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Which thermometer? It makes a big difference.

Which thermometer? It makes a big difference Correct temperature is critical to success in cooking. And whether you're aiming for a medium-rare roast, creamy fudge, or golden doughnuts, a reliable thermometer can help you judge the best conditions for cooking and when the food is done.

Walk into any store that carries cookware and you'll find thermometers of seemingly every description. There are ones for different categories of food, for regular or microwave cooking, for instant or conventional readings. Which suits your needs?

First, it helps to realize there are two basic types currently on the market: bimetal and glass column. (A third type--the digital probe--is expected on store shelves in the near future.) Within each category, different models are intended for certain uses, from double-checking oven temperature to tempering chocolate.

Here we give a complete rundown to help you select the right thermometer--and, on page 188, tips for getting the best results, based on our own experiences.

Bimetal: slow to fast

You can recognize bimetal thermometers by their dial face. The pointer in the dial connects to a spring made of two metals sandwiched together. When the temperature changes, each metal expands or contracts at a different rate, causing the spring to wind or unwind. Because of slight inconsistencies in the expansion or contraction rate, bimetal thermometers are best for uses where accuracy to the precise degree isn't necessary.

One asset is that the dials are generally easy to read; some are especially large, have magnifying covers, or come with adjustable red arrows on the rim to use as temperature locators.

Stand-mounted oven thermometers have a coil spring that reacts slowly to temperature changes so that briefly opening the oven door won't affect the reading. Stem-mounted food probes are faster, but their movement may be slightly jerky.

Instant-read thermometers, another bimetal type, have the dial mounted on a more slender stem that holds a faster-reacting spring. Most can't be left in the oven while food cooks (some models have parts that may melt), but their slim stem and quick response allow frequent use to check progress.

Most bimetal styles cost $3 to $7; instant-read models range from $10 to $15. All are relatively durable.

Glass: accurate but fragile

A thin glass tube holds colored liquid (usually nontoxic alcohol for food use), which expands up the tube as it heats. A scale alonside records temperature. Choose this style when accuracy and consistency are important. If the thermometer is placed in the food or oven as it heats, it can respond almost instantly.

Although some have a protective stainless steel shaft or sheath, the glass tube is fragile. If you heat the thermometer past its range, its top can blow off. If one is dropped, the liquid may get separated by an air bubble, making the readings inaccurate. Sometimes you can fix this by gently tapping the end on a flat surface.

Look for a thermometer that is securely attached to its scale. If it comes loose from its moorings, it is hard to reposition.

Because you need to read glass thermometers straight on to see the colored liquid, they are more difficult to read than most dial models. Cost is $8 to $10.

Digital probes: style of the future?

Already used in the food industry, digital thermometers with metal-resistance or thermocouple sensors provide very accurate, almost instantaneous readings. Several models for home-kitchen use are under development now. Some units may be built into ovens; others will be portable. Since temperature ranges will vary, watch for ones that suit your purposes.

Which thermometer for what use?

Keep this trade-off in mind: thermometers with wider temperature ranges are more versatile, but those with narrower ranges are more accurate and easier to read. Also, on long scales, accuracy is greatest towards the middle of the range.

Our chart covers the three basic categories: oven, candy or deep-frying, and meat thermometers. In addition, you may want to consider the following models.

Grill thermometers, designed to use in barbecues, have a range up to 600 [deg.]. Special candy thermometers useful when tempering chocolate start around 80 [deg.]. Floating models for monitoring fermentation of yogurt, beer, or wine range from 20 [deg.] to 200 [deg.]. For making cheese, you can use a glass body-temperature thermometer, since the short range is suitable.

Instant-read thermometers, designed for multiple uses, have widely varying ranges; choose one that suits your needs. Microwave thermometers are all-purpose models; since materials vary, check your oven's instructions about suitable types.

With any thermometer, expect price to reflect quality. Check for tight (perhaps dishwasher-safe) construction, sturdy housing, and clearly marked increments.

Double-checking your oven temperature

Many ovens run hotter or cooler than their setting. To check, put the thermometer in the oven where you intend to cook the food, generally in the middle. Preheat the oven; when it reaches the preset temperature, read the thermometer (allow 3 to 5 minutes for bimetal ones to stabilize).

If possible, read the temperature through a window in the door; otherwise, open the door for a qucik read. Compare this temperature with the oven setting. If there is a difference, adjust the oven dial accordingly. Let the oven adjust to the new setting, then recheck the thermometer; it should be close to accurate. You can leave the thermometer in the oven, but it will fluctuate as the oven cycles on and off.

Oven thermometers can also be used in covered barbecues over indirect heat. Do not set one directly over the coals; it may get too hot and break.

