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Monday, March 5, 2012

Sous Vide Cooking

A few weeks ago, my mom sent me a link to an article on sous vide cooking. Sous vide was a technique of which I was aware, having seen it used on Iron Chef America, for instance, but I never really paid it much attention. After reading the article, I became more curious and started doing a little research. Fascinating stuff!

If you're not familiar with the basic idea, sous vide means "under vacuum" in French. While generally the food is vacuum sealed to cook, the really significant part of this method is that it cooks the food in a water bath, very slowly and gently.

The most surprising thing I learned is that all this time, what I thought I knew about food safety and safe cooking temperatures was not quite accurate. What I didn't realize is that when you read one of those charts that dictates what minimum temperature to cook various meats, you are only getting half of the story. Apparently, the USDA/FDA doesn't have a lot of faith in the masses. Those temperatures? Those are the required temperatures for "instantaneous" safety. The government, for instance, recommends you cook poultry to an internal temperature of 165 degrees. However, you can safely cook food to much lower temperatures provided you lengthen the time it is at this temperature. This graph shows the relationship between cooking temperature and time required for safe consumption. Notice that the longer the food, in this case beef, is held at a specific temperature, the lower the maximum temperature can be for safe consumption. For instance, at 140 degrees, you must cook the meat for 10 minutes while at 135 degrees, you must cook the meat for almost 35.

Now, why does this matter? Well, consider chicken breasts. This meat can suffer from problems with dryness if cooked to the USDA/FDA recommended "instantaneous" safe temperature. I don't know about you, but I don't particularly care for eating dry, tough, stringy pork chops or chicken breasts. Sous vide allows you to cook these meats at a much lower temperature, leaving those juicy flavors and textures intact, safely. If you go looking for your own sous vide information, I would advise you that in many cases, the recipes you see online do not guarantee pasteurization of the food. While I do not mind eating under cooked foods in some cases (sushi grade fish or very fresh beef, for instance), I personally don't want to consume chicken that has not been heated to the point of safety from a pathogen stand point. Therefore, if you are concerned about food safety, always look for guidelines that stipulate the food will be pasteurized at the times and temperatures given.

The best resource that I found for sous vide is put together by a mathematician named Douglas Baldwin at the University of Colorado. He has a lot of useful information on his website, but the most important, I think, are his tables of cooking times. Mr. Baldwin has taken all of the guess work out of how long to cook the food for pasteurization. Without these tables, it can be very difficult to be sure your food has been held at the right temperature for the right amount of time. He calculated the times using the thermal characteristics of the water and of the various types of meat. A few things to take note of: the thickness of the meat affects cooking time and so does the amount of fat in the meat. Thickness and time is not a one to one relationship. If you double the thickness of the meat, you must quadruple the cooking time. More fat equals more time required for pasteurization.

Using the tables is easy! Below, for example, is his Table 4.1 showing the pasteurization times for poultry. I realize the type is small in this picture... you can click on the link to the table to view in full size on his site if you'd prefer. Notice that he gives a range of temperatures. He provides the times required for pasteurization to any of these various temperatures. The trick is, which one to pick? It is purely a personal preference. The lower the temperature, the closer to raw color and texture you will end up with; the higher the temperature, the closer to fully cooked color and texture. The opening photo of this post shows a chicken tenderloin that was cooked at 142° F. Notice how juicy and still slightly pink it is? It is perfectly safe to eat, because I held it at 142 for the required amount of time, but it was so juicy and succulent! That's the joy of sous vide!

So how long did I cook it? Well, my chicken was about 15 mm thick, so once my water reached 142 degrees, I placed my vacuum-sealed chicken, which had been marinating in the refrigerator, in to the water bath. I then cooked, holding the temperature steady at 142, for 50 minutes. Pasteurization requires holding the meat at the specific temperature once it has reached that temperature throughout. His tables takes this "warm-up" period into account, so all you have to do is place the meat in the water and time. So simple!

Sous vide cooking has a lot of great things going for it... but there are also a few drawbacks. As you might guess, cooking meat in a plastic bag in water doesn't allow for much browning and that's where a lot of the flavor is developed. There are two ways around this problem. The first, especially if you are using skinless chicken breasts, is to ensure you use a flavorful marinade. The second possibility is to brown the food quickly on the stove top or under the broiler at the end.

While sous vide is a cooking technique that a person could spend a lot of time researching and learning about, in its simplest form, it's pretty straight forward. You place the food of choice into a vacuum sealer bag (you can use zip-top bags, but I'd stick with the heavier duty freezer bags) with your marinade or seasonings. In this case, I used olive oil, a splash of lemon juice, a splash of white wine, thyme, salt, and pepper. Vacuum seal - or close with as much of the air removed as possible. Place in the refrigerator to marinate for a few hours. When ready to cook, place a large pot of water on the stove to heat. I rigged a floating thermometer using some cork and a clothes pin. Heat the water to your desired temperature.

Once the water reaches the desired temperature, place your bag of meat, directly from the refrigerator (41° F) into the water. Begin timing based on the thickness of your meat, using Mr. Baldwin's tables. He has tables for whatever type of meat you are thinking about cooking! When the time is up, remove the bag from the water, cut open, and serve. If you want, you can sear the meat quickly in a pan or under the broiler for additional flavor.

1 comment:

  1. brilliant idea for the floating thermometer. I will have to try that!


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