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Old 01-25-2012, 04:40 PM   #1
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Default oxygen permeability of plastic

I don't know why the hell I do this kind of stuff and stir up the usual HBT flamers, but here goes anyway. I read an article that I thought was interesting and I thought I would share it.

I want to make a couple of things clear from the get-go:

1. Yes, lots of people ferment in buckets and do just fine.
2. Yes, lots of people ferment in buckets and win bjcp comps.
3. Yes, you ferment in a bucket and your beer is awesome.
4. If you like your beer and you ferment in a bucket, great. Soldier on.
5. If you ferment in a bucket and notice some premature staling, then this thread is for you.
6. Yes, I am sure this topic has been beaten to death, but what the hell. This forum is for discussion, isn't it?
7. If you are just going to chime in to flame, then don't bother. You don't add anything to the conversation.
8. If you are just going to chime in to say that I don't know what I am talking about because I am not a premium supporter, then don't bother.
9. If you are only going to chime in to say that "we have beat this topic to death and we aren't discussing it anymore" than don't bother. Only those who want to discuss it, should discuss it. If you don't want to, then don't. It just adds a lot of BS posts for the rest of us to weed through.
10. If you are going to pick and choose which lines to read in this post rather than reading the whole post for what it is(just sharing information) in order to create a straw man which you can then proceed to knock over and show your superior intellect, then don't bother.

Now that the required HBT controversial topic disclaimers are out of the way....

http://www.foodinnova.com/foodInnova/docu2/322.pdf

I am sure I'm not the only one who has seen this article on oxygen permeability for plastic containers used for fermented beverages. According to the research that they did for this paper, they found that in a 190L HDPE tank, they were able to record 2.15mg/L of dissolved oxygen per month making it through the walls of the container.

Now a 190L container has much more surface area than a ~24L(~6.5 gallon). Just converting that down linearly would equate to .2688 mg/L of dissolved oxygen making it through the bucket per month into the beer. Now there may be some variables that alter this number slightly, but it should be close enough for discussion's sake. If my math is correct, this would equate to 268.8 ppb of dissolved oxygen per month absorbed into the beer for every month of storage. In a personal conversation with Dave Berg, head brewer at Schell's brewing, he stated that you want under 50 ppb of dissolved oxygen to help prevent premature beer staling.

I know that the yeast may take up some of this oxygen even after fermentation is complete, but I suspect that they don't take up all of it.

I have a very low taste threshold for oxidation in my beers, and I was noticing some premature oxidation character in my beers while I was using plastic buckets. Sure, I won some comps with those beers, but maybe my taste threshold is lower than some people for oxidation. I have since switched to glass and that oxidation character has disappeared.

As always YMMV, and do whatever you think is good for you. I just wanted to share this information.



Let the flames begin...

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Old 01-25-2012, 05:15 PM   #2
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I know that the wine industry has several options, and among them are HDPE tanks specifically designed for oxygen permeability.

Their material and construction probably differs greatly from the HDPE buckets most homebrewers use.

The article you present specifically mentions, "...they may have a controlled
permeability, which makes their use more attractive for the cellars."


Further: "In this work it has been analyzed the Oxygen Transfer Rate (OTR) in a controlled permeability 190L HDPE wine tank (Flextank, Australia) by an analysis of the uniformity of the dissolved oxygen (DO) distribution. Non-invasive and non-oxygen consume optoluminescence technology has been used for the analysis of the spatial distribution of the DO concentration, as it is essential to know and control the process. It has been done the control of the same red wine aged in HDPE tanks and in barrels simultaneously, to analyze and compare the differences between the two aging systems."

So I wonder if using this article as a basis for understanding the O2 permeability of bucket fermenters is really appropriate?

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Old 01-25-2012, 05:22 PM   #3
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Where I work we have a tolerance of 300ppb in the bottle (force carbed, no yeast), we put an 8 month shelf life on our core beers.

We'll make sure what's in the tank is under 50ppb (often under 20), but the dodgy Italian bottling machine likes to add oxygen. Last week the run of 8000 bottles I did was averaging 130ppb (I measure every half hour).

