks like bubbles within the glass
    – Rob Lee
    Commented Mar 20, 2017 at 16:13

2 Answers 2


Have not had this happen to me, are you certain this is a change in the glass and not something being stuck on it?

I would be tempted to break one and get a closer look/feel/scratch.

I do notice that you are using clear glass bottles this is in general not considered good practices for beer as the hop has a substance that under light will turn into the same substance that skunks spray out. Not certain that this has anything to do with those bubbles tho.

  • Is there any reference for the idea that hop ingredients can be photoconverted to an isocyanate (skunk spray)? Photoconversion of hop oils can happen, but not (to my knowledge) to an isocyanate. Commented Mar 15, 2017 at 13:36
  • I had to do a search for that. Not certain if this is strongly disputed thing or not, and i have stepped in a hornets nest now. I did not find scolarly articles on this but here is one latimes.com/food/dailydish/… Not certain if the compound they report is isocyanate. Commented Mar 15, 2017 at 13:54
  • Did a bit more research according to the wikipeia article on skunks ther are tree main compunds in skunk spray isocyanate was not mentioned. but 3-methylbut-2-ene-1-thiol was, and it is referenced in the LAtimes article as a compound created when hops is exposed to UV Commented Mar 15, 2017 at 15:06
  • @barkingpete...nope. Skunk spray is mercaptans.
    – Denny Conn
    Commented Mar 15, 2017 at 15:58
  • My Bad. Isocyanides smell as bad as it gets but aren't actually produced by skunks which apparently produce thiols (mercaptans). As for the photo-degredation of iso-humulone, one can read full details here: eurekalert.org/pub_releases/2001-10/uonc-ucf101701.php Well spotted Elvish! Commented Mar 15, 2017 at 19:05

When I cleaned demi-johns and glass bottles by soaking in a solution of PBW and hypochlorite bleach I noticed a build up of some insoluble compound on the surface of the glass that looked similar to the photo above. Some sort of hard, waxy substance that was relatively difficult to scrub off. I have since stopped using bleach and all my newer bottles are OK. One neat way to sterilise demijohns (if you have a unit big enough) is to microwave them.

Does vigorous scrub with a demi-john bottle brush and a cleaning agent like PBW do anything? it may be worth trying if previously not attempted?

  • I have read elsewhere that microwaving does not work. Can you give a source saying that it does? Commented Mar 16, 2017 at 0:58
  • I rinse my demi-john. Drain it quickly of loose water and microwave. 60s in an 800W is my usual time. I suspect the presence of water which heats up on the surface of the vessel is the main factor. Not sure if it would be an efficient process with a totally dry vessel.I suppose it would be worth qualifying/redefining "sterilise" in the above answer to "with this method I have not suffered a biological contamination in 6 years of using it". E.g. I have brewed using lactobacillius/SCOBY and then brewed with yeast without apparent cross infection using this method. It seems a workable method. Commented Mar 16, 2017 at 8:03

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