Safety with food
We all have doubts sometimes whether the food we stored, prepared, cooked or cooled is still safe to eat when we are travelling.
We do not have the same kitchen facilities as we do at home so we are constantly juggling our food in an attempt to keep it hot or cold or even just the flies away from it.
The Australian Food Safety Standards have been devised primarily for the commercial handling of food, whether that food is to be sold or given away, and is therefore a good guideline when considering the safe parameters for food handling for your family and friends own consumption.
Basically the rules are:
Hot food should be kept at 60 degrees or over and Cold food should be kept at 5 degrees or less.
Between the temperatures of 5 and 60 degrees, potentially hazardous food is susceptible to growing bacteria, resulting in stomach upsets or food poisoning.
The following is taken from the Food Standards Australia website http://www.foodstandards.gov.au/
Examples of potentially hazardous foods:
- raw and cooked meat or foods containing meat, such as casseroles, curries and lasagna;
- dairy products, for example, milk, custard and dairy based desserts;
- seafood (excluding live seafood);
- processed fruits and vegetables, for example, salads;
- cooked rice and pasta;
- foods containing eggs, beans, nuts or other protein rich foods, such as quiche and soy products;
- foods that contain these foods, such as sandwiches and rolls;
Cooling potentially hazardous food
If you cook potentially hazardous food that you intend to cool and use later, you need to cool the food to 5 degrees or colder as quickly as possible. There may be food poisoning bacteria in the food even though it has bee cooked. Faster cooling times limit the time when these bacteria are able to grow or form toxins.
The standards require food to be cooled from 60 degrees to 21 degrees in a maximum of two hours and from 21 degrees to 5 degrees within a further maximum period of four hours. If you don't know how fast your food is cooling, use a portable thermometer to measure the warmest part of the food - usually in the centre. For more information about the use of thermometers, see the fact sheet "Thermometers and their use with potentially hazardous food"
To chill food quickly, break it up into smaller portions in shallow containers. Take care not to contaminate the food as you do it.
Reheating previously cooked and cooled potentially hazardous food.
If you reheat previously cooked and cooled potentially hazardous food, you must reheat it rapidly to 60 degrees or hotter. Ideally, you should aim to reheat food to 60 degrees within a maximum of two hours to minimise the amount of time that food is at temperatures that favour the growth of bacteria or formation of toxins.
Ingenious methods of prolonging the "Safe" handling of foods.
The Hay Box.
The hay box was a very successful, although not very portable, method of slow cooking using the heat retention principles of packed straw insulation.
The food was brought to the boil, usually in a heavy cast iron pot, and then the whole pot was placed in a crate and straw was densely packed around the pot to "hold the heat in"
This method proved very effective where fuel was scarce and people worked long hours away from the home.
This method was also used as cold retaining devise where foods were often left outside during the chill of the evening and then packed in the crate with straw during the warmer day time temperatures.
The New Zealand Hungi.
Slow cooking in the ground has long been used to provide succulent, tender and juicy meals, but it also ensured that these foods stayed well over the 60 degree food safety temperatures for many many hours during the cooking process.
Baked in Clay.
Another ingenious adaptation for slow cooking (above 60 degrees) was the principle of coating the food to be cooked in a heavy moist clay and then slowly baking this clay covering in the coals.
The Clay would then retain the internal temperature of the food inside for many hours.
This method was particularly appropriate for any meal where the outer covering was bothersome such as fur, scales, skin or a coarse rind etc as this would stick to the clay coating and would come away relatively cleanly when the "Clay pot" was broken open to eat.
The Coolgardie Safe.
The Coolgardie Safe was an excellent "bush" adaptation to the old problems of keeping foods cooler than the outside temperatures.
An aerated box (either fly wired covered or pressed perforated metal) was covered with Hessian on all sides and that Hessian was draped so that the ends were in a constant supply of water from a tray underneath.
The water would "wick" up along the Hessian and dampen the whole cloth.
