Tuesday, 25 December 2012

Sous-vide cooking, boil in a bag technology


Sous-vide French for "under vacuum") is a method of cooking food sealed in airtight plastic bags in a water bath for longer than normal cooking times—72 hours in some cases—at an accurately regulated temperature much lower than normally used for cooking, typically around 55 °C (131 °F) to 60 °C (140 °F) for meats and higher for vegetables. The intention is to cook the item evenly, and to not overcook the outside while still keeping the inside at the same "doneness", keeping the food juicier.
In most cases, cooking sous vide simply involves two steps: the sealing of foods in plastic bags and submerging the bags into hot water baths for a period of time to heat through. The water is typically regulated at the desired final temperature of the food or just above. The food is held in the water bath until it reaches the same temperature as the water (and then held at that temperature until service or a final cooking step takes place such as searing). In many ways, this is similar to simmering (such as in a poached fish recipe), except the sous vide water is usually at a lower temperature and food is kept from making direct contact with the water by a barrier (such as a plastic bag or eggshell in the case of sous vide eggs, thus minimizing flavor and nutrient loss of the ingredients to the cooking liquid).
The theory was first described by Sir Benjamin Thompson (Count Rumford) in 1799 (although he used air as the heat transfer medium). It was re-discovered by American and French engineers in the mid-1960s and developed into an industrial food preservation method. The method was adopted by Georges Pralus in 1974 for the Restaurant Troisgros (of Pierre and Michel Troisgros) in Roanne, France. He discovered that when foie gras was cooked in this manner it kept its original appearance, did not lose excess amounts of fat and had better texture. Another pioneer in sous-vide is Bruno Goussault, who further researched the effects of temperature on various foods and became well known for training top chefs in the method. As chief scientist of Alexandria, Virginia-based food manufacturer Cuisine Solutions, Goussault developed the parameters of cooking times and temperatures for various food.
Sous-vide has become a common feature on television cooking shows. It has also been used to quickly produce significant quantities of meals for hurricane evacuees. Non-professional cooks are also beginning to use sous-vide cooking.
Clostridium botulinum bacteria can grow in food in the absence of oxygen and produce the deadly botulinum toxin, so sous-vide cooking must be performed under carefully controlled conditions to avoid botulism poisoning. Generally speaking, food that is heated and served within four hours is considered safe, but meat that is cooked for longer to tenderize must reach a temperature of at least 55 °C (131 °F) within four hours and then be kept there, in order to pasteurize the meat.

Pasteurization kills the botulism bacteria, but the possibility of hardy botulism spores surviving and reactivating once cool remains a concern as with many preserved foods, however processed. For that reason, Baldwin's treatise specifies precise chilling requirements for "cook-chill", so that the botulism spores do not have the opportunity to grow or propagate. Extra precautions need to be taken for food to be eaten by people with compromised immunity. Women eating food cooked sous vide while pregnant may expose risk to themselves and/or their fetus and thus may choose to be more careful than usual.
Sous-vide's failure to penetrate the home kitchen is in part because of expense. A typical water-bath for the domestic cook, will cost £499, along with a good vacuum-sealer too cost at least £50.
One limitation of sous-vide cooking is the fact that browning (Maillard reactions) happens at much higher temperatures (above the boiling point of water). The flavors and "crust" texture developed by browning are generally seen as very desirable in the cooking of certain types of meat, such as a steak. The flavors and texture produced by browning cannot be obtained with only the sous-vide technique. In many cases, meats and other foods cooked with the sous-vide technique will be browned either before or after being placed in the water bath, using techniques such as grilling or searing on an extremely hot pan.

The whole process of cooking a ready meal in a bag for longterm storage offers the convenience to quickly heat up, eat and go ready meal. While the equipment is relatively expensive, its seems that this type of cooking maybe left for the convenience of large restaurants and emergency food packs for hurricane evacuees. Comparing the effort of a typical weekly shop to buying preparing and freezing enough food for the week, seems to be too much of a chore for Sous vide. Also the novel factor of this type of cooking would probably wear off in a few months, and would just seem like boil in the bag cooking. A simple task synonymous for boiling rice or cheap ready meals for a students with a budget...



2 comments:

  1. Your blog are impressive to each other.I read your blog its very good and friendly, it'll help full to all.

    Regards
    Milltecmachinery
    http://www.milltecmachinery.com/about-us.html

    ReplyDelete
    Replies
    1. Thanks for the comments it makes my day. Love to learn new stuff and write about it....

      Delete