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I am planning to buy a laser thermometer to measure the temperature of melted chocolate for tempering it. As I have found out, the thermometer I want to buy has a measuring tolerance of ± 2 °C. That means even if it shows the correct temperature on the display, the chocolate can be 2 °C too hot or 2 °C too cold. Will this cause any trouble? Do I really need a thermometer that has a smaller measuring tolerance?

FYI: 2 °C are about 36 °F

Edit: 2 °C are about 3.6 °F, thanks msh210!

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up vote 3 down vote accepted

Yes, it is too much. Chocolate has very tight working intervals. Dark chocolate must be used at 32°C. Below 30°C, it is too thick for use, and at 35°C, the cocoa butter separates from the chocolate. An error interval of 4°C when your complete workable interval is 5°C wide is simply unacceptable. You want a thermometer with a much higher precision, actually one which shows you tenths of degrees centigrade.

You also want a thermometer which reacts quickly enough. If you are working with small quantities, a ten seconds delay in measuring can give you errors of over half a degree centigrade, which is also a lot, given your tight working interval. Try finding a thermometer with a 4 sec response time or less.

Also, you don't want a laser thermometer at all! The difference in temperature between the surface of the chocolate and the mass of it near the bottom can be substantial, I once measured 4°C difference in something in a bowl with about a litter of stuff (it can't have been chocolate, probably it was custard, I forgot exactly). You need a candy thermometer for chocolate. Buy a laser thermometer separately for measuring the surfaces of pans, if you need it.

As a last note a 2°C interval is not 36°F, it is just below 4°F. The formula is 32 + 5/9, so your converter probably meant that when there are 2°C outside, a Fahrenheit thermometer shows 36°F. This is obviously incorrect for calculating intervals.

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Wow! Thank you for that answer! –  Sven May 25 '12 at 10:11
    
But classical sugar thermometers might be a bit too slow? I have that problem with mine at least. –  daramarak May 25 '12 at 14:16
    
@daramarak, a classical sugar thermometer is meant to be immersed in whatever you're cooking at the beginning, and stay there throughout. Thus, it comes up to temperature at the same time as your candy, so there's really no delay between a temperature being reached and the thermometer saying so. –  Marti May 25 '12 at 17:22
    
A digital probe thermometer is a viable alternative. Get a decent one with a quick response time. It's useful in all kinds of cooking, not just chocolate/candy –  ElendilTheTall May 25 '12 at 20:17
    
I have always been afraid that the temperature in the bottom of the pan might get too hot. After all I want the temperature of the mix and not the pan. So this isn't a concern? –  daramarak May 25 '12 at 20:25
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