Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs
Community Proposals
Community Proposals
tag:snake search within a tag
answers:0 unanswered questions
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
votes:4 posts with 4+ votes
created:<1w created < 1 week ago
post_type:xxxx type of post
Search help
Notifications
Mark all as read See all your notifications »
Q&A

Why is a plastic bag needed for sous vide?

+4
−0

I have read a bit about sous vide, which seems to be basically just boiling in a plastic bag. Well, boiling is not true since the temperature is lower, but why is the plastic bag needed? What difference would it make if you just put the meat in warm water without the plastic bag?

Bonus question: Why is the vacuum needed? Is that just for more efficient heat transfer?

History
Why does this post require moderator attention?
You might want to add some details to your flag.
Why should this post be closed?

0 comment threads

1 answer

+5
−0

Sous vide cooking has three essential steps which make it different to regular cooking:

  • Long-term low temperature precise cooking (you need appropriate kitchen appliances to do this)
  • Bagging the food you're cooking (with a plastic or silicone bag or some kinds of cans)
  • Vacuuming the bag

The bagging is to avoid osmosis. All biological cells have a lipid bilayer which gives these cells a semipermeable membrane. That means as soon as you submerge biological cells into water, osmosis starts to equalise the water concentration on both sides (sides referring to your water bath and whatever you put into it).

An example of this is a normal soup. By putting vegetables in it, they will soak with water (due to osmosis) and get a little bit softer. In the process of this, the original structure of the vegetable in question is changed and so does its flavour. In soups, this is what you want to do. You want some chewy bits of vegetables, meat or anything else but you also want that the broth you use taste differently than plain water. The flavour is diluted.

With sous vide, you don't want to have this. You want to retain the original flavour so you bag whatever you're doing. This is especially important for meat and fish as both taste considerably different when soaked with water. So putting meat into your water bath without a bag will lead to the meat soaking itself up with water - now you have a watery piece of meat which tastes great in a soup but if you're not preparing a soup, the taste is off.

Vacuuming your bag isn't really a strong requirement expect if you truly want to have everything perfect. Vacuuming is all about thermal conductivity as you already noted. (But not in the sense that a vacuum can transfer heat especially well, actually it's a perfect insulator for conduction and convection while radiation is still possible.)

In sous vide cooking, heat is transferred primarily through conduction: Your food is in direct contact with the plastic bag which is in direct contact with the water. Little air pockets within the bag hinder a perfect conduction of heat so your food is unevenly warmed. That's the reason why you would want your bag to be vacuumed: to get an evenly heated surface.

My personal experience is that a perfectly vacuumed bag is nice to have but not absolutely necessary - the step from frying your food to preparing it via sous vide already makes a considerable difference in taste, structure and optical appearance even if it's not vacuumed. Vacuuming provides the final touch.

History
Why does this post require moderator attention?
You might want to add some details to your flag.

0 comment threads

Sign up to answer this question »