Cooking is defined as the use of heat to induce chemical reactions in food, with different effects taking place on the food at different temperatures. Cooking an egg is a perfect example of this. The different proteins in egg albumin coagulate at specific temperatures and a few degrees difference in cooking temperature will affect how much the egg white solidifies. The texture of the egg yolk changes as its temperature rises.

Temperature affects other proteins in a similar way. Meats with a high collagen content, such as chuck and brisket are normally cooked for longer periods of time at higher temperatures in conventional cooking, so as to break down the tough collagen to make the food palatable. Conversely meat with little connective tissue such as prime rib, can get too tough if cooked at high temperatures for long periods of time. The temperature at which meat is cooked can make a critical difference to the palatability of the meal.

The key to sous vide is cooking at low temperatures for long periods of time. The cooking time and temperatures are determined by factors such as the type of food, the mass of the food, the core temperature of the food and the heat transfer characteristics of the food. In sous vide cooking an accurate temperature and an accurate cooking time is determined to achieve perfect results. It is vital to use equipment such as the Grant Universal Stirred Heaters or Grant Precision Sous Vide Baths in sous vide cooking which control temperature within a fraction of a degree. Slow cookers, simmering pans and baine maries do not offer the precision in temperature, that proper sous vide cooking requires. This is vital to the success of sous vide cooking and it has the added benefit of completely consistent results. Grant Universal Stirred Heaters or Grant Precision Sous Vide Baths circulate the water while cooking, ensuring that the food does not develop hot and cool zones that adversely affect the cooking process. They stabilise the temperature and transfers heat into all vacuum packed bags rapidly and evenly. Differences of even one degree can affect the finished product

In catering facilities which use the sous vide method it is very important to have a well managed food safety system to eliminate unwanted bacteria and pathogens. The most critical factor in any food handling is temperature control. Temperature has the greatest impact in suppressing bacterial reproduction and ensuring that perishable items, especially proteins, stay out of the danger zone of 3° C (37°F) to 60°C (140°F). Cooking at low temperatures only kills vegetative forms of pathogens. Under ideal conditions, bacterial counts can double every 20 minutes. In 12 hours, a single bacterium may multiply exponentially into a colony of over 9 billion. It is therefore vital that correct equipment is used at the correct temperatures.

The following table displays temperature safety zones in pasteurisation:

Assured Pasteurisation zone: > 63°C +
Start of Pasteurisation zone: 60°C – 63°C
Tolerance zone: 55°C – 60°C
Danger zone: 50°C – 55°C
Extreme Danger zone: 20°c – 50°C
Danger zone: 10°C – 20°C
Tolerance zone: 3°C – 10°C. (Most food preparation takes place in this temperature zone)
Secure zone: < 3°C

Sous vide cooking is usually finished off by a brief grilling or blowtorch searing, creating the familiar aromas and flavours that come only with conventional high temperature cooking. The distinct difference with food cooked using the sous vide technique and finished in this manner, is that the interior remains exceptionally tender and tasty while there is minimal shrinkage, compared with that of traditionally grilled or roasted meat.

Recommendations for sous vide cooking

• Grant Universal Stirred Heaters or Grant Precision Sous Vide Baths are recommended for this type of cooking.

• Fresh ingredients from trusted suppliers must be used for sous vide cooking. This can significantly lower initial microbial levels, extending shelf life and product freshness.

• Vacuum packed bags of raw food must not be stored for more than two days before sous vide pasteurization above 60°C (140°F) takes place.

• Separate preparation areas for raw food and cooked food must be allocated in the sous vide cooking area.

• All working surfaces and utensils must be kept hygienically clean.

• Temperature and cooking times in recipes must be followed precisely and when new recipes are developed, precise temperatures and cooking times must be recorded.

• All sous vide equipment must be checked and calibrated. Vacuum pack seals should be checked for leakage.

• Attention must be given to accurate temperature control and monitoring as sous vide especially since foods lack chemical preservatives, which normally arrest biological activity in processed foods.

• Core temperatures should be measured with a temperature probe, which should be hygienically cleaned.

• Cooking temperatures must ideally not exceed 70°C to ensure that the juiciness of the food is not lost.

• Vacuum packed bags must be labelled accurately with date of pasteurisation and expiration, identification of contents and name of the chef who prepared the food.

• Sous vide food must be cooled to 3.3° C or below in less than 2 hours and consumed within the specified shelf-life storage time.

• Sous vide food must be stored at 3° C or below.

• Proper control over refrigerator temperatures must be kept, especially in the case of walk-in fridges where temperatures can rise above the required storage temperature.

The temperature reached in regenerating sous vide food for serving, must be the same as that required in conventional cooking.