Why did all my jam "fall" to the TOP of the jar?

March 1, 2011 7:21 PM

Why did all my jam "fall" to the TOP of the jar? I got some store-bought jam, used it once, then put it in the fridge. The next time I went to use it (about 2 weeks later), all the jam was moved to the top of the jar, up against the lid, as though it had been stored upside down. At the bottom of the jar was an empty gap. What caused this?

- It was organic apricot jam, no unusual ingredients (I no longer have the jar but I remember the ingredients were fairly standard), in a typical glass cylindrical jar, before the expiry date.

- I am 100% certain that it was not actually standing upside-down in my fridge or that someone else flipped the jar.

I got rid of it in case it was some weird bacterial outgassing action.

posted by (alice) to food & drink (20 answers total)

Maybe closing and opening the door shut multiple times on the fridge caused the jar on the shelf to shake and it's contents inside to slosh about thus having it stick to the top?
posted by littlesq at 7:57 PM on March 1, 2011

I've had this happen too, but I've assumed it was simply that someone flipped the jar upside down for a while, then uprighted it sometime later, leaving the jam stuck to the lid.

But that begs the question, who would put a jam jar in the fridge upside down?
posted by robotot at 8:11 PM on March 1, 2011

Had you perhaps set or held the jar upside-down (or dropped it slightly) right before you placed it in the fridge?
posted by astrochimp at 8:52 PM on March 1, 2011

Thanks for your ideas so far!
- I don't think door movement would cause this. No other jars were affected and things are packed in that compartment quite tightly.
- Again, the jar was in there 2 weeks between uses, so I don't think anything I did before putting it away would have done it.

The bottom of the jar was absolutely clear of jam and the top was full, no gaps. So weird.
posted by (alice) at 9:06 PM on March 1, 2011

My guess would be that the jam is warm before you stick it in the fridge. As it cools, it shrinks, and for whatever reason it cools from the top down (maybe because the refrigerator vents above it). The top jam shrinks and pulls a bit on the jam below it. Then they jam below it shrinks and pulls up the jam below it. So on and so forth until all the jam is cooled and has been pulled off the bottom.
posted by sbutler at 9:36 PM on March 1, 2011

I tend to store "natural" peanut butter upside down, to encourage the oil that separates out to percolate up through the solids. I offer this as a reason one might habitually store a jar with its lid down. Though it doesn't sound like the case here.

I feel like I've seen the phenomenon you describe, but after checking, none of my jams are currently levitating in their vessels.

P.S.:Apricot is the best jam. A wise choice however it comports itself when the fridge door is closed.
posted by mumkin at 10:14 PM on March 1, 2011 [4 favorites]

Is it possible that what you describe as an empty gap was actually clear liquid? Perhaps the mixture separated with the solids rising to the top, leaving water or juice at the bottom of the jar. This might appear to be an empty gap, especially if the glass had an odd texture, a label or otherwise wasn't perfectly transparent. I only ask because it seems like it would be tough to physically confirm the gap at the bottom of a jar of jam with a ton of jam blocking your access at the mouth of the jar.
posted by Jeff Howard at 2:04 AM on March 2, 2011

Okay, I'm going to take a shot. Note that I only know of "physics" as a word, but...

Let's pretend you've got your jar of delicious jam, and you've put it on your toast/loved one, and now it's going back in the fridge. But - UH OH! - you haven't put the lid back on properly. WHAT HAPPEN?

In my brain, I see jam pushed to one side of the jar. If you're right-handed, you likely remove jam with a knife using a right to left motion starting from the outer circumference of the jam jar. Jam is highly viscous, I know that much. So basically you're pushing jam to the left, from the right:

* -Densely-packed jam
** -Less densely-packed jam
*** -Even less!
**** -Most undensely-packed jam

Now the lid goes back on (perhaps not properly) and the jam jar goes back in the fridge. Now, in my mind, highly viscous materials like to cling to their kith and kin as much and as often as possible. So you've got air moving into the jar (and having trouble escaping, because the rim is sticky...air gets stuck on stuff, right?) and all this densely-packed jam at the top, and this less densely-packed jam at the bottom. Remember the viscosity!

** -Jam starts doing this?
**
***
***

Now I know jam isn't lighter than air, but remember you've got all this air down the right side of the jar, and all this jam down the left. Dense jam at the top. Maybe this happens?

