At 09:38 AM 3/9/2010, Chris S wrote: >Are you saying that the temperature of water ice which comes out of a >0F freezer is 32F? Methinks not. No, it's zero; but it rapidly rises by absorbing energy at the rate of one calorie (1/1000 of the Calorie or kilocalorie that dieters work with) per degree C until it reaches 0C/32F; at that point temp remains constant while it absorbs an additional 85 (?) calories per gram to change into liquid water still at 0C/32F. Therefor water ice cannot effectively cool below 32F and has trouble reaching that. Adding rock salt (or many other things) to the melting ice lowers the melting point by an amount proportional to the amount of solute (salt), and the ice begins melting (and absorbing its 85 calories per gram) at a lower temp than 0C; with rock salt this trick can get the overall temp down to 0F in ideal conditions. 15F or so would be about right for soft ice cream coming from the churn as colder than that makes it too stiff to churn. Normally then more salt would be added and the mixture cooled for a couple hours as close to 0F as possible to make hard-ish ice cream. Ice cream actually at 0F or below is usually quite hard. Calcium chloride (fancy ice melt) would be ideal for this except that the act of dissolution generates large amounts of heat -- you can easily get 180F by making a concentrated solution. Yours, David |
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