Food Safety Issues/baking
I was wondering why baked goods that contain eggs do not need to be refrigerated after baking? However if we cooked eggs plain, say scrambled eggs, we would have to refrigerate leftovers. Why the difference? Thanks!
ANSWER: Hi Lauren,
This is a good question and I'll try to explain why one type of egg needs refrigeration and the other not.
First, raw eggs have everything that harmful bacteria need in order to grow -- a rich source of protein, moisture, the right pH and exposure to oxygen. When they are cooked such as scrabbled, not much has changed except the protein has been coagulated which has decreased the moisture but not to a level that doesn't support the growth of harmful bacteria.
When an egg has been baked it food items such as cake, cookies and brownies, the egg protein has been distributed throughout the product which greatly decreases the moisture content of both the egg present and moisture in the entire product. In fact, the moisture level decreases to such a level in baked goods that it does not support the growth of harmful bacteria. This is why a baked caked or cookie product that contains eggs can be left at room temperature after baking.
However, baked goods that contain a larger proportion of eggs and other moisture-rich foods such as milk, canned pumpkin, etc must be refrigerated after baking because the moisture content is still within the level that can support harmful bacteria. This is also why cooked, plain eggs must be refrigerated after cooking.
So it all comes down to moisture. If the moisture level is greater than .85 then it must be refrigerated in order for it to remain safe to consume.
Hope this answers your question. If you have additional questions, please let me know.
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QUESTION: Thank you so much! How do you judge moisture content? Is there a tool to do so? Thanks again!
Yes, there are a variety of tools and methods for determining water activity and moisture content in foods. Unfortunatley, it is not something that can be done outside of a food lab for precise measurements.
However, for drying fruits and meats at home a method used to determine if the food has been dried sufficiently to not support the growth of harmful bacteria (in the case of meat) or mold (in the case of fruit) is a process called conditioning. This involves taking the dried food and placing it in a sealed glass jar for 7 to 10 days. If condensation develops in the jar, the food has not been sufficiently dried and could support the growth of harmful bacteria or mold.
For a chart the outlines the moisture content in foods, please see: http://www.novasina.com/wDeutsch/doc/Produkte/Wasseraktivitaet/Fly-aw-Graph-DFE.
Also see: http://www.csiro.au/en/Outcomes/Food-and-Agriculture/water-activity-in-food.aspx