We use stainless tanks obviously, but it just goes to show how easy it is to introduce nasty stinking oxygen down the line.

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Old 01-25-2012, 05:31 PM   #4
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+1 to homercidal's comment about the container used in the study not being comparable to the container used in homebrewing.

I also wanted to comment on this:

Quote:
Originally Posted by MachineShopBrewing View Post
I have a very low taste threshold for oxidation in my beers, and I was noticing some premature oxidation character in my beers while I was using plastic buckets. Sure, I won some comps with those beers, but maybe my taste threshold is lower than some people for oxidation. I have since switched to glass and that oxidation character has disappeared.
I wonder if you could pick up the oxidation if you were blinded to the beers that came out of the buckets versus those that came out of the glass. My point being is that is tough to not taste something once you have a bias in mind.
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Old 01-25-2012, 05:36 PM   #5
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it takes a while for oxidation, at these low levels, to be detectable. i can go through a 5 gallon batch faster than any oxidation can so i don't mind if a bit of oxygen gets in my beer, if it even is getting in through the plastic. even if i did use glass or steel to ferment in i'm sure i'm getting some O2 in the beer down the line somewhere, so is everyone else. it's like trying to run between the drops during a rainstorm, you can either give in to it now or later.

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Old 01-25-2012, 05:37 PM   #6
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Quote:
Originally Posted by broadbill View Post
+1 to homercidal's comment about the container used in the study not being comparable to the container used in homebrewing.

I also wanted to comment on this:


I wonder if you could pick up the oxidation if you were blinded to the beers that came out of the buckets versus those that came out of the glass. My point being is that is tough to not taste something once you have a bias in mind.
exactly.
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Old 01-25-2012, 05:43 PM   #7
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Flextanks design is SUPPOSED to allow more O2. That is their selling point. I'm not arguing that HDPE is as good as glass, or even that you can taste the difference. I just think more information about your claims is needed.

Here is a chart showing the O2 permeability of various types of wine containers, from Flextank's Own brochure:



Note that racking twice allows more O2 than the HDPE tanks that are not designed for O2 permeability.

It's well known that HDPE is far ahead of any other food grade plastic, except PET, for Oxygen Permeability.

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Old 01-25-2012, 05:48 PM   #8
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Oh, and by using this chart we can assume a 6X greater O2 permeability over their previous HDPE vessel (which may or may not share permeability with the HDPE buckets we use...)

And by using your own number or 268.8 and dividing by 6 we get 44.8 ppb, which is comfortably less than the 50 ppb that Dave Berg from Schell's states is wanted to prevent staling.

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Old 01-25-2012, 05:52 PM   #9
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EDIT: nevermind I see the label at the bottom.

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Old 01-25-2012, 05:57 PM   #10
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Quote:
Their material and construction probably differs greatly from the HDPE buckets most homebrewers use.
This could be, as they don't really specify in the article. But, I am familiar with plastics and HDPE is pretty much the same across the board. Thickness may play a part in moving that number slightly, but permeability is permeability.

Here is another paper talking about the gas permeability of HDPE among other things http://www.plastics.org.nz/documents...fact-sheet.pdf


Quote:
Where I work we have a tolerance of 300ppb in the bottle (force carbed, no yeast), we put an 8 month shelf life on our core beers.
Suppose you had 100-200ppb and the 8 month shelf life on the bottle, at what point would you say that a lighter or hoppy beer would peak and start heading south when kept around 40F (~4.5C)? In your experience.


Quote:
I wonder if you could pick up the oxidation if you were blinded to the beers that came out of the buckets versus those that came out of the glass. My point being is that is tough to not taste something once you have a bias in mind.
I am confident that I could pick out the oxidation if it was indeed present. I can pick it up in commercial beers very easily if they have it. I actually didn't have a bias when I first started tasting it. I was tasting the oxidation first and then tracked it down to the buckets. I always keg with flushed kegs and I even flush my auto-siphon with CO2 when racking to the keg, so the pickup there should have been negligible.
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