Plastic (PET) Carboy vs. Glass Carboy | exBEERiment Results!

[denny]

@brulosopher

Sorry, I wasn’t clear-- I’m able to squeeze almost every last bubble out PET, while the glass retained more bubbles because I could only rely on shaking over my sanitizer bucket.

Thanks!

[blair.streit]

@denny

@brulosopher

This is likely a weak limb to try and explain the difference, but what sanitizer was used?

Glass always seems to clean up better than plastic. If star-san was used, it’s possible something was “left behind” in the plastic fermentor that was successfully washed out of the glass one.

Either way, I’d say that cleanliness is more of a concern for most brewers when choosing between glass and plastic, not oxidation. But that’s just my hunch.

I use glass. I can be more aggressive with cleaning techniques without having to worry.

StarSan. This is an interesting theory, for sure. I make sure to get as much out of my carboys as possible prior to filling with wort, which for my PET carboys involves gently applying pressure to shoot the bubbles out… you can’t do that with glass.

Star San has been noted to be a yeast nutrient in a minor way.  If that’s so, it would seem that the plastic batch, assuming it retained StarSan (which is a pretty long shot), would have had an advantage, not disadvantage, over glass.

So now we need a couple more xBMTs to compare “a little” residual StarSan versus none, and none versus the crap ton that you get if you cold crash while leaving the blowoff tube in the bucket of StarSan

[charles1968]

This might be relevant:

Scalping of Flavours in Packaged Food
http://tinyurl.com/hwcf4lu

[brewinhard]

@blair.streit

@denny

@brulosopher

This is likely a weak limb to try and explain the difference, but what sanitizer was used?

Glass always seems to clean up better than plastic. If star-san was used, it’s possible something was “left behind” in the plastic fermentor that was successfully washed out of the glass one.

Either way, I’d say that cleanliness is more of a concern for most brewers when choosing between glass and plastic, not oxidation. But that’s just my hunch.

I use glass. I can be more aggressive with cleaning techniques without having to worry.

StarSan. This is an interesting theory, for sure. I make sure to get as much out of my carboys as possible prior to filling with wort, which for my PET carboys involves gently applying pressure to shoot the bubbles out… you can’t do that with glass.

Star San has been noted to be a yeast nutrient in a minor way.  If that’s so, it would seem that the plastic batch, assuming it retained StarSan (which is a pretty long shot), would have had an advantage, not disadvantage, over glass.

So now we need a couple more xBMTs to compare “a little” residual StarSan versus none, and none versus the crap ton that you get if you cold crash while leaving the blowoff tube in the bucket of StarSan

Not that this really means much, but I leave quite a bit of starsan foam in my carboys when I rack my beer from the kettle into it.  So much so, that as the beer displaces the foam it pushes it out right out the carboy and up the outside of my tubing. It actually acts as quite the barrier from anything falling into my carboy opening as the racking is underway. Beers come out great…

[charles1968]

This table from the paper in link above shows how flavors from orange juice are “scalped” by various plastics - basically the plastics absorb nonpolar aromatic compounds including many of the oils that are found in hops. Some of the flavour compounds in orange juice will look familiar to brewers:

There’s only one para regarding scalping in beer:

[quote]For pale ale bottled in clear PET and PEN containers with plastic caps, and a glass control bottle with a crown closure, sensory, and physicochemical properties at the 14th wk, showed PEN bottles to have provided the best protection, followed by glass and finally PET (Goodrich 1997).
[/quote]

So glass is better than PET at preserving flavors. I’ve seen other sources saying that the plastic liner in crown caps can scalp certain hop aromas, but fortunately linalool (the sweet-smelling tropical terpene in Mosaic and Citra) doesn’t get scalped by crown caps or PET.

[jrdunne (Joe Sr.)]

How much does acidity affect flavor scalping?

OJ must be significantly more acidic than beer.  At least that’s my non-scientific assumption.

[blair.streit]

How much does acidity affect flavor scalping?

OJ must be significantly more acidic than beer.  At least that’s my non-scientific assumption.

The Google thinks your non-scientific assumption is pretty good:

[quote]Orange juice ranges in pH from 3.3 to 4.19. It has 122 calories, 139 percent of the DV for vitamin C, 12 percent of the DV for folate and 13 percent of the DV for potassium per cup. Its effect on tooth enamel, however, isn’t clear.
[/quote]

It’s not down in the mid 2’s with the colas, but it is significantly lower than most non-sour beers (remember, pH is a logarithmic scale so the difference between 4.5 and 3.5 is pretty significant).

