more thoughts on PET versus glass permeability

Following from a previous thread on PET versus glass, I observe that the concensus seems on the whole to be thus:

Glass is better than PET for long term storage, because PET is felt to be more permeable to oxygen than PET.

If that sums things up correctly, I would like to ask about the following consideration:

Is it not the case that rubber is hundreds of times more permeable than either, and thus the degree to which a long-term storage wine oxidizes in the carboy is really not significantly altered by the vessel, since most of the permeation of O2 is going to occur through the rubber?

Your thoughts?

Sean

Reply to
snpm
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I don't recall seeing any study that would confirm your assertion.

If it is true, though... regard the surface area where the permeability would occur. 3-4 square inches at a bung, or massively more over the surface area of a carboy.

Kirk

Reply to
Kirk Mitchell

Fair point, but I suppose it depends on the ratio. I have emailed better-bottle to see if they have any more specific stats for internal carboy surface area and 02 exchange across the PET material.

I can't help thinking that if the PET walls truly do suffer only 'negligible' 02 permeability, by definition they are as low risk as using a rubber bung (which probably has greater permeability but lower surface area). Interesting thread though :)

Jim

Reply to
jim

About as much permeability as a barrel? Less I think.

better-bottle to see if they have any more specific

02 permeability, by definition they are as

lower surface area). Interesting thread

The Anchorage Fishwrapper and Litterbox Liner Press

Reply to
A. J. Rawls

I hadn't even considered the permeability of barrels, good point :)

better-bottle to see if they have any more specific

02 permeability, by definition they are

lower surface area). Interesting thread

Reply to
jim

yes thats really an excellent point...surely barrels are much much more permeable than glass?

A. J. Rawls wrote:

better-bottle to see if they have any more specific

02 permeability, by definition they are as

lower surface area). Interesting thread

Reply to
snpm

Actually it's more complicated than that for a sealed barrel. The barrel is semi permeable and it is now thought that it actually pulls ambient air into the wine in tiny amounts because a vacuum is created on tightly bunged barrels. They consider this micro oxygenation and it's good for reds. As to whether a better bottle would emulate that, I guess it comes down to surface area and permeability. To be honest, I don't know if they think the air comes in from toppings or through the staves; I have seen both stated. Smaller containers have more surface to mass ratios, if you wanted to emulate anything i would guess the 30 to 55 gallon barrels would be the ones to go for. Maybe Google micro oxygenation and wine or barrels.

Joe

Reply to
Joe Sallustio

Yes, I thought the surface area to volume ratio would be a big influence on how much the stored wine is affected and that is another point well raised!

However, if Better Bottles really do have negligible permeability to O2 then they are likely to cause less sealed storage oxidation than a hypothetical barrel of of similar internal capacity or larger. I draw this conclusion because barrels don't have negligible permeability. I wondered if the following extract is useful?

"Oak barriques soften wine by diffusing 20 to 30 mg. (15 to 23 ml.) of air-oxygen per litre of wine per year (mg/l/yr) through their micro-porous staves. This natural osmotic permeation is driven by the higher partial pressure of oxygen outside (0.2 atm) to inside the barrel (~zero), as wine "consumes" all the available oxygen that diffuses in. Permeation provides MOST of the oxygen entry into a barrel. Repeated topping only adds about 5 mg/l/yr and splashing/racking about

4 mg/litre each time. Successful wine maturation requires an "oxygen rationed" environment, rather than "all at once" oxygen exposure, which instead promotes oxygen catalyzed acetaldehyde formation and aerobic bacterial spoilage i.e. by Acetobacter, always present in small populations in wine (unless sterile filtered). Smaller barrels allow oxygen to diffuse in at a faster rate per litre of wine in them than larger barrels, due to their higher surface area to contained volume. Metal tanks allow no permeation, instead requiring micro-oxygenation.

4mm thickness of the special C-P polyethylene used in these vessels, diffuses oxygen from the air at about the same rate as 20mm of new Oak. However it is a one way effect. The C-P material is absolutely taint-free and does not allow evaporative loss of wine components so these vessels DO NOT NEED TOPPING."