**** -Disco jam!
***
**
*

And eventually you get to a point where you've got this:

**** -Hover-jam!
***
***
AIR

Well? What do you think? Yeah I've been drinking. Drinking SCIENTIFIC DISCOVERY!
posted by tumid dahlia at 2:35 AM on March 2, 2011 [11 favorites]

The most likely explanation is that someone really did turn the jar upside down at some point. But if that's not the case then perhaps the jam solidified and then started giving off gas - either because it was going bad or from some chemical reaction. Gas at the top of the jar escaped; gas at the bottom couldn't escape so it pushed the mass of jam upwards.
posted by Joe in Australia at 3:09 AM on March 2, 2011 [1 favorite]

Chipping in to say that a similar thing happened to me one with a jar of lemon curd; can't remember whether that jar had ever been upside down, but once up stayed up for weeks. The viscosity of the substance obviously creates enough surface tension to defy gravity.
posted by Diablevert at 6:07 AM on March 2, 2011

Reading a bit about canning I'd guess it was left out awhile the last time it was used it so it warmed up. When done the cap probably wasn't screwed back on supertight, leaving a bit of space for air to pass. As it cooled in the fridge it then underwent the same vacuum process in canning but at lower overall temps, pulling the jam up at the same time as it pulled the lid down.

Replicating it would probably be hard as you'd have to screw the lid back on just right. An easier way may be to try using a mason jar filled with the same amount of jam, allowed to sit at room temp for awhile (for the sake of the experiment, all day), and then putting them in the fridge and not opening it for an extended time (over night).

Not sure where you are but external temps may play in (i.e. Summer heat wave with no AC, winter, etc.). The top of the jar and lid may also need different amounts of jam on them too (leaving a bit clean for the air passage/vacuum effect). Probably wouldn't hurt if the jar's interior walls were coated either.
posted by jwells at 6:28 AM on March 2, 2011 [3 favorites]

I'd put money on it being gas formation from yeast growth; you were right to throw it away. Especially likely if the jam is low-sugar; not high enough to inhibit growth. Did it smell a bit yeasty/boozy perhaps? The top layer of the jam acts as a seal, like a syringe plunger, pushes up as gas is formed below. Seen this many times in the lab with agar-sealed broth tubes.
posted by Mundungus at 8:27 AM on March 2, 2011 [1 favorite]

I vote for the gas-formation hypothesis. Gas pushing up from below is much more credible to my mind than anything else.
posted by exphysicist345 at 9:46 AM on March 2, 2011

Well, at least I've learned this has happened to others, so it wasn't some kind of polterjam.

sbutler: Is that really a thing? I guess it's possible. I usually refrigerate jam even before first use because fruit and fruit products that aren't chilled are just too cloying for me. But I used this for a marinade so I think I may have left it at room temp before opening. It's pretty cold here right now but this could still account for your theory, I think, jwells.

mumkin: I tried to make a "compotes itself" joke but since that isn't funny at all, I'll just agree with you (and sour apricot would be even better!).

Jeff Howard: while that's in the realm of possibility, it just didn't look to be the case here.

Mundungus: I should have smelled it but, fearing an animated jam attack, I never opened the jar. One vote for gas, plus two more from Joe in Australia and exphysicist345.

If Diablevert ate levitating curd and lived to tell the tale, perhaps I should've kept my jar. I'm leaning more and more toward the gas idea, though, and who knows if it was safe.

Thanks again, everyone! But enough about jam. I want to go drinking with tumid dahlia.
posted by (alice) at 10:23 AM on March 2, 2011

> In my brain, I see jam pushed to one side of the jar. If you're right-handed, you likely remove jam with a knife using a right to left motion starting from the outer circumference of the jam jar. Jam is highly viscous, I know that much. So basically you're pushing jam to the left, from the right:

* -Densely-packed jam
** -Less densely-packed jam
*** -Even less!
**** -Most undensely-packed jam


I'm sorry, but I think the compressiblity of jam is probably quite low... :-/
posted by StarmanDXE at 10:33 AM on March 2, 2011

*shakes fist*

Damn you, compressability!
posted by tumid dahlia at 1:04 PM on March 2, 2011

Is that really a thing? I guess it's possible.

Hell if I know. Not really a jam person :)
posted by sbutler at 1:01 AM on March 3, 2011

boing boing had it happen too. maybe.
posted by misterbrandt at 3:25 PM on May 2, 2011

Heh, thanks for the update. The jam in the photo looks just like mine did -- totally stuck to the top, completely clear on the bottom.
posted by (alice) at 4:11 PM on May 4, 2011

I was reminded of this thread few weeks ago when, in a grocery store in Hawai’i, I noticed that all the jars of one particular flavor of jelly — Ohana Chili Pepper Jelly, I think — had levitating contents. These were obviously unopened, and presumedly manufactured in a commercial kitchen under sterile conditions, so I'd imagine that both stirring and contamination could be ruled out. Too, while the grocery was somewhat airconditioned, it was nowhere near refrigerator temperatures. Probably more like 70°F.
posted by mumkin at 6:46 PM on June 9, 2011