Wednesday, April 28, 2010

Sous-vide at home for $15

Sous-vide is a cooking techniques that deeply appeals to the geeks among us.

I love collecting data, so out of curiosity I often ask my students if they are familiar with the sous-vide method. According to the stats I've collected*, about 6% of you are thinking at this point, "Gee, Helen, what took you so long?" While the other 94%, are thinking, "Sous-what?"

Since most people are thinking, "sous-what," let me start with that. Sous-vide means cooking food in a vacuum sealed bag submerged in water held at the desired doneness temperature. It is a cooking method that became popular in professional kitchens in France in 1970s and in the US in 1990s. What's so good about it? Perfectly even doneness. Normally, when proteins are cooked, they get tough and dry. Good cooks try to minimize this negative effect, but there is only so much we can do when using traditional methods. To make sure we don't ruin the entire steak, chicken, or fish, we take residual heat into account. In other words, we under-cook proteins, then let them rest at room temperature allowing the center to reach desired doneness and the edges to cool off. With sous-vide, all this guesswork goes out the window. If you want to eat steak at 130F, you set the temperature of your water to 131F, put in a vacuum sealed steak, and wait long enough for it to reach that temperature. I am sure you've eaten steak before where some bites were better than others. In this steak, every single bite is absolutely perfect**.

The practical question that begs to be asked here is how exactly do you keep water at 130F or any other exact temperature. The only one that's easy to achieve is 212F. That's the temperature at which the water boils and even if you keep it on high heat, it won't go over 212F. But 131F? That's where an immersion circulator comes in -- a pot that continuously measures and adjusts the temperature of the liquid commonly used in science labs. The cheapest one on the market today is about $500. Add to that $100 for the cheapest vacuum sealer and for a mere $600 you could be using the fabulous sous-vide methodology at home.

Before you say "forget about it", let me point out that a careful cook can fake some of this equipment for about $15 using a zip lock bag and a digital meat thermometer. You put food in a zip lock bag, suck out as much air as possible, and use a thermometer to monitor the water in your pot. If too cold, turn up the heat; if too hot, dilute with ice water. Is it really that easy? Well, let me put it this way -- it's not for people who get easily distracted. Will all your sous-vide dreams finally come true for $15? I only wish. My little set up only works for quick cooking dishes like fish fillets, shrimp, eggs, and chicken breasts (phenomenal cooked sous-vide style and seared for a minute to crisp the skin). Remember that sous-vide uses very low temperatures and things take much longer to cook than you are used to. Short-ribs can take as long as 3 days. Not only would you not want to stand by your pot with a thermometer that long, but you would be risking poisoning your dinner guests without proper vacuum sealing and absolutely perfect maintenance of temperature. Even 1 degree can make a difference. That's why I stick to foods that can be cooked within 2 hours (not enough time for harmful pathogens to grow).

Now the details.

June 15, 2010 update:  since writing this post, I found out about a much easier way to get air out of zip lock bags -- slowly submerge them in water and seal. And, to maintain water temperature for a long time, use a very large beer cooler instead of a pot.  Here is the post.

Faking the vacuum sealer

I use heavy zip lock bags. No, they won't melt. Remember, you are keeping the temperature at under 141F. That's cool enough to touch with your hands without getting burnt. The hardest part is getting the food into it and sucking out the air. You don't want the food to touch bag's opening since you'll have to touch it to your lips to get as much air out as possible. One possible solution is to put your food on a piece of parchment paper or foil, fold it in half and slide it into the zip lock bag. Let the food drop into the bag and then carefully remove the paper. Zip the bag almost all the way, and suck the air out through the leftover opening. When you get as much air out as possible, quickly shut the bag. If you don't get enough air out, the bag will want to float instead of submerging in the water. After messing with zip lock bags for a while, I finally got myself a vacuum sealer for $100 and am very happy with it (Cook's Illustrated recommendation, of course :).

Faking immersion circulator


I have 2 words for you: Large Pot. The more water you have, the longer the temperature will hold without you tinkering with it. I use an 8 quart stock pot even when cooking 1 Lb of food. To get the right temperature to begin with, let your tap water warm up, then hold thermometer under the stream and regulate the water until you get as close as possible (but not over) your desired temperature. For fish and poultry, I use 141F. If your tap water doesn't get hot enough, warm up the water on the stove top while stirring and measuring with the thermometer constantly. When you reach the desired temperature, turn off the heat. Put in your food, close the pot with a lid and check it every 5-10 minutes. You'll need to check more often toward the beginning since the food you just added is cold and will make the water temperature drop, but as the food warms up, the water temperature will hold steady longer.

If the water temperature drops, turn on the heat under the pot, stir the water and measure the temperature until you get it right. If you overheat the water, pour some off, add cold water, stir, and measure the temp. Yes, it takes some patience. A note about thermometers: the first number you'll see as you place the thermometer in the water is misleading. My $15 thermometer takes 14 seconds to stabilize. You can get one that stabilizes in 3 seconds, but that costs $100. So, get to know your thermometer. When the temperature changes less than 1 degree in 5 seconds is when you should start trusting it.

When is it done

While I normally tell people to err on the side of under-cooking (to allow for risidual heat), with sous-vide you need to do the opposite. Your food can't overcook since it's held at the ideal doneness temperature. Since your food is in a bag, you can't cut it or stick a thermometer into it to judge its doneness. So there is no use looking for the moment when the food is "just done". The best way to figure out how long to cook your food is to consult the following table that I got out of A Practical Guide to Sous Vide Cooking by Douglas Baldwin.

Pasteurization Time from 41°F (5°C)
Thickness136°F141°F 146°F151°F
mm57.5°C60.5°C 63.5°C66°C
51:4031105
101:45361510
151:53442317
202:04553426
252:181:094638
302:351:251:0151
352:551:441:171:05
403:182:051:361:22
453:442:281:561:40
504:122:542:171:59
554:433:202:412:20
605:163:493:062:43
655:524:203:323:07
706:294:524:013:33

Yes, sous-vide takes way longer than other cooking methods, but the beautiful thing is you don't have to serve your protein immediately. If your fish fillets are done, but your side dishes aren't, no harm done. Just maintain the temperature in your water bath until ready to serve.

Sous-vide is really a god-send for home cooks since doneness is their biggest pitfall (that, and not using enough salt). I've built a whole business on the simple premise of teaching people when fish, meat, poultry, and vegetables are done. If I don't watch out, I might be put out of work by a plastic bag and an immersion circulator. But I am guessing that is not going to happen just yet :) And when all of you are armed with an immersion circulator, expect to see a sous-vide class from Helen's Kitchen. My guess is that in 5-10 years, this might actually happen.

* Of course, this relies on the assumption that my students and blog readers are two very similar populations.

** There is a similar technique of slow roasting meats in 250F oven and searing in the end. It produces results very similar to sous-vide for tender cuts of meat. I actually prefer it to sous-vide because it results in a drier outside of meat, which means faster searing, which means less ruining of the perfectly even inside. I learned this technique from Kenji Alt at Cook's Illustrated. Here is his recipe for a perfect steak.