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# Cookery and Culinary Arts/Steaming at low temperature

Question
Dear Mr. Price,

In many sources it is recommended to steam food at 70 degrees Celsius or lower in order to preserve the food's nutritional benefits as much as possible. As I understand, when the water for steaming is boiled, the water is 100 degrees, and the resulting steam is also 100 degrees.
How is it possible to steam food at a temperature of 70 degrees or lower?

With many thanks in advance for your help and many greetings from France,
Aaron

Aaron, bonjour from the States - that's a great question!

Your assumption about the temperature of steam is mostly correct.  Water turns into steam at 100 C (212 F) and steam condenses back to water at 100 C at standard pressure.  Steam can exist at temperatures greater than 100 C, but for all practical purposes, outside of a pressure cooker, any steam you deal with in the kitchen will be just about 100 C.

It is possible to steam something at 70 degrees C(158 F for us yankees), but I can almost guarantee you that nobody does it.  At standard atmospheric pressure, water boils, and therefore produces steam, at 100 C (212 F).  If you increase the pressure, say in a pressure cooker, you increase the temperature that the water needs to boil.  Add an extra 70 KPA (10 PSI) and your water won't boil until 115 C (240 F).  That and some great heat transfer properties of steam are the reason pressure cookers work so fast compared to traditional methods.

The inverse is also true, reduce atmospheric pressure and the boiling point of a liquid drops.  In a vacuum, water boils quite readily at room temperature.  If you were able to lower the pressure say, 100 - 120 KPA or so, your water would boil, and therefore create vapor, at 70 F.  I can't imagine doing anything like this outside of the laboratory, but if you did manage it, the water would cook slowly and never cook anything above 70C (158F).

That's not to say you can't have a 70C moist environment in which to cook food.  If you put a pot of water on the stove at a low enough temperature that the water is hot but not boiling, then close the lid, you could potentially cook something in the enclosed air.  It wouldn't really be steaming though - a small portion of the heat transfer would come from steam but most would come from conduction through contact through the air with the sides of the pan and the water.

I think I should also point out that cooking at a lower temperature isn't really that big of a factor in nutrient retention.  The fact that the food is steamed instead of submerged in water is the biggest concern by a huge factor.  The length of cooking time is also far more important in nutrient retention than is cooking temperature, at least when we're talking temperatures below the maillard point (154 C or 309 F).  Low temperatures often have huge positive impacts on the texture and flavor of food though, so there's definitely a place for it.  Really it's another tool in your culinary arsenal, and a versatile one if employed properly.

Good luck!
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Thank you, very much, Adam, this was a truly great answer, exploring the issue thoroughly, in detail, and with clarity. I really appreciate that. Thanks again!

Cookery and Culinary Arts

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