Tempering chocolate: ± 2 °C too much?

Question

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!

Asked by Sven

Answer

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.

Answered by rumtscho

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Thermometer Precision in Different Temperature Ranges

Question

I need a thermometer for a variety of different applications. As such, it has to be fairly precise (plus/minus 2 degrees) at different temperatures. Do I have to worry that, if I buy a thermometer which has a large range (0 to 300 C, for example), that it won't be sensitive to small changes in temperature near 40 C?

Answer

There are several type of thermometer. Since you didn't specify exactly what you will be using for the thermometer It's hard to tell which type you are getting. However the two most likely kind you will use are bulb thermometer and bimetal thermometer.

The way bulb thermometer works is there is a liquid inside of a thin tube. Heat expands the liquid so the higher the heat the more it expands. The liquid is calibrated to expand to the markings on the thermometer.

However, the sensitivity of a thermometer does not depend on it's range but rather on several different factors:

• The size of the bulb on the thermometer. If the bulb is smaller it absorbs heat faster thus expanding to the appropriate notch on the thermometer faster.
• If the walls of the thermometer is thinner, it will also result in the heat being absorbed faster.

A bimetal thermometer operates on the principle that different metals contract and expand to different degrees when exposed to temperature changes. Two strips made of different metallic materials are fused together as a spiral or rod. The strip will wind, unwind or bend as the temperature changes because one of the two materials in the strip will contract or expand to a greater degree than the other will. The free end of the strip is attached to a pointer that will indicate the temperature.

Once again because the dial moves base on the expansion (this time metal) which will stay constant, the range of the thermometer will not be affected.

Please note that over time these metal might degrade and lower the sensitivity of the thermometer but that is an issue of the longevity of the equipment.

Also note that is it harder to read the smaller changes by the human eyes if the range is larger since is scale is smaller but that has nothing to do with it's sensitivity.

EDIT:

If by chance you are refering to the uncertainty of a thermometer or how "incorrect" a thermometer can be, as Rumtscho mentioned, the uncertainty is usually given in the specs of the thermometer and you will need to do some research to find the one that will fit your needs. Just for example Tel-Tru boast an uncertainty of just +/- 1/10th degree Fahrenheit for it's products. You can usually find this sort of information on the product's website.

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What are the differences between candy thermometers and meat thermometers?

Question

I know that meat thermometers generally won't handle as high a temperature range as candy, but I'm only planning to make caramels and fudge (so soft ball and firm ball) and that's within the range of the meat thermometer that I already own.

Also, meat thermometers are often labelled "medium well" etc., rather than "soft ball". Since I have access to the temps required, that's not an issue.

I'm definitely a noob to candy, so is there some magical reason I can't use a meat thermometer for my candy? Is it a huge no-no? Does it contain leprechauns that will destroy my caramels?

Answer

I think Doug and yossarian both touched on the main points, but to summarize, there are four reasons why you might not want to use a meat thermometer for candy:

1. Range A meat thermometer might go from 140 F to 220 F or something like that, which is plenty for meat. Candy often requires a range from about 75 degrees (chocolate) up to 400+ degrees (hard candy). The range on most thermometers is simply not sufficient for most candies.
2. Accuracy When you temper chocolate, 88 F degrees is an ideal working temperature (for dark chocolate). Some people would consider 91 so high you might want to think about starting over. When you make caramels, the difference between 235 F and 240 F can be the difference between wonderfully chewy caramels and a sugar-flavored rock. If you can't read one degree increments at a glance, you need a real candy thermometer.
3. Speed Meat thermometers often take 30 seconds to a minute to get an accurate result. When you are making candies, you have to be able to tell what the temperature is right now.
4. Contamination I don't want the thermometer that goes in semi-raw meat anywhere near my chocolate.

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