Tuesday, August 18, 2009

Why Use a Thermometer?

If you're like me and most of the population of America, I'm sure you've heard the following phrases uttered by everyone from your Grandma to authorities on cooking like Julia Child herself (God bless her):
  • Bake at 350 degrees until the juices run clear when a knife is inserted into the thigh.
  • Bake at 350 degrees for 15 minutes per pound. Actual time may vary.
  • Bake at 350 degrees until a toothpick inserted into the center comes out clean with a few crumbs sticking to it.
  • Roast chicken until the leg joint moves easily when you "shake its hand"
  • A steak is medium-rare when you push on it and it feels like the part of skin between your thumb and forefinger while your fingers are relaxed.
  • Etc., Etc.
There are some crazy ways of determining when things are done cooking. Some are more reliable than others. Some are just plain crap. The toothpick test, for example, works reasonably well for cakes and quick breads. You won't undercook it, but you may overcook it (I'll explain in a moment).

As for the fuzzier ones like shaking the chicken's hand or comparing your steak to the flesh of your own hand, they're a little less reliable. The steak trick works...if you're a professional chef cooks steaks day in and day out. The handshaking chicken deal works...if you want your chicken cooked till the breast is sawdust.

So how *do* you know? You know? The simple answer is to use a thermometer. You'd be surprised how many kitchens don't have one of these simple and inexpensive tools. I never had one myself until I started taking cooking seriously and it's improved the quality of the food I cook immensely by eliminating a lot of the guess work. The trick is understanding exactly how different temperatures affect the foods you cook so you can judge the temperature you should be looking for. But before I get into that, let's talk about choosing a thermometer.

Choosing a Thermometer
First and foremost, you don't want the one Grandma used to leave in the thanksgiving turkey while it was in the oven. While those are handy for specific tasks, what you really want is an "instant read" thermometer. Those do exactly what you'd expect. They instantly read the temperature of the food you plunge them into and they'll melt if you try to put them in the oven with the turkey. Trust me. I did it by mistake one day. :-)

If you're a psychotic cook like me, you've probably already gone out and plunked down the $89 for a Thermapen digital instant-read thermometer like the chefs use on TV (okay, mine was a Christmas gift). It's the Cadillac of thermometers, is uber-accurate, and continues to win the praises of reviewers like Cook's Illustrated magazine. However, you don't need an $89 thermometer to be a good cook. In fact, I wouldn't spend more than twenty bucks on one unless someone else is buying.

One of the most basic, most reliable models out there is the simple analog pen-style thermometer. These are the ones you see hanging out of most chefs' pockets and they're also the ones you see Starbucks using to heat milk to just the right temperature for that non-fat, sugar-free, grande mocha latte. It doesn't need batteries and the probe end has less of a chance of malfunctioning over time because of how it's made. Just make sure you buy one where you can clearly read the numbers and that can be calibrated by turning a small nut just underneath the dial. To calibrate it, plunge the tip into a glass of water filled with ice and make sure it reads just under 212 degrees (the freezing point of water). If it doesn't, turn the nut and re-test until it's right. A word of caution about the models that have the words "poultry, roast beef, etc." right on the dial. They technically work, but if you want something other than well-done, forget it. Choose the model with the numbers and get yourself a good chart instead.

If you must have a digital model, CDN makes one for under $20 that was rated as accurate as the Thermapen by Cook's Illustrated magazine, but it responds a few seconds slower. I've never used it, but I generally trust the folks at Cook's. In fact, I know their equipment editor personally and she's dang good at her job. I also know they use the CDN model in their test kitchen to keep replacement costs down.

How Does it Work?
There's a lot of food science that goes into cooking. However, what you need to know to use a thermometer is very simple. When you cook something, you're heating it (duh). As it heats, the molecules in the food change, creating new flavors and textures that we associate with cooked food. Water also moves around, sometime exiting the food into the pan and then turning into steam and sometimes moving to the surface of the food. This can be good or bad, depending on what you're looking for.

It's difficult to know when a food has achieved the particular flavor compounds you're looking for or how much moisture is left in it based on cooking time time and the temperature of the oven or stove as these indicators are quite inconsistent. However, most of the characteristics we're looking for when we cook food can be consistently tied to the internal temperature of the food at any given point. If we get to know these target temperatures, we can, in theory, produce consistently cooked, flavorful food with just the right moisture content...every time.

Testing Meat & Poultry
One of the more obvious things you can use your thermometer to test is meat and poultry. When testing, plunge the thermometer probe into the center of the thickest part of the meat. For larger cuts or roasts, test in 2-3 places. Remember that the very tip of the thermometer is what's doing the work, so take care not to take the temperature of the pan or the air instead of the meat.

