Hi Steve, thanks for the question. This is really a pretty involved subject. There are already very good resources out there on the net for sous-vide. For a good introduction I would recommend these pages from the International Culinary Center:
- Sous-Vide Primer, Part I
- Sous-Vide Primer, Part II
For those who are too lazy to click on the links - sous-vide is a method of cooking that involves sealing food in a vacuum bag and then cooking it in a temperature controlled water bath. There are numerous advantages to this cooking method:
- Precision. Food can be brought precisely to the correct cooked temperature. Traditional cooking is done with a high delta-T (i.e. the temperature gradient between the cooking surface / ambient cooking temperature and the food). This means there is a short window of opportunity to remove the food before it is overcooked. Sous-vide slowly brings the temperature up to the desired cooking temperature. The temperature of the food can never exceed the water bath. I have posted a recipe for sous-vide confit ocean trout on this site. There is really no other way to cook trout precisely to 46C without sous-vide.
- Flavour. Any food which is cooked in a solvent (e.g. water in poached, braised, or stewed cooking; or oil in confits) will lose flavour to the cooking medium. For example, carrots cooked sous-vide have an incomparable flavour of fresh carrots when compared to boiled carrots.
- Convenience. Food cooked sous-vide, provided it meets pasteurization criteria, can be considered sterile. It will keep in the fridge longer than uncooked food and can be reheated by simply dropping the bag back into the sous-vide bath prior to service.
- Tenderizing tough cuts. For any food, cooking is a function of (temperature x time). For example, the breakdown of collagen into gelatin is both temperature and time dependent. The rate of breakdown rises with temperature (to an extent) and continues the longer it is exposed to the temperature. This is the principle between "low and slow" barbecues, where tough cuts like short rib are tenderized by cooking at 107C for several hours. With sous-vide, it is possible to cook a short rib such that it is both medium rare and tender - you just set the temperature at 58C for 72 hours. This gives a very different result to barbecued short rib - it is more moist but equally tender.
There are a number of downsides to sous-vide, however. Read the articles for more information, or feel free to ask me.
EQUIPMENT
In general, you need two pieces of equipment:
1. A method of sealing food in a plastic bag;
2. A temperature controlled water bath.
Sealing food - In order of expense: chamber vacuum sealer, foodsaver vacuum sealer, reusable vacuum port bag, zip-lock bag. The difference between all these methods is expense, the amount of vacuum applied, versatility, and ability to seal liquids. The least a sous-vide beginner needs to be able to do is expel all air from the sous-vide bag before sealing it. The reason: air causes the bag to float and acts as an insulator, preventing even heating.
Temperature controlled water bath - here is a breakdown of methods, from ideal to cheapest.
- Immersion circulator, e.g. Polyscience. This consists of a heating element, a PID controller, and a pump. The downside is that it is expensive - however these are the most versatile units around.
- Sous-vide oven e.g Sous-Vide Supreme. This provides most of the benefits of the immersion circulator - however this is a very bulky unit.
- Sous-vide controller e.g. Sous-vide Magic. This is a PID controller that controls another heat source (e.g a rice cooker or slow cooker), and cuts power when the immersed thermometer detects a certain threshold. The heat source can be anything - my heat source is a hot plate with a stock pot placed on it. The main benefit is that it is inexpensive.
Then there are a few non-automated options, which relies on YOU to control the temperature instead of a computer. Needless to say, the great advantage of the computer is the "set and forget" aspect.
- Pot in a pot. Place a pot in a large stockpot over a trivet. Fill both pots with water, and put your food in the inner pot. Heat the outer pot over a hob. The thermal mass of the outer pot will prevent the inner pot from overheating.
- Pot in an oven. Fill a Dutch oven with hot water. Heat the dutch oven until it reaches the desired temperature, then put your sealed food bag in it. Put the whole pot in the oven, and set your oven to the desired temperature.
I think that just about covers it. Any questions - feel free to ask.
OK this is how I do it. Remove the husk from your corn. Get rid of all the silk under running water. Put your corn on a plate with a sprinkle of water (this will help steam up the microwave). Microwave for 45 seconds, then turn your corn over and blast for another 45 seconds. (You probably won't need to do this if your microwave is well designed). Smear on some butter and salt. Eat! I sometimes just eat two ears of corn for lunch at work.
There is no problem putting food from the fridge or freezer directly into the SV machine. As long as it is bagged up and watertight it should be OK.
And another thing ... uncooked meat should NEVER be frozen. The exception is when there is no choice to freeze meat - e.g. tuna or prawns - and even then the meat should be frozen in a commercial freezer. Home freezers damage meat during the freezing process.
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