So you made lasagna last night, and it was delicious. You saved the leftovers by wrapping aluminum foil over the top of the pan, and putting it in the fridge.

 

　　When you get hungry today, you go to look for that lasagna, but it looks like the lasagna was getting hungry too! It’s eaten tiny holes in the aluminum foil that was covering it.

 

　　Why does this happen?

 

　　A listener asked this question and we'll find the answer on today's moment of science.

 

　　There are really two things responsible for those holes in the aluminum foil: the acidic nature of the lasagna and some curious properties of aluminum.

 

　　Lasagna gets most of it’s acid from the tomatoes in its sauce. Almost everything you eat is at least slightly acidic, but tomatoes are especially so. This acid wouldn’t be a problem for a glass container, or stainless steel, or plastic wrap, or for most of the materials we use to store and prepare food. Aluminum, though, is especially vulnerable to acid.

 

　　Here’s why. Most metals form a protective layer on their surface called an “oxide layer.” Aluminum forms an oxide layer too, but it is very thin, allowing the tomato’s acid to easily break through. This lets the tomato sauce dissolve the aluminum, and it creates grey or black chemicals on top of the lasagna that taste very bad.

 

　　The same thing can happen if you use aluminum cookware for acidic sauces. Sauce made in an aluminum pot will be grayer and not as tasty as sauce made in other cookware.

 

　　饥饿的千层面！

 

　　你昨晚做了千层面，而且味道不错。吃完后，你将剩下的千层面用铝箔纸包好放入冰箱中。

 

　　今天当你饿的时候，便去找昨天吃剩的千层面，但是你会发现千层面似乎也饿了！包裹它的铝箔纸上出现一个个的小洞，好像被咬过一样。

 

　　为什么会这样呢？

 

　　一位听众问到了这个问题，我们将在今天的科学一刻中寻找答案。

 

　　铝箔上出现这些洞有两个原因：一个是千层面本身具有酸性，另一个就是铝具有一些非常奇特的属性。

 

　　千层面的酸性主要是来自所淋的番茄酱。几乎你吃的每样东西都会至少呈轻微酸性，而番茄的酸性尤为明显。这种酸对玻璃容器，不锈钢，塑料袋或大多数我们用于储藏和准备食物所用的材料都不会产生任何影响。但铝却非常容易受到酸的侵蚀。

 

　　原因是这样的。大多数金属会在表面生成一种叫做氧化层的保护膜。铝金属也会形成氧化层，但是这层膜很薄，番茄中的酸能轻易腐蚀透。由此番茄酱就会溶解铝，在千层面上产生一种灰色或黑色的化学物质，会使千层面变得非常难吃。

 

　　如果用铝制厨具来做酸味儿酱料，也会发生相同的情况。铝制锅所做的酱料颜色看起来会更灰些，吃起来也不如其他厨具所做的酱料味道好。