Sous Vide in the Safety Spotlight

 

Sous vide has become a highly popular method of cooking with home cooks and professional chefs alike enjoying the ease of a long, slow process resulting in delicious dishes packed full of flavour. Literally meaning ‘under vacuum’ in French, sous vide involves the vacuum packing of foods before immersion into a water bath for extended cooking at low temperatures. With just a small amount of prior preparation, food can be left to do its own thing; valuable kitchen time freed up for other time-consuming tasks. Sous vide is a no hassle, convenient way to achieve professional quality with minimum effort.

New to sous vide and have a few reservations? It’s only natural. All instincts indicate that cooking in plastic at ridiculously low temperatures can’t be safe. We’re here to tell you, it is as long as you know what you're doing, and you stick to the rules.

Sous Vide Safety

Is it safe to cook with plastic bags?

To some using plastic bags for cooking over extended periods can seem counter-intuitive however it’s completely safe as long as you choose the right sort. Bags made of food grade polyethylene are perfect. The main concern surrounding combining cooking and plastic is the presence of BPA however this is typically only found in hard plastics, so those bags should be fine. If you can’t find specific sous vide/vacuum sealing bags, named food bags or those that stipulate ‘microwave safe’ will work just as well.

The low temperatures used in sous vide cooking mean that plastic packaging will never heat to sufficient temperatures where a potential risk of chemical transference with food can occur.

Can I reuse sous vide bags?

Reusing equipment is a great way to reduce waste and cut down costs, leading many to question whether it’s safe to reuse sous vide bags. The answer to the query depends on the previous contents. It’s entirely safe to reuse bags, in fact it’s encouraged in waging the war against waste and plastics, however only as along as they haven’t been used to hold raw meat, poultry, seafood or eggs.

Low temperature cooking

The Food Standards Agency (FSA) recommend that foods be cooked to a minimum temperature of 60°C, being maintained in these conditions for at least 45 minutes in order to kill bacteria such as Listeria, Ecoli and Salmonella. This is especially important if wanting to cook and chill dishes. Foods cooked to such guidelines will be considered pasteurised and safe for consumption.

Alternative temperature and time ratios guideline

Internal Core Temperature (°C)	Time Duration to Achieve Pasteurisation
60	45 minutes
65	10 minutes
70	2 minutes
75	30 seconds
80	6 seconds

 

The FSA haven’t released any data for sous vide cooking at temperatures lower than this presumably as 60°C is the upper limit of the ‘food danger zone’. Preparing foods between 55°C and 60°C will require considerably longer cooking durations, whilst being held at consistent temperatures, although there are no guidelines on this practice from the FSA. Certain delicate foods, such as fish for example, are often cooked at lower temperatures. In such cases appropriate documentation of safe practices must be evidenced.

The beauty of sous vide is that it’s mainly based on personal preference (as long as a few safety guidelines are adhered to). Chefs can alter temperatures and the duration of cooking to reflect and achieve the desired result, giving a more flexible approach. Generally, if decreasing temperature, the cooking time will increase. The time and temperature required for acceptable and safe cooking will depend on the type of food, the shape, thickness and weight.

Top Tip: Give foods a quick sear at the end of cooking to produce an unbeatable ‘crust’.

Does sous vide kill bacteria?

The vacuum sealing process required for sous vide removes oxygen from the packaging, without which most bacteria (the aerobic variety) can’t survive. Any that are hardy enough to still be around will be killed off during the cooking process. Anaerobic bacteria (such as botulinum) can cause more of an issue. Capable of withstanding low oxygen levels it is these bacteria that pose a risk if guidelines are flouted. This area is where the issues could potentially lie and so it’s vital to follow strict procedures during cooking and storage.

It’s important to understand that it isn’t the cooking process that is the cause for concern surrounding botulism, but the cooling procedure prior to storage. If cooling and storage are carried out safely and within guidelines there should be no problem. As with all foods, once cooked, standard food safety procedures must always be observed. For more information read on.

Sous vide food should be served immediately or cooled quickly for storage.

Top Tip: Don’t tenderise meat before placing in a vacuum bag – it will expose the inside of the meat to bacteria, an area which would otherwise remain inaccessible.

Food safety and the Food Danger Zone

Serving immediately (the cook-serve process)

Once cooked, maintain foods above 60°C/140°F internally (recommended serving temperature).

Cooling (the cook-chill process)

If planning to cook foods and then cool them, it’s vital to bring the temperature down as quickly as possible between 60°C/140°F and 5°C/41°F to limit any potential growth of bacteria. The area between these temperatures is known as the ‘food danger zone’, representing the conditions most conducive to bacteria reproduction.

Blast chilling is strongly recommended to safely reduce temperatures to as low as 5°C within 90 minutes. Whatever method of cooling is used, food should never stay in the food danger zone for longer than 4 hours.

Storage

Foods cooked sous vide can be refrigerated or frozen in the same bag they were cooked in; ideal for conveniently preparing dishes in advance. Cooked foods should be refrigerated in a fridge 5°C or lower, although ideally below 3°C. If pasteurised (cooked to 60°C), food can generally be chilled for up to 9 days. Storage is entirely safe as long as the seal remains airtight and the vacuum pack remains intact and unopened. It is strongly advised to never store foods for longer than the recommended duration.

Reheating

It is entirely safe to reheat cooked foods straight from the chiller or freezer often using roughly the same conditions as during the original cooking process. If reheating from chilled or frozen remember to adjust cooking times accordingly to accommodate for initial lower temperatures.

If planning on serving immediately, bring foods back up to the original internal temperature. Need a bit more time before service? Reheat to a few degrees lower, allowing foods to sit warming in the water without overcooking. As with the initial cooking process, reheating depends on the size, thickness, weight and type of food.

Top Tip: Always label vacuum bags appropriately detailing contents, date of cooking, time spent in the sous vide and the temperature cooked at. This is a great point of reference when returning to reheat these products.

As long as food safety guidelines are followed anyone can enjoy sous vide food. It’s safe for the very young to very old and all in between - just make sure you stick to the rules and do it correctly.

Choosing Equipment

Selecting appropriate equipment is a sure-fire way to ensure sous vide safety. Look for effective vacuum pack machines (preferably one for use with raw foods and one used for ready-to-eat foods) and a precision commercial sous vide waterbath from brands you can trust, all available at 247 Catering Supplies. A specialist sous vide thermometer is also strongly recommended to accurately monitor the internal temperatures of food.

Top Tip: Always calibrate equipment and document regularly to achieve ongoing reliability and accuracy.

Sous Vide Best Practice

Kitchen staff should all undergo appropriate training in sous vide cooking to guarantee that food safety procedures are understood and guidelines always met. Obviously adhering to the rules is vital to achieving safe sous vide results.

It’s also recommended to maintain a comprehensive log of information to display that strict food safety is observed and a HACCP plan is in place. This will typically include accurate data surrounding water temperature during cooking, core food temperatures, the length that foods are cooked for, cooling times and temperature drops where applicable, storage processes and reheating procedures. This not only gives kitchen staff a fully detailed account for future reference but is also on hand for any future inspections.