Reducing gas exchange in storage bottles to keep liquids fresher

PeterB · Nov 10, 2013

I mixed up a fresh batch of Dektol stock solution (3.8L=1 gallon) and filled up two x 2.0 Litre PET bottles. I squeezed them before tightening the lids to expel the remaining 100mL of air in each one.
One bottle kept its compressed shape but the other slowly expanded again as air leaked in through the less than perfectly sealed lid. I tried tightening the lid and using other lids to no avail. Then I decided to use some teflon (plumbing) tape to seal the thread. Et Voila ! No more air leaking into the bottle !

I know you're probably thinking, why not just get smaller bottles, or even use an inert gas to fill the space above the developer? Well as Dean Hutton from the curiosity show used to quip, "I'm glad you asked". The reason I prefer this teflon tape idea now is that:

1. Eventually when I use the stock and do need to fill up the bottle with an inert gas (my preference over marbles and accordion bottles for example), I can know for certain that the gas will exchange at a much slower rate. This method tests the (very tight) seal using a constant negative pressure.
2. I'm not a fan of accordion bottles or more than two different sized bottles

Unless you have a very tight seal then surely using an inert gas will give you a false sense of longevity. Here are two photos. One showing the teflon tape being applied prior to screwing the lid down tight, the other showing the PET bottle slightly squashed by 100mL. When wrapping the tape, ensure some overlaps the lip of the bottle as this will press against the inside of the lid.

So what do you think ?

mgb74 · Nov 10, 2013

I've had a partially filled, tightly stoppered PET bottle stay carbonated for weeks, so it may be a factor of the quality of the cap seal and/or uniformity of the bottle mouth. As you point out, negative pressure "invites" gas permeability.

I assume the teflon tape needs to be replaced after one or two openings. I might prefer an appropriately sized O-ring or rubber washer.

PET bottles do differ in their gas permeability. Dead Link Removed (not common but can be found) are usually less permeable than other PET bottles.

markbarendt · Nov 10, 2013

In order for the sense of security to be false with inert gas held at a pressure equal to the air outside the bottle there would have to be a significant tendency toward diffusion through the seal or bottle. That tendency is very low with good quality bottles. Even with minor imperfections the real exchange of air for inert gas will be exceedingly low.

A vacuum in your bottle though, is a significant driver of diffusion, as you have proved. It may be a reasonable test of bottle quality but is intrinsically unsafe.

MattKing · Nov 10, 2013

I bet that the teflon tape modified bottles would be less likely to leak liquid if they are knocked over.

markbarendt · Nov 10, 2013

One of the purposes of using teflon on pipe threads (tape or liquid) is to reduce friction, it makes it easier to get steel pipe joints tight enough along with filling imperfections. This is not necessarily a benefit on bottle cap. It becomes too easy to turn and allows over torquing which will deform the cap and the cap may not ever build enough pressure to fully crush the tape.

Kevin Caulfield · Nov 10, 2013

PeterB said:
I know you're probably thinking, why not just get smaller bottles, or even use an inert gas to fill the space above the developer? Well as Dean Hutton from the curiosity show used to quip, "I'm glad you asked".

Wow, that takes me back. I used to love The Curiosity Show.

PeterB · Nov 10, 2013

markbarendt said:
It becomes too easy to turn and allows over torquing which will deform the cap and the cap may not ever build enough pressure to fully crush the tape.

Possibly, however this will be picked up quickly in my method as the air flows back in under the negative pressure. Even if negative pressure poses less favourable conditions as it encourages the air to flow in. at least one could initially see if that happens. If it doesn't (over some period - say 1 day) it means the seal is very effective so you can then opt not to use negative pressure by partly twisting open the seal again to equalise the pressure then re-seal it. Alternatively fully open the seal, squirt in your favourite inert gas then reseal it.

I need to think more about the rate of diffusion/effusion through a tiny hole large enough to leak under negative pressure but supposedly not permit diffusion at a significant rate when the pressures are equalised in/out of the bottle.

PeterB · Nov 10, 2013

Kevin Caulfield said:
Wow, that takes me back. I used to love The Curiosity Show.

Yeah my kids now love it too. The presenters Dean and Rob only recently obtained the rights to their shows and have started putting them up on YouTube !

