Should vegetables be stored in the bag they came in?

The perforated bag from the store is less packaging than a humidity setting: it holds the moisture building up inside and lets the excess escape through the holes. That setting protects some vegetables and makes others sweat and rot. So there is no single rule that fits all vegetables; the split is made by what humidity the vegetable wants.

What is the bag actually setting?

A vegetable keeps losing water after it leaves the soil. What we call wilting is largely the result of that loss, and a closed environment slows it down.

But in that same closed environment the moisture the vegetable gives off has nowhere to go. It condenses on the inner surface of the bag, turns into droplets and collects at the point where it touches the vegetable. That is usually exactly where spoilage starts.

The job of the holes is to strike a balance between these two extremes: to let some of the collected vapor out without losing all the moisture. So what decides things is not the bag itself but the air inside the bag.

The crisper drawer is designed for this job anyway; it holds more humidity than the rest of the fridge. When the air inside the bag and the air in the drawer work in the same direction, the vegetable keeps for a long time; when they work against each other, the bag undoes the drawer's work.

Which vegetables keep better in a bag?

Vegetables that want humidity, with thin leaves and a wide surface, keep noticeably longer in a bag. Leafy greens, broccoli, cauliflower, carrots and celery stalks are in this group; left out in the open they wilt quickly.

Even in this group the mouth of the bag is not closed fully. A bag left ajar holds the moisture but lets the vapor collecting inside escape; the same balance works for storing greens.

Putting a folded paper towel inside the bag sets up the same balance. The paper draws off the excess moisture and keeps droplets from touching the vegetable; changing it every few days is enough.

Which vegetables rot in a bag?

Vegetables that want a dry, airy place sweat in a bag. Onions, garlic and potatoes are in this group; in a closed bag they soften, sprout and pass their smells to one another. Their place is a ventilated container or an open basket.

Mushrooms spoil quickly in a bag too; a paper bag suits them better, because paper draws off the excess moisture. The relationship between tomatoes and the fridge is a separate question and is covered in the article on keeping tomatoes in the fridge.

Items such as cucumbers and peppers sit in between. They can stay in a bag, but if a wet point of contact forms, that place starts to rot; drying them before they go into a container is usually enough.

Is this different from fruits affecting one another?

It is different, and separating the two makes things easier. The effect between fruits is that the gas given off by a ripening fruit speeds up the one beside it; its subject is proximity, and it is covered in the article on which fruits should not sit next to each other.

What is described here is the moisture balance inside the packaging; it applies even when a single vegetable is sitting on its own. A closed bag magnifies both: it holds in both the moisture and the gas. So a bag tied tightly shut is the worst option for most items.

What can you do today?

After shopping, you can look inside the bags before putting them in the fridge; opening the mouth of the ones that have misted up, or putting a paper towel inside, is a one-step correction.

Sorting the bags rather than throwing them away helps too: the ones that want humidity stay in the bag, the ones that do not come out. Once that split is made, it repeats itself on later shopping trips.

Drying items that come home wet before they go into a container is the last step. Water on the surface is the first thing that starts spoilage, whichever bag is used.