Vacuum foam compression question

[NoelW]

So i noticed a recipe for a 'sorbet' in modernist that involves putting it through vacuum in a sealed mason jar and freezing. My question is how does one do that and prevent the inevitable compression? We use a MVS45, i tried simply unplugging it after the mb went to zero or jar was full, but i couldnt get machine open without plugging it back in, which caused immediate compression. I wasnt ready to do any prying of sorts to see if you could even do that with it unplugged. Or do i simply have the wrong machine? Any help is always greatly appreciated.

on a side note i also tried this with a marshmallow to see if it would stay unbelievably huge at high pressure but of course would compress when plugged in...

[mkayahara]

Welcome to eGullet, NoelW! I'm not sure I understand what you mean by "compression". Are you talking about the fact that the foam will collapse if you draw too much of a vacuum? My understanding of the process - though I haven't had a chance to try it out yet - is that you need to be able to stop the vacuum pump when the foam reaches the right expansion. Can your vacuum sealer not do that?

I know there are a couple of others here who have done the mango sorbet, with mixed success. Maybe they'll chime in.

[NoelW]

yes, when drawing a vacuum it starts at 1000 millibars and heads towards zero, while anything i put in there bubbles, rises, or both depending on the hydrocolloids present. even if i manually stop the process, the final step always results in all of the air being removed in one quick step, resulting in complete compression of whatever i have in there. I know we have a gas option, maybe there is another option that eludes the final step and leave things airy? Maybe i should consult the machines manual?

[KennethT]

Maybe I'm misunderstanding - but are you trying to expand the foam with a covered mason jar, or uncovered?

In theory, you should put the cover on the jar pretty loosely, so air can escape, and put the whole thing in the chamber. When the air comes back in, the pressure seals the mason jar, keeping the vacuum inside the jar even though the chamber is pressurized. Then tighten the ring seal on the jar and put in the freezer. Once frozen, you should be able to let air back into the jar without compressing the foam.

This is the same theory behind the aerated foie gras done by Wylie Dufresne... he uses a container with a one way valve and puts the whole thing in his vacuum chamber. When the air comes back into the chamber, the one way valve holds the vacuum inside his container and keeps his foie foam expanded. Then it goes into the refrigerator, where the agar and gelatin will set the structure so it is stable under normal pressure.

[NoelW]

that explains everything. i read in the manual that there is a setting for allowing a one way valve, the company must sell these devices separately. Myhrvold suggests that you "attach lids and rings, and close until just snug". the mason jar technique must be an alternative to the valve, i just havent succeeded yet. thanks again! I can only imagine the forum topics that will blossom as chefs around the world take stabs at Modernist recipes...

[KennethT]

have you seen the "Cooking with Modernist Cuisine" forum????