Silicon bung related?

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JBP

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I recently put new silicon bungs on 3 carboys, all wines over 1 year of age. Normal cleaning and sanitizing of bungs prior to use, wines had fresh dose of k-meta at the time the new bungs were inserted. After 3 months, two of the carboys had developed a layer of gunk or foam in the neck of the carboys -several other carboys in the same area with standard airlocks are all normal. More interestingly, one of the problem carboys was a gallon jug with an exact mate (same wine, same location) with a standard airlock and no gunk - these jugs are a 3+ year old wine from juice that I was just never able to make good enough to drink, so have been using down the original five gallons as cooking wine, vin brûlée and homemade red wine vinegar (made and stored in a totally different part of the house).

The problem wines smell fine - I racked the good one and added k-meta. I still have the one gallon jug with the gunk/foam as I thought I might try to figure out what it was or what is causing it (not a valuable gallon as I have more than enough cooking wine and vinegar).

I have never used silicon bungs before and find it curious that only those carboys had the issue. An N of 2 is not much - perhaps just coincidental or odd luck. Any thoughts?
 

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* The look of your gunk would make me concerned about an aerobic microbial infection. (many colonies are white though). Has the flavor changed?
* My look at the silicone bung is that it is two piece construction. If you clean the flap that forms the top it is possible to get paper fibers stuck creating an open channel. I don’t clean new bungs. I minimize cleaning of silicone to carboys which had excessive foam enter the silicone bung.
* On a two year old wine why not use a solid bung? or ,, I use a single hole cork with a Granger check valve and pull a vacuum. I would like to degass and CO2 makes an inert headspace.
 
I have had similar issues but nearly as bad as yours with the vented silicone bungs. What I believe happened in my case was the little air in and out made environment favorable for microorganism growth but also I noticed my SO2 levels dropped a lot faster with the lose bungs compared to traditional air lock bungs leading to less protection on the wine. Now I use trade airlock bungs or a solid bungs ( no vents) with wire to hold the solid bung in place as temperature or pressure changes can pop a solid bung off.
 
Just a thought... what size are those vented bungs? If they are 6.5 or 7, they might be too big for the 1 gal jugs. I have been using vented bungs for a couple years (bulk aging around 1 year on a 3 month kmeta schedule) and have not had issues. I'm using them on carboys and the bungs are inserted nearly all the way to the top- so deep inside that they are actually difficult to remove. In your pics, you do not have them inserted very far into the necks. This might allow some air ingress.

Also, where are you storing them? If you have your wine stored in a place that sees wide temperature fluctuations, I could see some air being pulled into the jug/carboy when temps drop. The vented bungs are good but not perfect. Also, if the environment is musty with high humidity, there is always the chance that the air has more organisms (bacteria/mold) in it to infiltrate and propagate. There are obviously many factors that can contribute.

IMO, you would be better off by bottling after 1 year of aging. I don't see much benefit to keeping wine in a container that obviously has a higher potential for issues. It's not maintenance free- you need to keep adding chemicals and exposing the wine. More potential for bad things to happen. I would recommend against it unless you have no other options.
 
Just a thought... what size are those vented bungs? If they are 6.5 or 7, they might be too big for the 1 gal jugs. I have been using vented bungs for a couple years (bulk aging around 1 year on a 3 month kmeta schedule) and have not had issues.
I use vented bungs with Carlo Rossi 4 liter jugs. It takes a bit of finessing to them them in, and only 1/4" fits inside the jug mouth. However, I'd had wines in this situation for a year with no problems.

The valve on mine seal fine -- if the temperature drops, air cannot get in. The reverse is opposite, if temperature rises air will be pushed out, as can wine if the container is too full; however, this is normal behavior as the purpose of the valve is to let air out.
 
I use vented bungs with Carlo Rossi 4 liter jugs. It takes a bit of finessing to them them in, and only 1/4" fits inside the jug mouth. However, I'd had wines in this situation for a year with no problems.

The valve on mine seal fine -- if the temperature drops, air cannot get in. The reverse is opposite, if temperature rises air will be pushed out, as can wine if the container is too full; however, this is normal behavior as the purpose of the valve is to let air out.

Seems unlikely that air could get in under normal temperature fluctuations but doesn't seem impossible if the fluctuations are significant in range. Anything could leak under enough pressure/vacuum but I agree that it seems unlikely with this design if the bung is not compromised. Without being able to test these bungs with a vacuum, a person doesn't really know for certain.

Now that we are talking about this, I might build something out of pvc pipe to run an experiment on these bungs with a vacuum pump... 🤔

A more likely scenario is introducing something foreign during maintenance dosing. I wipe the tops of my carboys and bungs before pulling the bungs. There is always a layer of grime built up. My carboys are stored in a pantry and my wife's bedroom closet. There is always going to be stuff that settles on top and could find its way into the wine if not using good hygiene and techniques (especially in my wife's closet) 🤣
 
Seems unlikely that air could get in under normal temperature fluctuations but doesn't seem impossible if the fluctuations are significant in range.
It's really the opposite. In my stoppers (I have 2 types) the cap is flush on the main part of the stopper. If the outside pressure increases and/or the temperature decreases, this will contract the contents and move the ullage to more of a vacuum, which will pull the cap down tighter.
 
It's really the opposite. In my stoppers (I have 2 types) the cap is flush on the main part of the stopper. If the outside pressure increases and/or the temperature decreases, this will contract the contents and move the ullage to more of a vacuum, which will pull the cap down
I totally understand your thought process, Bryan. My theory is based on the vent cap design and it not being flat. On the bungs that I have, the vent cap bottom has a raised edge around the outer edge. I'm just speculating that I could see it warp and leak under a heavy vacuum. Seems super unlikely and thats why I think running a vacuum test would be interesting.

The OP obviously has an issue and others have expressed their concerns with these bungs. I haven't personally experienced issues and it sounds like neither have you but that doesn't mean the design doesn't have potential weaknesses. It also doesn't mean it does. I'm just playing devil's advocate on this topic.
 
Thanks for all the follow-up. I am in process of evaluating for microbial contamination - microscopic evaluation tomorrow and pending aerobic cultures. Other responses to questions in the discussion:
- The bungs are 6.5 - could be a little too large for the 1 gal jug, should be fine for the 5 gal carboy?
- Wine is stored in a MN basement - some fluctuation, although as stable a temp as I have anywhere. This occurred in the last 3-4 months (through heat(?) of summer, although it is Minnesota and it is a basement - more likely humidity changes
- no reason at all to store in carboy beyond 1 year - the good wine (a FWK Super Tuscan) was right at a year and "life" got in the way of bottling. Substituted the vented bung just to try it and thinking about potential fluctuations. The gal jug of 3+ year old wine was never bottled because it was never good enough to drink. A juice bucket that was just meh despite all my efforts. Could have used a solid bung, just didn't.
- The bungs had not been removed since being inserted 3 months earlier - they both had a slight but definite negative pressure seal when removed (fluctuation of temps?)

The ST has been racked and had K-meta added - will watch to see how it develops. The gal of "meh" is what I am "diagnosing" and may get tossed just because i have been messing with that batch for too many years and have plenty of it bottled/saved for cooking wine and other efforts. Will probably try the silicone bungs again at some point while also sticking to my standard plan of aging a year with airlocks, then bottling.
 
I've experienced the exact same problem multiple times (when using silicone vented bungs for long(er) term storage)... so much so that I tossed out all the vented bungs I had purchased and went back to using solid rubber bungs for all my wines in bulk storage.
 

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