This quote comes from a metal fermentation container manufacturer so you could expect a bias in that direction. This is page though has some useful information on oxidation at several stages in different containers though - I don't know if it is contentious.

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Food for thought all of it, Jim

Reply to
jim

Reply to
RomeoMike

Am I the only one who finds it a little odd that there is no obvious evidence-based practice with this?

RomeoMike wrote:

Reply to
snpm

Isn't this a pretty new product? I don't remember seeing ads for them before 2 years or so. That's not enough time to get any decent aging data.

Pp

Reply to
pp

Their website will have been registered 4 years in April it seems.

Jim

Reply to
jim

I don't know if this is of general interest, but here is the reply I had back from better bottle regarding permeability and oxidation. I must say it sounds fair...

" Substantial, and rapidly growing, numbers of home winemakers and brewers, as well as suppliers of kits, clearly prefer Better-Bottle's unique PET carboys and fittings to glass carboys. Nevertheless, anecdotal reports of oxygen diffusing through the walls of Better-Bottle carboys and causing poor results pop up from time to time and we are asked to comment.

Making a good wine or beer is something of an art and occasionally results do not meet expectations, regardless of whether the winemaker or brewer uses a glass carboy or Better-Bottle carboy. It is impossible to draw any valid conclusions from anecdotal reports of sporadic, subtle failures, because identifying the cause rigorously is usually impractical. Absolutely, using carboys made from any of the common plastics that scalp flavors and are quite permeable to oxygen will guarantee an inferior result. However, it would be a mistake to assume that using a glass carboy will necessarily guarantee a superior result. Rubber stoppers, especially silicone stoppers, most common types of flexible tubing, and liquid-filled air locks can leak lots of oxygen. Moreover, oxygen diffuses so quickly through beer and wine that removing a stopper from a carboy, even briefly, for testing and making adjustments can allow a great deal of oxygen to enter. Racking from one open carboy to another open carboy with a siphon, a pretty standard approach when glass carboys are used, will essentially saturate the wine or beer with oxygen. Yes, traces of oxygen can diffuse through the wall of a Better-Bottle carboy, but experience indicates that the impact is negligible and more than offset by a wide range of advantages. "

Jim

Reply to
jim

from better bottle regarding permeability

I'm laughing so hard at the initial BetterBottle reply that my side hurts... This is marketing hype at its best.

Brief exposures of the wine to air as occurs during racking is consumed by the wine and SO2 in a day or two. That is unlike the constant resupply by oxygen diffusion through a container. From my understanding, it's more like leaving excess headspace in the container.

Oh well, I'm a Doubting Thomas. I know my cranberry juice oxidizes within a year in its PET container. Is it through the lid seal or through the PET... I haven't run the experiment to find out. But I know PET is not a great oxygen diffusion barrier, so unless there is/are additional layers of good oxygen diffusion barrier material in the BetterBottle, I'd think twice about long term wine storage in a BetterBottle.

Gene

Reply to
gene

I think you'd still be in a vast majority in feeling that way.

Being a newbie I haven't yet reconciled why wineries don't usually seem to bulk age beyond a few months but home wine-makers do?

Personally I believe the hype on their product for the way I am using it. I am planning to send everything to bottle within 3 months of fermentation ceasing. I have yet to hear someone come forward and say they have had a positive experience with long term aging in Better Bottles though, so I suppose that weighs in for the neigh-sayers so far.

Gene, I wonder if you have you stats on PET and diffusion to refute their claims that it is of negligible permeability? I fully accept that statistics don't matter if you are finding that Better Bottles don't work for you!

Jim

from better bottle regarding

This is marketing hype at its best.

wine and SO2 in a day or two. That is

understanding, it's more like leaving

year in its PET container. Is it through

But I know PET is not a great oxygen

diffusion barrier material in the

Reply to
jim

bulk age beyond a few months but home

am planning to send everything to bottle

forward and say they have had a positive

weighs in for the neigh-sayers so far.

claims that it is of negligible permeability?

