When you boil potatoes on the stove top, it can take half an hour to cook them ’til tender. But, when you boil them in a pressure cooker, instead presto, they’re ready in about five minutes. What’s the difference? What makes pressure cookers cook so quickly?

 

　　Let’s start with the potatoes boiling on the stove top. The temperature of the boiling water won’t go above 212 degrees Fahrenheit, no matter how high you turn up the burner or how long you leave the pot on the stove. That’s because, at normal air pressure, water boils at 212 degrees and escapes as steam.

 

　　In a pressure cooker, on the other hand, the steam can’t make such an easy getaway. The sealed lid keeps the steam inside, raising the pressure inside the cooker to about twice normal air pressure.

 

　　Now here’s the secret of speedy pressure cooking. As pressure rises, so does the boiling point of water. At the higher pressure inside the cooker, the boiling point of water goes up to about 252 degrees. So, food cooks at a much higher temperature in a pressure cooker, and that`s why it cooks more quickly.

 

　　Pressure cookers control cooking temperature by maintaining a certain pressure. A vent on the lid releases steam when the right pressure, and therefore the right cooking temperature is reached. And to prevent disasters like boiled potatoes exploding onto the ceiling, modern pressure cookers also have a safety valve to release steam, just in case the vent gets stuck.

 

　　高压烹饪

 

　　如果将土豆放在炉子上烹煮，需要半小时才能煮熟。如果将土豆放入高压锅，只需短短5分钟就熟了。两者有何区别呢？为何高压锅烹饪如此迅速？

 

　　让我们从炉子上煮的土豆开始说起，无论你将煤气灶调至多大，抑或是烹饪时间多长，水的沸点都不会超过华氏212度。这是由于在标准大气压下，水达到华氏212度就会沸腾并形成水蒸气挥发掉。

 

　　而对于高压锅而言，水蒸气并不会如此容易挥发出去。密封盖将水蒸气封存在锅里，锅内压强升至标准大气压的两倍。

 

　　现在让我们解开高压锅快速烹饪的秘诀。随着锅内压强上升，水的沸点也逐渐升高。锅内压维持在较高水平，水的沸点上升至华氏252度左右。因此，在高压锅中烹饪食物的温度更高，烹饪时间明显缩短。

 

　　高压锅通过维持某一压力来调节烹饪温度。密封盖上的排气孔释放水蒸气，以此达到合适的压力，烹饪温度也随之到达理想值。为了避免发生诸如煮熟的土豆炸飞到天花板的意外情况，现代高压锅还有一个安全阀门释放水蒸气，以防排气孔堵塞。