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benjamin163

Question for sous vide boffins about vacuum sealing at different %

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Hello,

My chamber vacuum sealer can expel air from the bag at anything from 20% to 96%.

I usually seal everything at 95%.

I'm wondering why you would want to seal something at less than that.

Is there a good reason?

Is it simply so that you don't squash delicate food?

Or is there a more scientific reason?

Any help gratefully received.

 

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During the time when the Cooking Issues blog was active, Dave Arnold and Co. did a lot of tests with vacuum.  They concluded that using high pressure usually resulted in poor texture - for most meats, I think I remember them saying that 70% was best, but my memory could be completely wrong on that.  At high vacuum, the liquid inside the meat boils at room temp or even refrigerator temp, which alters the texture once cooked.

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Here's the piece at Cooking Issues.. The vacuum levels in KennethT's post above are much too low. 90% was the lowest vacuum level they tested. The takehome points are that robust meats like beef and lamb don't suffer much, but the texture of chicken and fish do (fish moreso than chicken). Sealing the protein with oil seems to help. But lower vacuum levels -- 90% -- were strongly preferred for chicken and salmon.

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The problems with texture aren't primarily caused by crushing but by rapid boiling of water in the protein at low pressures. Sealing your proteins when they're very, very cold can help with this. But there are some textural problems with squishier meat that are brought on by having the bag press down on it. That's where some mushiness can come from.

 

If you want to avoid crushing while vacuum sealing, get a chamber vacuum that has a "gas flush" option. These pull a vacuum on your bag but then fill it with inert gas before sealing it up so that the atmosphere doesn't crush your product when it floods back into the chamber.
 

Speaking for myself, I don't really feel the need to pull a vacuum on fish because I'm never sealing to store it for extended periods. Or cook it for more than like 30 minutes. I don't even seal the bag most of the time... just clip the top to the cambro to keep it from swimming away. For everything that I do pull a vacuum on, I end up sealing at whatever the maximum pressure my VP112 achieves is. And it's mostly robust stuff like beef and pork where there's no texture loss from high vacuum. I'm not really a big fan of sous vide chicken; I'd almost always rather do something else with it. SV turkey, on the other hand...

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1 hour ago, btbyrd said:

Here's the piece at Cooking Issues.. The vacuum levels in KennethT's post above are much too low. 90% was the lowest vacuum level they tested. The takehome points are that robust meats like beef and lamb don't suffer much, but the texture of chicken and fish do (fish moreso than chicken). Sealing the protein with oil seems to help. But lower vacuum levels -- 90% -- were strongly preferred for chicken and salmon.

Whoops!

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much appreciation for these answers.

I'm not so worried about crushing and the like. I'm mostly cooking tough cuts of meat which will withstand it.

I really wondered if having more air in the bag would lead to shorter shelf life issues.

Does the shelf life of a pasteurised pouch sealed at 80% differ from one sealed at 95%?

I'd love to take out less air on certain pouches because, as you rightly pointed out, many ingredients tend to bubble at 95%.

But I don't want to compromise shelf life or pasteurisation.

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I don't understand how a little air would compromise shelf life or pasteurization.  And as I recall many fish are designed to withstand tremendous pressure.

 

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My main concerns with extra air in the bag are primarily about food quality rather than bacterial spoilage, although part of the reason you're vacuum sealing is to create an environment that's hostile to aerobic microorganisms. But if you're also cooking sous vide at times and temps that are long enough to pasteurize, I don't think it makes a huge difference (though I may be wrong about that). Once you've killed the microbes, you've killed the microbes. But another aspect of spoilage is lipid oxidation. More air = more oxygen = more oxidation = rancid food and "off flavors." And if you're freezing, extra air in the bag invites freezer burn.

 

Concerns about "shelf life" are largely academic to me in this instance because I'm almost never vacuum packing delicate items with the intention to cook SV to pasteurization and then chill and store for extended periods.  You aren't -- or you shouldn't -- cook fish for long enough to pasteurize anyway. And I sort of think sous vide chicken isn't all that awesome compared to other ways of cooking chicken. Everything else is robust enough to handle a strong vacuum.

 

Do you have a particular application in mind? What needs a low vacuum level yet also is conducive to cook -> chill -> store SV practices?

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The main reason for vac sealing is getting the surface of the meat in contact with the plastic so it cooks evenly. Doesn't need to be  a vacuum at all, which is why the displacement method is just fine. Sealing does keep things neat and keeps SV bath water out of the bag.

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The question was about vacuum levels for cook -> pasteurize -> chill -> store SV workflows. The displacement method only works for cook -> serve workflows. Vacuum packaging offers a number of additional functional benefits in the first context.

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Again, thank you for these great replies.

@btbyrd, I'm thinking of things that I don't want to be 'moulded' when they come out of the pack.

I'm experimenting with 'ready meal' spaghetti and sauce. All pre-cooked then packed and pasteurised.

But when it comes out having been packed at 95%, the pasta is rigid and blocky.

That's one application.

But in general I was just wondering why these other levels of vacuum even existed and if I'm missing out on something.

I think you have explained very well that a lot of it is about texture which makes a lot of sense.

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