Here are some guidelines and explanations of what you're looking for for each kind of meat:
  • Steak - When it comes to cooking steak, temperature is the only guaranteed way to arrive at your favorite doneness (rare, medium rare, medium, medium well, and well done). Get yourself a reliable chart, like this one on Wikipedia, print it out, and keep it in the kitchen. I find holding the steak firmly with a good set of tongs and plunging the probe into it sideways works best.
  • Beef Roasts - Beef is beef, so you can use the same chart listed above for temperatures. Make sure to test in 2 to 3 places. Keep in mind that roasts are usually unevenly shaped, so one end of the roast may be medium while the other end is well-done. A good cook will use this to his advantage to satisfy the differing preferences of his guests rather than assuming everyone should like their meat medium-rare. Also remember that there will be 5-10 degrees of carry-over cooking once you remove the roast from the oven, so stop 5-10 degrees early.
  • Pork - Pork chops and pork roasts work similar to beef and steaks. However, you'll often find that cookbooks recommend that you cook all pork to 190 or some aweful temperature that renders it into sawdust. As mentioned before, pork is quite clean today and you can eat it safely at much lower temperatures. My rule of thumb is to make sure it's at least 140. At 140, lean pork will be a little pink in the middle (medium), still soft, and quite juicy. If you're like me and you like it cooked through, 150-160 should be your target. Anything over 165-170 will likely be on the dry side.
  • Whole Birds - Whole birds like turkeys and chickens are tough because light meat and dark meat cooks at different rates and the bird itself is unevenly shaped. Chicken should always be cooked through, so try to get 160-170 in the breast meat and 150-ish in the legs and thighs. If you find that the breasts are cooking way too fast, cover the bird with tin-foil to deflect some of the heat and help steam the legs a bit.
  • Lean Poultry - Lean poultry such as boneless skinless breasts or tenders are the easiest to overcook because they're lean and unevenly shaped. Again, I shoot for 160-165. Another trick is to make sure the thickness is even, either by butterfly-cutting thick breasts or pounding with a meat mallot. There's very little carry-over cooking with these cuts.

Baked Goods
I'll bet you've never seen a pastry chef with an instant-read thermometer peeking out of his pocket. I'm not at all sure why since the internal temperature of a loaf of quick bread or bread tells us a lot about how much moisture is still in there and, effectively, how dry our baked good will end-up. How does this work?

We all know that the boiling point of water is 212 degrees. At this point, water begins to turn to steam and dissipates into the air. Baked goods, especially yeast breads, are pretty much at their peak at this point because they're done cooking and there's still enough water in them to be moist. Go any higher in temperature and all the water has evaporated, meaning your baked goods will be dry and hard.

When taking the temperature of a baked good, test it in an inconspicuous place so you don't leave a gaping hole in it. If you can turn the bread over without burning yourself, the bottom is a good place.

Reheating Food
I was at someone's home one day for a family gathering and they were reheating a pan of lasagne. Knowing I like to cook, the person asked me, "Do you think it's heated-through?" to which I replied, dumbly, "I dunno. I usually just stick my finger in it to find out."

Needless to say, my mind immediately began asking itself how one would properly determine if a pan of lasagne is hot without jamming an appendage into it, possibly getting burnt, ruining the visual aesthetics of the dish, and grossing-out those present who don't know where your finger has been. The answer, of course, is a thermometer. But what temperature? To figure this out, let's work it out using what we do know about food science and the serving temperatures of other foods we eat.

First, temperatures below 140 degrees are what we call "the danger zone." We call it that because most harmful bacteria can grow below that temperature but will die at temperatures above it. In fact, pasteurized milk is nothing more than milk that's been heated beyond 140 and then sealed into the sterilized container. That said, we want our food to be above 140 to make sure it's safe.

The second bit of of useful info is that the milk for a latte is generally heated around 150 to 165 degrees and coffee and tea are brewed at 180 to 200 degrees. I dunno about you, but I don't want lasagne, or anything for that matter, to burn the roof of my mouth and that's what freshly brewed coffee or tea is capable of. So, I'm sticking well below 180.

The third bit of info that will narrow it down further is that perfectly done chicken is about 165 when it comes out of the pan. I can generally eat it when it is served, so let's assume 160-ish is a good serving temperature. And that, is what I'd use for reheating food.

Here's something kind of geeky and cool. Some older microwaves came with built-in probe thermometers. If yours has what looks like a headphone jack on the roof of the cavity, start digging in the junk drawer for a thermometer probe with a wire and the corresponding jack on the end of it. If you can find your user manual or just tinker around for a bit, you'll find that you can tell the microwave to cook something at a certain power until the temperature reaches a particular level and then stop, measured by the probe. Pretty neat, huh?

And that leads me to the last thing...

Digital Remote Probe Thermometers
Probe thermometers are designed to be left in a piece of meat while it's in the oven rather than having to take it out and check it every few minutes with an instant-read. They're great when they work and the digital ones are even better because you can read the temp without opening the oven door (and not letting the heat out) and you can set it to notify you via an alarm when the target temp is reached. They even make ones with a transmitter and a receiver that you can clip on your belt so you can hear it in the next room (or in the house if you're measuring something on the BBQ).

Unfortunately, modern digital probe thermometers seem to have rampant problems with the probes. Sometimes, you buy one and the probe is dead or way off calibration. The companies generally will send you a new one if contacted but sometimes the replacements aren't much better. I have one and I love mine when it works. My only recommendations are: Don't pay too much for one...$30-40 is plenty; use it to get yourself into the target zone and then begin testing with an accurate instant-read. Eventually, you'll have an idea how off it is and will be able to compensate.

No comments:

Post a Comment

I welcome comments. However, please be courteous of others when commenting. I always reserve the right to delete inappropriate comments.