PeterB · Nov 10, 2013

mgb74 said:
PET bottles do differ in their gas permeability. Dead Link Removed (not common but can be found) are usually less permeable than other PET bottles.

You raise an important point to consider that the Oxygen is penetrating the PET walls ! I wonder how the rate of diffusion compares between different PET bottles and also to glass.

http://www.labthinkinternational.com.cn/literatures/permeability-testing-of-pet-beer-bottle.html

PeterB · Nov 10, 2013

http://www.quark-magazine.com/pdf/quark07/140BEERINPETPACKAGING.pdf

polyglot · Nov 10, 2013

At least just get a fresh PET (softdrink) bottle with a good lid. Don't use (LDPE) accordion bottles; the plastic itself is permeable and the ribs are impossible to wash.

Best solution I've found so far is the aluminised mylar bladder, commonly found when buying 10L bag-in-box water. You buys your water, make up the developer with it and then put the developer back in the bag. As you use it up, the bag deflates and there is never any air in there. Perfect keeping properties so far as I can see. Chuck the bag+box after a couple of refills before the tap starts to drip.

PeterB · Nov 10, 2013

polyglot said:
Best solution I've found so far is the aluminised mylar bladder, commonly found when buying 10L bag-in-box water. You buys your water, make up the developer with it and then put the developer back in the bag. As you use it up, the bag deflates and there is never any air in there. Perfect keeping properties so far as I can see. Chuck the bag+box after a couple of refills before the tap starts to drip.

What a great idea polyglot !! I've heard it before but now can appreciate exactly why. Ilford used to sell paper developer in 5L casks with this bladder inside

I just checked out the shelf life of wine in these bladders and industry aims for a minimum shelf life of 9 months.

It is still relatively short (compared to glass and cork) because "oxygen transmits through the film and tap at different rates depending on what type of plastics are used and has an unopened shelf life shorter than bottled wine"

Shawn Dougherty · Nov 11, 2013

PeterB said:
I mixed up a fresh batch of Dektol stock solution (3.8L=1 gallon) and filled up two x 2.0 Litre PET bottles. I squeezed them before tightening the lids to expel the remaining 100mL of air in each one.
One bottle kept its compressed shape but the other slowly expanded again as air leaked in through the less than perfectly sealed lid. I tried tightening the lid and using other lids to no avail. Then I decided to use some teflon (plumbing) tape to seal the thread. Et Voila ! No more air leaking into the bottle !

I've done the same thing with Saran Wrap in the lid and had no problems.

polyglot · Nov 11, 2013

PeterB said:
What a great idea polyglot !! I've heard it before but now can appreciate exactly why. Ilford used to sell paper developer in 5L casks with this bladder inside

I just checked out the shelf life of wine in these bladders and industry aims for a minimum shelf life of 9 months.

It is still relatively short (compared to glass and cork) because "oxygen transmits through the film and tap at different rates depending on what type of plastics are used and has an unopened shelf life shorter than bottled wine"

Yeah, nothings going to beat a closed glass bottle. But this is better than an opened glass bottle half-full of air!

I keep my Xtol stock in these bladders and it lasts for 9 months (maybe longer; I've always used it up in less than that time) with absolutely no change in performance.

Gerald C Koch · Nov 11, 2013

I posted a table of the permeabilities of several plastics to oxyg3n and carbon dioxide. PET compares very favorably with glass. Remember that the integrity of the cap is also important. Roughly the relations in order of preference are PET > PVC > HDPE > LDPE.

PeterB · Nov 12, 2013

Gerald C Koch said:
I posted a table of the permeabilities of several plastics to oxyg3n and carbon dioxide. PET compares very favorably with glass.

Thanks Gerald. For some reason the Beer manufacturers think there is a sufficiently large difference between glass and PET. Beer is very susceptible to oxidation in comparison to soft drinks. It concerns the beer makers enough to spend lots of time and money researching/testing/making special multi-layered PET. Refer to the links I gave in post 10 above for a summary of one company's work. Also post 9 has an interesting link.

Gerald C Koch · Nov 12, 2013

Here is a quick repost of the table I mentioned in a previous post. You can see that EVOH is the best choice and LDPE the worst choice with regards to oxygen permeability.

