On 13/06/2012 3:55 PM, dsi1 wrote:
> On 6/12/2012 9:56 AM, spamtrap1888 wrote:
>>
>> I know what you mean. I cooked a beef roast at 325F the other day. Did
>> you know it took well over an hour for the roast's internal
>> temperature to reach 140F? What gives?
>>
>> I think the answer in both cases is that pressure cookers transfer
>> heat mostly via steam, while ovens transfer heat mostly via air.
>>
>
> I think you're right about this. Steaming is an interesting process.
> When the steam hits the cooler food, it condenses on the surface and the
> latent heat of the steam is released. It's the opposite of sweating
> where the sweat changing into a gas absorbs heat. The energy it absorbs
> will again be released when it either turns back into a gas or when it
> freezes.
>
>

I think you maybe wrong about that. You need a physics lesson. Water
changes to a gas vapour at 212F at sea level and at a lower temperature
at higher altitudes, so when you are cooking at sea level you water is
only going to heat up to 212F, though adding salt will raise the boiling
point a bit. Cooking under pressure allows the temperature to get up to
about 250 degrees, and the steam pressure is forced through the food.