Don Caswell

In recent years vacuum food sealers have become common, useful household appliances. The special bags used in vacuum sealers provide a superior barrier to conventional plastic bags. This refrigeration of food within an impervious and robust bag has worthwhile benefits, significantly extending storage life.

While undoubtedly useful in the home environment, campers, caravaners, hikers and the like have been quick to seize on the advantages of vacuum sealing as well. Undisputedly functional for sealing food for outdoors adventures, vacuum sealing can also be employed in other aspects of al fresco quests.

The many uses of vacuum sealing

For hikers and kayakers, where the risk of becoming wet is high, vacuum sealing enables gear and clothing to be safely protected from any dunking. A spare set of clothes will collapse to a flat, tight package when vacuum-sealed, making for convenient carry in backpack or kayak. Likewise, electronic devices that need to be carried but are not required on an outing can be safe and secure in a vacuum-sealed bag. Mobile phones and electronic car keys immediately come to mind. These devices do not need to be removed from their sealed bags in order to be used.

Other items that may be needed, such as small emergency packs, compact first-aid kits and fire-starting components are best sealed in trim vacuum bags, protected from the elements but ready for instant use. You are only limited by your imagination when it comes to the sorts of things you can vacuum seal and carry on your outdoor journeys.

However, the primary use of vacuum sealers is for food storage and there are some misconceptions about that which need to be laid to rest.

Vacuum-sealed food must be refrigerated, just like unsealed food. Failure to do this can lead to food spoilage and the risk of illness. I regularly encounter people who want to argue the point about refrigeration of vacuum-sealed food but I can assure you this food requires the same refrigeration that unsealed food needs.

The great benefit of vacuum sealing is that it extends the storage life of food items. With meat, ageing in vacuum-sealed bags provides the bonus of improved taste and tenderness. The safe storage life of vacuum-sealed food depends on the nature of the food involved. The accompanying table provides some guidelines for the safe storage periods of different foods types. As you can see, safe storage periods may be only a few days for some food types, ranging through to weeks, even months, for others. Dried foodstuffs, like rice, have greatly extended storage lives when vacuum sealed.

The science

The science behind vacuum sealing needs to be appreciated. The organisms and chemical reactions that cause food spoilage require three things to thrive – the food itself, warm temperature and oxygen. Refrigeration of food simply represses the multiplication ability of the bacteria that send food off by providing an inhibiting, low temperature environment. Refrigerating vacuum-sealed food gains the combination of minimal oxygen and cold storage that further improves food storage life.

The vacuum appliances on the market suck all the available air out of the bag, which collapses tightly around the food item. Once the machine detects a good vacuum has been achieved, it then heat-seals the bag and its contents. Not just any old plastic bag can be used. The correct bags are of a thicker plastic that is specially made to exclude air (and oxygen) ingress. Ordinary plastic bags do little to exclude air from their contents. The standard for vacuum bags requires an oxygen permeability of less than 50 mL/m² per day under specified test conditions. The correct vacuum bags normally have one interior surface that is textured to assist the vacuuming process.

Safe practices with food storage

A good safety adage from the restaurant business is ‘keep it cold, keep it hot, or chuck it out.’ The temperature danger zone for food spoilage is roughly from 7C to 60C. Keep in mind that most family fridges run around the 4C mark and you can appreciate why food can still go off in the fridge. At 4C you are close to the edge of the temperature danger zone and bacterial growth is just slowed, not stopped. Letting food sit at temperatures in the danger zone is asking for trouble. Food spoilage bacteria can rapidly multiply and cause illness. Likewise, some bacteria can thrive in temperatures approaching 60C, so food in bain marie or warming trays needs to be kept above 60C for safety.

Freezing to -20, or lower, will halt the bacterial growth that leads to food spoilage. The robust vacuum sealing bags that exclude oxygen are ideal for freezing. Unlike the flimsy ‘freezer’ bags sold in supermarkets, proper vacuum-sealable bags can withstand low temperatures, frost and handling without being compromised. The best freezer storage life for vacuum-sealed food is around two to three years, compared to about six months, or less, for food frozen in conventional bags. Freezer burn becomes a thing of the past once you start freezing your stored food in vacuum-sealed bags. There are a few issues around defrosting frozen foodstuffs that need to be considered.

Defrosting of frozen foods is best done in the refrigerator. When you need to defrost food in a hurry, then the best options are to place the sealed food in a container of cold water or use your microwave. Personally, I do not like defrosting food in the microwave as it causes partial cooking. The other point about microwave defrosting is that having warmed the food, it needs to be cooked immediately. Leaving a bag of vacuum-sealed food to sit out at room temperature all day is a bad practice that carries a significant risk of food poisoning.

Another important point which many folks fail to appreciate is that food can be off without any visual or odour warning signs. Some of the bacteria that cause sliminess and bad smell are not particularly dangerous themselves while the real bad boys do not give off any such warnings. The fact that both sorts are likely to be present when food has had the right conditions for spoilage has led people to rely on the look and smell test. It is not a trustworthy indicator of potentially dangerous spoilage.

The other foundation block of safe food storage is good hygiene practices. Clean preparation surfaces, clean utensils and clean hands are a must. A tub full of hot, soapy water and plenty of clean wash-clothes always accompany any of my food vacuum sealing projects.

If you understand the basics behind vacuum-sealed food storage, and practise good hygiene and handling, you can ensure some great meals in the wonderful outdoors during your travels.

Refrigeration storage life – unsealed food v vacuum-sealed

This is a rough guide, not gospel. Actual storage life depends on many aspects, including hygiene, the state of the food going into the fridge, the temperature of the fridge etc.