O2 CO2
---------------------------------------------------------
|EVOH |Ethylene vinyl alcohol copolymer | 2 | - |
|HDPE |High density polyethylene | 2900 | 9100 |
|LDPE |Low density polyethylene | 7900 | 42500 |
|PC |Polycarbonate | 4700 | 17000 |
|PET |Polyethylene terphthalate | 95 | 240 |
|PVC |Polyvinyl chloride | 120 | 500 |
---------------------------------------------------------
values are for 1 mil thickness, units cm3/m2.24h.atm

Sorry for the problem with proportional font and spacings but the table is readable.

mgb74 · Nov 12, 2013

Interesting. If I understand correctly, PET is much less permeable than HDPE.

I took a look around the darkroom and found:
Delta plastic bottles are HDPE
HC110 bottle is HDPE
Rodinal bottle is marked PE PA
Nalgene is HDPE

Which raises the question, why do manufactures and Delta1 use HDPE? I'm sure that it's sturdiness must be a factor.

But we're missing a critical piece of info for practical use. Gerald's table is based on constant thickness of 1 mil. But what is the thickness of PET and HDPE bottles as typically used? HDPE bottles are typically thicker; but I doubt that it would overcome the differences shown in the table.

mgb74 · Nov 12, 2013

polyglot said:
Best solution I've found so far is the aluminised mylar bladder

I've read, on Backpacking forums, that the wine and liquid bladders used in Australia are better than the ones we find here in US. No personal experience.

I wonder about the bladders used by Starbucks and other coffee shops.

polyglot · Nov 12, 2013

HDPE is more permeable for the same thickness, but I think you'll find the bottles are much thicker. All the HDPE bottles I've seen in the darkroom (developers etc) are about 1mm thick or more whereas PETE softdrink bottles are often under 0.1mm. I think the crack/shatter-resistance and general ruggedness of HDPE is also in its favour.

Andrew4x5 · Nov 12, 2013

Hi Peter
I notice that you are using non-pressurised (fruit juice?) bottles. I only use pressurised ('fizzy drink') bottles, typically 1.25 litre ones. I've never had any problems with the caps on these bottles or their caps. Apart from being smaller, the caps are made a slightly more rigid plastic and are designed to keep gas in - and therefore keep gas out.

I use these fizzy drink bottles to store ID11 and Bromophen stock. From experience, I've found that ID11 has a reliable storage life of four months (in warm Sydney, Australia). In the case of Bromophen, the storage life is longer - say six months - partly because you have the option of increasing the print contrast.

PeterB · Nov 13, 2013

Andrew4x5 said:
Hi Peter I notice that you are using non-pressurised (fruit juice?) bottles. I only use pressurised ('fizzy drink') bottles, typically 1.25 litre ones. I've never had any problems with the caps on these bottles or their caps. Apart from being smaller, the caps are made a slightly more rigid plastic and are designed to keep gas in - and therefore keep gas out.

Hi Andrew, Thanks for the tip. Yes I am using fruit juice bottles and you make a good point that the soft drink bottles would have a better cap seal. however after polyglot's suggestion I'm going straight for the mylar bladders !

Andrew4x5 · Nov 14, 2013

I have used bladders in the past - wine bladders actually! They are quite good, especially for larger quantities. If you are using bladders other than wine, make sure they are aluminised because non-aluminised ones (used for some fruit juices) do NOT keep out oxygen, as I found out to my cost. Also, you need to buy bladders with taps that you can easily remove, i.e. the style which is one piece, slips over the 'mouth' of the bladder, and has a tab in the centre tap that you lift to release wine/developer. The other style of tap, which is pressed into the mouth of the bladder is a PIA to remove. Unfortunately, I have forgotten which brands of wine had good or bad taps - old age and alcohol have blurred my memory!

Gerald C Koch · Nov 14, 2013

I think it is instructive to realize that wine supplied in bladder containers is meant to be consumed soon after purchase. These are the vin ordinaires or table wines. Better grade wines are supplied in glass bottles and can be stored for longer periods. I think this says quit a bit about using bladder containers for developer storage.

mgb74 · Nov 14, 2013

Gerald C Koch said:
... I think this says quit a bit about using bladder containers for developer storage.

But we often cellar wine for 2 years or much more. How long do we "cellar" our D-76?

Reducing gas exchange in storage bottles to keep liquids fresher

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