Not sure if that would impact how it interacts with the plastic, but it seems plausible.

[skatz (Stevie)]

The chart is titled orange oil, not orange juice. Also missing the timeline.

[denny]

The chart is titled orange oil, not orange juice. Also missing the timeline.

Yeah, I’m skeptical of the equ8ivalence between this and beer.  Not to mention that beer stays in plastic only a week or 2 usually.

[charles1968]

Two weeks might be enough for a significant effect. My plastic fermenters still smell of hop weeks after thorough cleaning and bleaching, so I reckon some scalping does happen in an average fermentation. Also, note that some flavours get scalped quicker than others - the paper says that absorption of citrus flavours by LDPE (low density polyethylene) is “instantaneous”. I think scalping or contamination is the most plausible explanation for the exbeeriment result. I’m not convinced by the starsan theory.

[charles1968]

The chart is titled orange oil, not orange juice. Also missing the timeline.

True, but there,'s plenty of evidence of scalping from juice discussed in the paper too. The timescale is in the text:
“About 70% of limonene was lost from cold-pressed orange oil in contact with LDPE for 4 d”

Not that limonene is important to brewers. Also pH found to make no difference to scalping of limonene.

[skatz (Stevie)]

What about surface area? Was it five gallons of oil in a 5-6 gallon container?

I’m not crapping on what you found outright, I’m just pointing out where there could be differences.

My Better Bottles smell clean and they are 5+ years old. I used buckets for years, and yes, they did hold a bit of an aroma. This is partly why I’m hesitant to upgrade to Speidel fermenters.

Doesn’t Leos ferment in modified conical storage tanks?

[toby]

My Better Bottles smell clean and they are 5+ years old. I used buckets for years, and yes, they did hold a bit of an aroma. This is partly why I’m hesitant to upgrade to Speidel fermenters.

http://www.better-bottle.com/technical.html

[charles1968]

What about surface area? Was it five gallons of oil in a 5-6 gallon container?

I’m not crapping on what you found outright, I’m just pointing out where there could be differences.

My Better Bottles smell clean and they are 5+ years old. I used buckets for years, and yes, they did hold a bit of an aroma. This is partly why I’m hesitant to upgrade to Speidel fermenters.

Doesn’t Leos ferment in modified conical storage tanks?

It’s not my research so feel free to crap on it. The orange oil research paper is referenced in the bibliography in the link I posted.

PET is much better than other plastics as far as I can tell. It better be as I brew all my beers in it.

[pmorrissette (Phil_M)]

@charles1968

Two weeks might be enough for a significant effect. My plastic fermenters still smell of hop weeks after thorough cleaning and bleaching, so I reckon some scalping does happen in an average fermentation. Also, note that some flavours get scalped quicker than others - the paper says that absorption of citrus flavours by LDPE (low density polyethylene) is “instantaneous”. I think scalping or contamination is the most plausible explanation for the exbeeriment result. I’m not convinced by the starsan theory.

I completely agree that your theory sounds more plausible. I just brought up my starsan theory because it is theoretically possible. The starsan is merely another variable to consider.

[charles1968]

Another possibility is a false positive - it’s got to happen sometimes. That was my gut reaction until I remembered something I’d read about crown cap liners zapping hop aromas.

[denny]

@charles1968

Another possibility is a false positive - it’s got to happen sometimes. That was my gut reaction until I remembered something I’d read about crown cap liners zapping hop aromas.

How was that determined?

[charles1968]

A couple of references below. There’s a paywall in the way of the full paper but you can read the abstract. Sierra Nevada have done similar research into plastic linings in cans.

http://pubs.acs.org/doi/abs/10.1021/acs.jafc.6b00031?journalCode=jafcau

Sierra Nevada on the cans vs. bottles debate

[jonhughey_att.net (HoosierBrew)]

@charles1968

A couple of references below. There’s a paywall in the way of the full paper but you can read the abstract. Sierra Nevada have done similar research into plastic linings in cans.

http://pubs.acs.org/doi/abs/10.1021/acs.jafc.6b00031?journalCode=jafcau

Sierra Nevada on the cans vs. bottles debate | BeerPulse

Thanks for posting. I’d read about oxygen scavenging caps absorbing hop aromas before. My takeaway is to keep kegging as much as possible and only bottle hoppy beers when necessary (for comps, gifts,etc.). I do dry hopping in the keg which is a plus.

[charles1968]

Yes kegs probably give maximum hop aroma and quickest grain to glass time, which also helps avoid fading over time. You can get good results in bottles - perhaps just need a bit more dry hopping to compensate.