Article on cardboard odors

[Drax]

We have had other topics discussing storage methods for pu'erh, so I thought some people might find this interesting.

There was a recent article in the Journal of Agriculture and Food Chemistry (Czerny and Buettner, Faunhofer Institute for Process Engineering and Packaging) that looked at odors from cardboard, as well as wet cardboard.

The researching found that the "classic woody cardboard smell" comes from 2-Nonenal (both E and Z, or "cis" and "trans" if you prefer, are present). Plus they said one "unidentified compound" (hmm). (btw, read the wiki article on the compound for a good chuckle about "old lady/man smell").

They identified 36 total compounds, including a lactone that smells of peach, and a phenol that gives a "horse stable-like" quality.

Most importantly, the researchers note that only some of the compounds release from the surface of dry cardboard. They surmise that the others are sort of "locked in" with the cellulose in the inner part of the cardboard -- then when it gets water, the water helps release those compounds, making a stronger odor.

Bottom line, I suppose, should have been obvious anyway -- keep your cardboard dry! But that means a bit of balance is needed for those who 1) use a pumidor or 2) are in a humid environment.

[woozl]

Interesting side note,
A "corked wine" is caused by 2,4,6-trichloroanisole (TCA)
http://en.wikipedia.org/wiki/Corked_wine
TCA is the damp moldy cardboard smell.
Yet, it is also the same quality we enjoy in Basmati rice.

[Intuit]

Topic already posted by me, this thread
Puerh>Source for Plain Wrapper?
http://www.teachat.com/viewtopic.php?f=20&t=11236&
http://www.sciencenews.org/view/generic ... nse_scents

Fungi and bacteria are cellulose degraders.

[Drax]

Ah, cool! Sorry about the double post, then. Maybe it'll be more eye-catching in a thread with a title that specifically mentions it.

In any case, still makes me wonder about storing beengs or tuos in the boxes they come in (particularly XiaGuan items). . .

[Intuit]

Agreed. Your cautionary is necessary and useful. Many pu'erh collectors use low-grade quality cardboard for storage and employ pans of water or wet sponges for humidification that may cause pockets of high humidity that can be readily absorbed by cardboard. Pretty sure there is a good reason that bamboo leaves are the preferred medium for tongs packaging.

OMTP may clarify whether or not he feels that the presentation boxes you mention present a potential source of odors. Their value may be purely resale/provenance related and maybe best kept separate from their contents. :unsure:

Maybe we can find cheap bamboo-cardboard boxes.

[betta]

To my knowlege, the experiments carried out by Fraunhofer Institute were done by first soaking the entire cut carton pieces into tap water (leaching) and followed by extraction. Here we talk about the oversaturation region (>100% humidity of the humidity diagram, which is nonexist because it's no longer called humid), in which the behaviour of the carton could be completely different than if we are at humidity below 100%.
For puerh storage, people used to work at below 85% humidity and any temperature. As long as we don't reach the oversaturation (>100%) region (below dew point) in the humidity curve, there won't be any condensation in the storage.
And thus we won't be getting (extracting) those odor molecules into our pu, unless there's direct contact of pu with liquid-form water and carton at the same time (like in soaking or condensation).
The extraction can only happen when the substance is in contact with liquid or supercritical form solvent.
I presume the research was intended for cartons used for take out delivery, such as take out box, in which oil, fat and whatever liquid are directly in contact and adhere to the carton. Thus this liquid really does able to extract the odor molecules.
Honestly the molecules the people claim to have caused the odor have at least above 180-200°C boiling point. Their vapour pressure at normal ambient temperature should be almost negligible and the transfer of these molecules to the food should mainly only due to extraction.

[Drax]

And thus we won't be getting (extracting) those odor molecules into our pu, unless there's direct contact of pu with liquid-form water and carton at the same time (like in soaking or condensation).
The extraction can only happen when the substance is in contact with liquid or supercritical form solvent.
I presume the research was intended for cartons used for take out delivery, such as take out box, in which oil, fat and whatever liquid are directly in contact and adhere to the carton. Thus this liquid really does able to extract the odor molecules.
Honestly the molecules the people claim to have caused the odor have at least above 180-200°C boiling point. Their vapour pressure at normal ambient temperature should be almost negligible and the transfer of these molecules to the food should mainly only due to extraction.

Certainly you're going to find more stuff extracted if you soak the cardboard in water. However, I don't think you can assert that no extraction will occur unless if it's in contact with the liquid. How much instead? I don't know (but see below about detection limits).

It also suggests an additional problem of 'wet-storing' a beeng.

As Intuit mentioned in the other thread, one might have some concern about tea oils and the like. Given that cakes usually aren't dripping in oil. it's not clear how much of a problem this might pose.

Finally, vapor pressure is not the thing I would be worried about here. I would be most worried about the human detection limit for smell and taste -- because that's the bottom line. It doesn't matter if a high boiling point compound has a low vapor pressure, if it still is detectable, and some of these things have extremely low (e.g. parts per trillion) detection limits in humans.

[betta]

Certainly you're going to find more stuff extracted if you soak the cardboard in water. However, I don't think you can assert that no extraction will occur unless if it's in contact with the liquid. How much instead? I don't know (but see below about detection limits).

It also suggests an additional problem of 'wet-storing' a beeng.

As Intuit mentioned in the other thread, one might have some concern about tea oils and the like. Given that cakes usually aren't dripping in oil. it's not clear how much of a problem this might pose.

Finally, vapor pressure is not the thing I would be worried about here. I would be most worried about the human detection limit for smell and taste -- because that's the bottom line. It doesn't matter if a high boiling point compound has a low vapor pressure, if it still is detectable, and some of these things have extremely low (e.g. parts per trillion) detection limits in humans.

Drax, thanks for keeping us informed.
Yes, you're right that we should take into account the detection limits in human.

The possibility is always there, however when there's no liquid "solvent" involved, then we are talking about diffusional mass transfer involving solid-solid, with D tends to zero (thus in literature, the binary diffusion coefficient of solid-solid is seldomly discussed). So it is theoretically possible, but practically very slow, maybe at the rate close to that of geological reaction?

I am thinking of the possibility that the odor substances contaminated the cake as the result from mass transfer from gas phase to solid (puerh) phase. Therefore vapor pressure is important, providing this is the case.
But unfortunately this might not be the case, unless microbial activity really manages to crack those odor molecules into smaller molecules with higher volatility.
Please keep us updated about this because it is interesting for all of us. I myself am no longer storing my pu in cardboard simply because I've bought a large plastic container which is more mobile.
Instead of facing cardboard odor problem, now I have an issue of condensation and danger of mold growth