Why can baked goods like cookies and cake be left out on the counter that contain eggs, but scrambled or fried eggs would need to be refrigerated?
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Many factors are considered for food spoilage, but for this example, I give you the two main reasons:
1. Baking food kills a lot of microbes that can cause the food to spoil. So they stay good for longer.
2. In chemistry, there is a term called Activity of Water or Water Activity *(aw)* which basically means how much water is available for the microbes to use. Cooking and baking reduces the *aw* and helps the food stay good for longer. For example, when you make jam out of cherries and add a lot of sugar, the sugar reduces the aw. That’s why jams stay good for long periods of time.
Edit:
1. Thank you for the upvotes and awards. Please also award the OP themself, since a good question is more valuable than a good answer.
2. Water Activity is mostly influenced by osmolarity, which basically means how many particles are in the water. These particles can be anything, sugar molecules, Na and Cl ions (from salt), etc. So food does not have to be dry to have low water activity necessarily. If you add too many particles to food (A lot of sugar or a lot of salt), then water activity is reduced. Although, adding not enough sugar might actually make it spoil faster since it is a good food source for many microbes.
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It’s the water content. Water is life, also for bacteria. Plus, sugar is a natural preservative.
It’s the water content. Water is life, also for bacteria. Plus, sugar is a natural preservative.
As others have mentioned, it’s all about water.
You’ll notice that eggs that haven’t been baked can still be left in the shelf, provided they’ve had their water content reduced.
For example, powdered eggs, certain types of meringue or dried pasta.
So cookies can sit out for two weeks (and more); cooked eggs can only sit out for two hours. They are both “cooked”, right? Yes and no.
The cookies are made with sugar and some salt. They are also dried in an oven. The moisture in them is evaporated or locked up in the sugar and salt. Without ‘free’ moisture, it is hard for the bacteria to get going.
The eggs are all protein. The cooking changes the structure of the protein and dries it out some (or a lot if you cook the hell out of it), but most eggs still have some moisture. And they don’t have anything to lock up that moisture and keep it away from bacteria. So instead it provides a whole bunch of food + moisture for the bacteria to use to grow upon. If you leave the eggs out for two hours and come back to it, you’ll see that it has started to “sweat” somewhat, and that moisture provides a great home for bacteria.
Fun fact: you can let an egg sit out a very long time…by salting it. You can crack an egg yolk into salt and then cover it in more salt and it will preserve it. Eventually, a good bacteria shows up and it results in lactic acid on the egg, which preserves it.
Also, there are dried eggs – they are dried very quickly in industrial dryers and become “powdered egg” and can last 5 year.
Scrambled and fried eggs are only considered “loosely cooked” whereas baked goods with egg in are “well cooked”. Many people with egg allergy can tolerate well cooked egg but not loosely cooked egg – this is common in children (mostly they will “grow out of” the egg allergy).
Edited to add – my daughter (8 months) has an egg allergy. She tolerates well cooked egg but “loosely cooked” egg gives her a horrendous rash and triggers her eczema. I think the proteins change with cooking. The allergy clinic provide a list of well cooked/loosely cooked foods so you know what to give/avoid.
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