Bottles don't work for you!

from better bottle regarding

This is marketing hype at its best.

wine and SO2 in a day or two. That is

understanding, it's more like leaving

year in its PET container. Is it through

But I know PET is not a great oxygen

diffusion barrier material in the

Can't find the table of diffusivities in a hurry, but here's a reference from University of Guelph, Canada, Food Technology Center, in which PET is mentioned not being the best oxygen barrier:

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Here's an interesting article about modifications to PET to improve oxygen barrier properties:

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Gene

Reply to
gene

I just found a table with some polymers oxygen diffusivity.... PET better than polycarbonate, but worse than HDPE and polypropylene.

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One of the better oxygen diffusion barriers is Polyvinyl Alcohol (PVA), but it doesn't make for a very strong container, so typically would be used as a layer on the inside of the bottle. My polymers handbook is packed away, so this'll have to do for now.

Gene

jim wrote:

bulk age beyond a few months but home

am planning to send everything to bottle

forward and say they have had a positive

weighs in for the neigh-sayers so far.

claims that it is of negligible permeability?

Bottles don't work for you!

from better bottle regarding

This is marketing hype at its best.

wine and SO2 in a day or two. That is

understanding, it's more like leaving

year in its PET container. Is it through

But I know PET is not a great oxygen

diffusion barrier material in the

Reply to
gene

For those that haven't actually touched a Better Bottle, the plastic used is rigid, unlike a PET pop bottle. They're more like the V8 plastic bottles that we get in Canada (and probably the US, but I'm not certain).

I know that this doesn't answer the permeability question, but results from storing wine in PET pop bottles may be different from Better Bottles.

age beyond a few months but home

Not sure what commercial wines you're buying, but in local (BC Canada) liquor stores many of the reds being sold are from 2002-2003-2004. Yes whites are from 2005, may be even 2006 if from the southern hemisphere.

Steve

Reply to
Steve

Thanks for the information Gene, it was useful if not hard reading to a non chemist but appreciated! It does indeed spell out that standard PET is far from O2-tight :)

I think Steve picked up on a useful point there though. The Better-Bottle.com website does suggest, albeit a little mystically, that BBs are made from a 'special PET' with negligible permeability. In scanning the pdf articles I saw that Anna Polyakova says it IS possible to produce a PET which is 'considered impermeable' via two stated methods.

I am not sure then whether discussing the properties of standard PET applies as Steve said. On paper it is down to whether Better Bottles 'special PET' is one of these improved types or standard PET. I currently expect the latter.

Jim

bulk age beyond a few months but home

Reply to
jim

Good eye, Jim. Yes, it is possible to lower the oxygen permeability of PET as Anna Polyakova (cute name for someone working with polymers, BTW). I'll dig for that patent application info, but I'm disappointed that Better Bottle hasn't put the oxygen diffusivity numbers in their technical specifications page for us to VERIFY their claim, not imposing upon us to pay for the testing that they should use to validate the claim in the first place. We're not all 'Bayer Aspirin' trusting souls, lol.

The stiffness of the PET has much to do with the degree of crystallinity (i.e. cross-linking) of the polymer as part of the polymerization process. The more cross-linking, the stiffer. The pop bottle PET is more flexible primarily because it has less cross-linking. In polymer science terms that is a 'lower average molecular weight' polymer. So better bottle is higher average molecular weight.... that alone can be the basis of a claim of 'special PET'. I'm not saying the BB is bad. I still am a Doubting Thomas because there are not cold, hard oxygen diffusivity numbers published by BB to back their claim. I've been a materials scientist qualifying materials into manufacturing processes too long to take my supplier's claims at face value. It is buyer beware in the world of suppliers.

Gene

jim wrote:

chemist but appreciated! It does indeed

website does suggest, albeit a little

permeability. In scanning the pdf articles I saw

impermeable' via two stated methods.

as Steve said. On paper it is down to

standard PET. I currently expect the latter.

bulk age beyond a few months but home

Reply to
gene

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