Test for accuracy

A thermometer is only as good as it is accurate. You can test most styles to verify their readings.

High altitudes and barometric pressure change the boiling point of water. If water at your altitude boils at 205[deg.] instead of 212[deg.], you'll need to subtract 7[deg.] from the temperature called for in recipes.

With thermometers that stop below the boiling point, check them against a laboratory one certified to a resolution of plus or minus 1[deg.]. Science equipment stores sell them for $5 to $10.

Immerse the end (follow manufacturer's recommendations for depth, usually 2 to 3 inches) of the lab and testing thermometers (fully immerse glass oven styles) in the same container of water at the temperature range you want to check. Allow the thermometers a few minutes to stabilize, than compare temperatures. If there is a difference, allow for that when using that particular thermometer.

Some bimetal meat thermometers whose range ends below boiling have a test zone to use in boiling water; if the pointer falls within this zone with the stem immersed in boiling water, it is fairly accurate.

Bimetal oven thermometers are difficult to test at home. The best way is to place them in the oven with another thermometer you know to be accurate.

Meat rare or well done?

Insert the thermometer so its end rests in the area you want to test for doneness. Most roasting charts are based on the internal temperature of the meat in the thickest part, usually the center in a boneless roast. In a bone-in roast, it is commonly suggested to place the thermometer tip in the thickest part without touching bone or fat.

Contrary to most authorities, we find that bone does not seem to conduct heat; rather, a bone through the center of the roast is the last area to cook. If you prefer meat done to the bone, check the temperature at the bone in the thickest part. If you prefer most of the roast to be rare, place the thermometer tip in the thickest part between the bone and surface.

Use doneness charts only as rough guidelines; your experience matched with your own preference are better ways to judge.

From a safety standpoint, meat does not need to cook as long as you might think or as some thermometers indicate. Trichinosis in pork is destroyed when the temperature reaches 137[deg.] and stays there for at least 1 minute; staphylococcus and salmonella are killed at 140[deg.]. Pork is white throughout and much juicier at 150[deg.] to 155[deg.] than at the currently accepted 170[deg.].

If you prefer meat done at a lower temperature, such as very rare beef at 120[deg.], choose cuts that require minimum handling, such as whole muscles or bone-in roasts. To prevent the growth of undesirable bacteria or toxins, store it well chilled.

Many manufacturers and cooks recommend you remove the roast from the oven 5[deg.] to 15[deg.] below the preferred finished temperature, suggesting the meat continues to cook after it comes out of the oven. We suggest you cook the meat until the thermometer reaches the desired doneness, then let it rest before serving.

In our many years of testing, we have seldom found the internal temperature to rise significantly outside the oven. In fact, with thermometers (especially glass) left in the roast during the entire cooking time, the change to cool air outside the oven often causes the temperature to fall several degrees, then stabilize. Because instant-read thermometers aren't subjected to the air temperature change, they are good for rechecking the internal temperature; give them a minute or so to stabilize.

After the roast rests 10 to 20 minutes, instead of a temperature increase we often see a change in the interior meat's texture and color as residual heat and meat juices redistribute themselves. Meats seem more evenly cooked; even rare soft interiors firm up slightly but stay pink.

Candy making: a matter of degrees

Glass thermometers provide the most consistent and accurate readings for candy making and can be used with smaller quantities of liquid than bimetal ones can.

Insert the thermometer so the bottom of the glass tube clears the pan bottom and the liquid covers the base of the tube by the depth recommended by the manufacturer, usually about 1/2 inch. Some models are mounted on a metal shaft that will keep it off the pan bottom; a clip holds it along the pan sides. With this type of thermometer in place, you can continually monitor the mixture's progress. Small increments of 2[deg.] to 5[deg.' are easier to read.

Clip bimetal thermometers to the side of the pan so the tip clears the pan bottom and the stem is immersed in liquid by at least 2 to 2-1/2 inches or to the manufacturer's recommended depth; you may need to tilt the pot to achieve this.

Deep-frying: consistently crisp

If the oil is too cool, results will be limp, pale, and soggy. If it's too hot, the exterior will brown before the interior is done. A bimetal, instant-read, or glass column registering 325[deg.] to 400[deg.] is adequate.

Immerse a glass or bimetal thermometer in the oil by at least the depth recommended by the manufacturer, usually 1/2 inch for glass, 2 to 3 inches for bimetal. Clip it to the pan side so its base clears the bottom. Or immerse an instant-read thermometer in oil periodically. After each batch, let the oil return to the correct temperature before adding more food.
COPYRIGHT 1986 Sunset Publishing Corp.
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Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Date:Nov 1, 1986
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