Sunday, October 02, 2005
Cajeta Cocinada a Presion
A new look at cooking of Dulce de Leche:
Standard Crock-pot method:
Peel off label. Place can in crock-pot an cover completely with hot tap water. Turn crock-pot on high and cook for 3-4 hours making sure can stays completely submerged. Remove can and cool completely before opening. http://hobey.blogspot.com/2005/09/ooey-gooey-goodness.html
New Pressure Cooking Method:
Pressure cooking speeds up the rate of reaction. Using the Arrhenius Equation,
Time(new) = Time(old)/eb(1/T(old, in K) – 1/T(new, in K))
We can determine how much we can shorten the cooking time by raising the temperature.
A typical “b” value in the Arrhenius equation for cooking processes is 10,000 K.
°C = (210– 32)*(5/9) = 98.8
K = 98.8 + 273.15 = 372.4
°C = (250– 32)*(5/9) = 121.1
K = 121.1 + 273.15 = 394.3
Time(new) = 240 min (or 180 min) /e10,000(1/372.4 – 1/394.3)
Time(new) = 54 min. corresponds to 4 hr. cook; 40 min. corresponds to 3 hr. cook.
Cooking time for first trial will be 60 minutes at 250 degrees F, 15 psi steam.
A quick calculation of the pressure inside the can, shows the air pressure will be about 5.5 psi over atmospheric at 250 degrees. I am unsure of the vapor pressure of the milk slurry, but it will be lower than the 15 psi of water. The max pressure over steam pressure then will be 5.5 psi.
Fred starting the pressure cooker.
Looks good,
Final product is delicious. The next batch I plan to reduce the cooking time to 40 minutes.
Standard Crock-pot method:
Peel off label. Place can in crock-pot an cover completely with hot tap water. Turn crock-pot on high and cook for 3-4 hours making sure can stays completely submerged. Remove can and cool completely before opening. http://hobey.blogspot.com/2005/09/ooey-gooey-goodness.html
New Pressure Cooking Method:
Pressure cooking speeds up the rate of reaction. Using the Arrhenius Equation,
Time(new) = Time(old)/eb(1/T(old, in K) – 1/T(new, in K))
We can determine how much we can shorten the cooking time by raising the temperature.
A typical “b” value in the Arrhenius equation for cooking processes is 10,000 K.
°C = (210– 32)*(5/9) = 98.8
K = 98.8 + 273.15 = 372.4
°C = (250– 32)*(5/9) = 121.1
K = 121.1 + 273.15 = 394.3
Time(new) = 240 min (or 180 min) /e10,000(1/372.4 – 1/394.3)
Time(new) = 54 min. corresponds to 4 hr. cook; 40 min. corresponds to 3 hr. cook.
Cooking time for first trial will be 60 minutes at 250 degrees F, 15 psi steam.
A quick calculation of the pressure inside the can, shows the air pressure will be about 5.5 psi over atmospheric at 250 degrees. I am unsure of the vapor pressure of the milk slurry, but it will be lower than the 15 psi of water. The max pressure over steam pressure then will be 5.5 psi.
Fred starting the pressure cooker.
Can upon removal from pressure cooker, notice slight bludge of can top.
Isn’t science exciting?
Looks good,
Final product is delicious. The next batch I plan to reduce the cooking time to 40 minutes.
# posted by Fred @ 6:38 PM 
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Rolling on the floor here. :) This is great! I don't know if I'll be brave anough for that one but I'm definitely intrigued.
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