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Food & Dining

Why does boxed milk have cooked taste?

The Tampa Tribune
Published:   |   Updated: March 19, 2013 at 05:17 AM

Q: Why does the milk that comes in the little boxes on the shelf have a funny taste to it? And how does it keep so long? I'd like to keep some in the emergency supply box because the expiration date is so long, but my family complains that it tastes funny. The ingredients only say "milk," but are there other chemicals in there?

Answer: What your family is noticing is the "cooked" flavor of milk that has been heated to 280 degrees. Regular pasteurized milk is heated to only 160 degrees. That extra heat is why the milk in shelf-stable cartons lasts so long. Regular pasteurization heats milk just enough to kill anything that might make us sick.

However, there are often other bacteria that, while they won't make us sick, can sour or spoil the milk. These can survive 160 degrees. So to keep milk safe longer, that ultra-high-temperature or UHT milk is heated to 280 degrees for just three to four seconds. That's hot enough to kill the rest of the bacteria. But even that short time is enough to heat and slightly change the milk proteins.

We taste the change and call it a cooked flavor. If milk were not so mild and bland to begin with, we would probably never notice the difference. But there is nothing else in milk to cover up the cooked flavor. After the milk is heated to kill the bacteria, it is packaged into sterile containers and sealed in a sterile machine. So until the box or package is opened, the milk is safe. There is nothing in there to spoil it, which is why it can keep so long. Probably if you added a little chocolate or other flavor to it to mask the cooked taste, your family wouldn't object to having it in the emergency box.

Q: Why don't recipes specify if they can be frozen, or how long they would last if they were frozen? That's one of my big complaints about the TV cooking shows. The recipes look great, but they make more than I can use at one time, and I never know if I can freeze it or not.

Answer: It's hard to be precise about freezing mixed dishes. Part of the reason is all the different ingredients. Another reason is that the type of freezer makes a big difference in the quality of the food. Self-defrosting freezers are much more likely to cause freezer burn than deep freezers. The more often a freezer is opened, the poorer the quality of the food will be. Almost every food will be safe after being frozen; the quality is what suffers.

I can offer some general guidelines for you, but most have exceptions too. Boiled eggs will get tough, but eggs beaten into a batter and baked will be fine. Mayonnaise as a salad dressing will break down and get watery, but mayonnaise in a cake or used to hold breading on baked fish or chicken will do OK. Most sauces or gravies made with cornstarch or flour will break down if they're frozen. Sour cream separates when it is frozen. Cream won't whip as well after it's been frozen. Boiled potatoes, rice and pasta get mushy and taste warmed over. Pepper, cloves, garlic, green pepper, celery seasoning and some other herbs often get bitter or taste very strong after freezing. Onion, paprika and curry change flavors. Salt makes fats go rancid faster in the freezer. Imitation vanilla tends to turn bitter. Look at those changes, then at your recipe, and decide if you want to try to freeze it. It will be safe, but the flavor or texture might be different.


Mary A. Keith, a licensed dietitian and health agent at Hillsborough County Extension, can be reached at mkeith@ufl.edu.

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