Cooking at low temperatures "sous vide"

[edsel]

Thanks for participating in this Q&A.

There's been considerable interest in low-temperature cooking in vacuum-packed plastic bags ("sous vide") here on eGullet. Here is a representative topic. I have a couple of questions and concerns:

It's been stated that the temperatures need to be maintained within a very narrow range. I purchased an immersion recirculating heater, intended for laboratory water bath use, that is claimed to be accurate to 0.5 °C. If a recipe calls for the use of a commercial steam ("combi") oven, am I right to assume that my water bath will produce similar results if set to the same temperature? In other words, will the temperature-transfer characteristics of a water bath produce the same results as a steam oven?

Also, just how critical is the temperature tolerance? I have a vague, fuzzy mental image of protein molecules behaving differently at low temperatures compared to more conventional cooking techniques. Does a small change in temperature really affect the texture of the food to such a great extent?

Some of the temperatures used are much lower than conventional cookery. Sealing the food inside the plastic bag supposedly protects against contamination, but what about anaerobic bacteria? Does the vacuum-sealing process actually increase the chance of developing botulism? How great is the increased risk of cooking at low temperatures for extended times? I've seen techniques that call for cooking times as long as 36 hours. I'm not squeamish about raw or rare foods - I enjoy eating sushi, sashimi, and steak tartar when I trust the cleanliness of the source. I'm not too keen on poisoning myself or my friends....

Sorry to be so long-winded. I really appreciate the input of people who have the discipline to research the scientific aspects of food. Thanks again for joining us here on eGullet.

[Harold McGee]

Cooking sous vide is an interesting process in a number of ways, one of them being the microbiology. The FDA was concerned enough about the potential for spectacular food poisoning that in the 1980s they strongly recommended against its use. But those concerns have not been borne out in practice. The way I understand it is that while the cooking temperatures may not be high enough to kill all bacteria and spores, they are high enough to discourage their growth: and then the rapid chilling and continuous cold chain prevent growth during storage. While it may not be essential to maintain the cooking temperature within a degree F or 0.5 C, good temperature control is critical to make sure that the bag doesn’t become an incubator. A water bath set to the same temperature as a combi-oven should produce a similar result.

[edsel]

Your take on the safety issue pretty much matches my intuative understanding. I don't cook "sous vide" in a commercial environment, so I'm not usually doing the cook-ahead-and-hold-for-service trick. I'm just fascinated by the unique textures that result from the technique.

Jackal10 has a related question here about the safety of low-temp cooking. He mentions needing technical information to show the "food police". There are rumors that the FDA is increasingly suspicious of these methods, and I gather that something similar is afoot in the UK.

Thanks again for joining us this week. You've been barraged with questions - not surprising considering the broad range of interests here. I'm looking forward to reading the new edition of your book.