The Safe was hung in a breezeway so that the prevailing breeze could assist with the constant evaporation from the Hessian.
This constant evaporation created a distinctly cooler atmosphere within the safe and thus kept the contents cooler than the outside atmospheric temperatures.
Introducing the Vacuum Chamber
Vacuum insulted technology was invented well over 100 years ago and was commercialised in 1904.
The principals of vacuum evacuation technology are very simple:
- When you have a sealed double wall chamber, the air within that chamber is a slight insulator however air molecules will warm and transfer that warmth to each other and eventually the outside atmosphere.
- If you fill that chamber with foam it will create a better insulation however the foam is still full of tiny air bubbles that will warm up and eventually pass that heat through the next molecules and finally to the outside atmosphere.
- When you take all the air out of that chamber (vacuum evacuation) there are virtually no molecules available to transfer the heat through and hence the product inside will retain its temperature for the longest period.
It should be noted here:
- That transmission of heat through the walls of the chamber is the main area of contact with the outside atmosphere.
- A small amount of heat can also be transmitted by the surface of the wall material by conduction to the very lip of the container.
- The material of the evacuated chamber extends from the inside of the container to the outside as it is a continuous sealed unit and therefore a small amount of heat can be lost this way.
- The lid sealing the chamber is usually not an evacuated chamber and is usually foam insulated and therefore once again heat can be lost through this medium.
Modernising yesterday's technologies:
- The original evacuated chambers were glass and had a cumbersome lump at the bottom where the air had been evacuated from and then the glass chamber melted closed.
- This glass construction meant that Thermos Flasks were quite thick and heavy.
- The valve mechanism was also the cause of many air leak problems resulting in poor thermal insulation properties.
- Today the technology has been re-patented to encompass new principles whereby the whole chamber is now manufactured by robotic machinery within an evacuated chamber.
- When the finished product comes out of the evacuated chamber the THERMOS is already fully evacuated and therefore has no need for cumbersome valving.
- This new technology ensures that the new models are light weight, stronger and able to hold much greater capacities than the THERMOS of old.
Thermos Shuttle Chef Slow Cookers.
The Shuttle Chef consists of two types of containers.
Heavy duty, stainless steel, inner saucepans for direct heating and a patented outer vacuum insulated container, both manufactured for maximum heat retention.
The inner saucepan has a multi layered stainless steel structure with a carbon steel plate sandwiched in the heavy duty base for high lateral heat conductivity, resulting in heating from all directions.
The meal is prepared in the inner saucepan and brought to the boil, then simmered until all of the meal is approximately the same temperature then this saucepan is placed inside the insulated outer container and the lid is closed.
The heat retained in the inner saucepan slowly cooks the food for hours, you do not need to keep checking it while it is cooking and it will stay above food safety standards for 8 hours plus.
This means that food preparation and safety just got a whole lot easy and safer as you can now prepare a meal in the mornings, when it is cooler and less tiring and use a minimal amount of cooking time and obviously heat energy.
This meal will go on slowly cooking for at least 8 hours, tenderising the meat, and yet it will not break down the colour, shape and texture of vegetables, resulting in a highly nutritious (no evaporation of nutrients) wholesome meal.
The dinner or evening meal can be enjoyed without further preparation, other than opening a bottle of wine and buttering some crusty bread.
Food prepared and cooked this way ensures that it stays well within the food safety guidelines outlined above without constant energy inputs and is in fact a healthier approach to food and the conservation of energy...not to mention the stress levels of trying to cook nutritious meals in a caravan, motor home or tent at 5.30pm on a stinking hot summers day.
This same principle applies equally to keeping foods cold as the temperature inside is unable to absorb heat from the outside through the vacuum chamber and therefore can only absorb small amounts of heat via conduction at the lip and through the foam in the lid.
In actual fact the vacuum concept works even better for retaining cold temperatures than it does for retaining heat and even the foam insulation in the lid performs better.