Health and vitality | Frozen Foods
Fresher than fresh.
One of the best ways to preserve a product’s freshness, flavour and quality is a deep-freezing process. Removing the heat from vegetables, fruit, meat, poultry, fish, bread, cakes, flans and ready meals as quickly as possible preserves them at temperatures that are low enough to prevent microorganisms from multiplying. This locks in the foodstuffs’ vitamins, nutrients, flavour and aroma with next to no loss. As a result, deep-freezing has become one of the best and most popular methods of preserving foods.
Independent experts award frozen foods top marks. Frozen foods can even contain more vitamins than fresh vegetables. This is because the ingredients are invariably frozen on the day they are harvested, locking in their freshness until they are baked and consumed.
Food consists of between 70 and 80 per cent water. When it is deep-frozen, the free water between the cells freezes first. The cells then try to adapt their liquid contents to the external environment and exude more moisture through osmosis. The longer the product is left to freeze, the greater the amount of water that the cells exude.
What then happens when the product is defrosted? Depending on the type of product, foodstuffs can be frozen for up to 12 months before being defrosted (e.g. vegetables for up to 12, fruit for up to 8, fish for up to 6, and crustaceans for up to 3 months). The majority of the moisture emitted through osmosis through the cell walls is then reabsorbed by the cells.
This process is called diffusion, which comes from Latin and essentially means ‘spreading out, distributing’. In biological terms, diffusion is classed as the driving force behind the distribution of the elements within a cell, in which differences in concentration speed up the spread of the molecules.
Consequently, the cell walls are not mechanically damaged by sharp ice crystals during the freezing process, but the cells do irreversibly shrink due to their water content being removed. It is therefore important to make sure the freezing process takes places as quickly as possible. This is all a lot of complicated theory, but it is nevertheless important to know.
What this essentially means for the consumer:
The closer the temperature is to zero degrees, the longer the freezing time is. The cells shrink because they have osmosed too much liquid. The liquid loss is particularly high in the case of fruit, for example, while meat becomes tough and vegetables lose their fresh crunch. Placing beans that you have carefully grown and picked from your own garden in your freezer causes the appliance, which usually runs at a constant –18 °C, to warm up to a more autumnal temperature. As a result, many modern freezers have an acoustic signal designed to warn you that the optimum freezing temperature can no longer be maintained. It then takes days for the core temperature required for freezing to be reached, which consequently leads to frost forming in the freezer due to too much water being lost by the food.
Only freeze small quantities of garden produce and other foods. A freezer’s freezing capacity is the amount of food that can be placed in the appliance within a 24-hour period. All freezers sold in Germany have to be able to freeze at least 7 kg of food within 24 hours, in accordance with a norm issued by the DIN institute. Taking a freezer with a capacity of 100 litres as an example, this sort of appliance has space for approximately 65 kg of frozen food. If 6 kg of food can be frozen per 100 litres of capacity, this should ideally be frozen in 3 batches, each 8 hours apart. Leaving the freezer to rest for 24 hours between putting new food in is also a good idea.
Food should always be stored in the freezer for extended periods of time at –18 °C, as the quality of the food cannot be guaranteed at temperatures any higher than this. Freezers that are suitable for extended storage or for freezing your own food are marked with four stars.
Shock-freezing – the quickest and most effective way to preserve foods
Harvesting food from your own garden is hard work – so why not leave that side of things to the industry instead? After all, the industry is a veritable expert when it comes to preserving foods, having developed the method of shock-freezing. The food is reduced to a temperature somewhere between –30 °C and –40 °C in just 4 to 60 minutes. This speed and these temperatures are just right for maintaining the quality and perishability of foodstuffs.
As a result, produce frozen in this way is fresher than fresh by the time it is sent on its way to the supermarkets. And along the way, the industry and retailers stringently maintain the right storage temperature throughout the chain – in other words, once the produce has been shock-frozen, it is permanently stored at a minimum of –18 °C.
How healthy is fresh food once it is defrosted?
Deep-freezing produce results in food that is richer in nutrients than with other methods of preservation as next to no vitamins are lost at temperatures of –18 °C and lower. It is also the gentlest form of preservation. The nutritional value of deep-frozen foods is consequently unanimously considered by experts to be very high.
Freshly harvested spinach that is immediately shock-frozen is markedly richer in vitamins than spinach that is cooked when ‘fresh’, just 24 hours after having been picked. When boiled in salted water for approx. 10 minutes, the spinach loses its strong aftertaste, but it also loses its valuable nutrients for good. If, on the other hand, the spinach was destined to be a frozen pizza topping, it would be blanched for just 1 minute after having been harvested and would then be shock-frozen. It would then only reach the higher consumption temperature when it was baked in the oven by the consumer.
A brief guide to deep-freezing
Essentially, all the know-how of the deep-freezing industry can only mean good news for the consumer. There are, however, a few things that need to be taken into account if the freshness of the frozen food is to make it to the consumer’s plate:
If at all possible, the freezing chain should not be interrupted between the supermarket and the consumer’s freezer. It is therefore wise to put frozen foods at the end of your shopping list as you go round the supermarket and then to head straight home. When you get back home, the first thing you should do is put your frozen foods in the freezer before you unpack the rest of your shopping. Your freezer should be set at a temperature of –18 °C or lower for food to be stored in the long term. You can, of course, place your frozen foods in the 2-star compartment of your refrigerator. This is not, however, suitable for long-term storage, and this is why frozen food manufacturers always give storage recommendations for the various freezer compartment star ratings. These recommendations can be found on the product packaging.
If the journey between the supermarket and your home is a little further, a practical solution is to put frozen foods in a reusable cool bag or box for the trip home.
Some supermarkets have now even set up a freezer block system which allows shoppers to bring and exchange a freezer block that is part of the system for a frozen one straight from the freezer chests in store. This is a very practical solution for the consumer that also maintains the all-important freezing chain between the supermarket and the freezer compartment at home.
Leaving excess packaging at the supermarket is a good idea in theory, but is not such a good idea in the case of frozen foods. Because the carton a pizza comes in acts as an insulating layer while the product is being taken home. And the packaging also has the product’s best-before date printed on it. This is not so important if the product is going to be eaten fairly soon, but if you tend to store a number of pizzas in your freezer for longer periods, it is a good idea to always store them in their boxes, assuming you have the space. If space is an issue, it is at least a good idea to write the best-before date on the pizza’s plastic wrapper with a marker pen, along with the type of pizza.
For better insulation on the way home, pack frozen foods close together.
Food that is left unpacked becomes dry in a matter of hours. It is therefore very important that food be properly packed/sealed before it is stored in the freezer. And it is particularly important that the container used is airtight in order to prevent other smells, flavours or microorganisms from being transferred to the food.
The packaging used:
should be suitable for food use.
should be resistant to cold.
should not give off oxygen or moisture.
should not give off any odour or flavour.
should be chosen according to the amount of food to be frozen.
Polyethylene freezer bags and vacuum bags, extra strong tin foil, and polystyrene and polyethylene plastic containers all prevent freezer burn.
When unpacked food is stored below zero for extended periods, it can be affected by ‘freezer burn’. This appears as greyish spots on food that has been packed insufficiently or that is stored in damaged packaging, thus exposing it to air and allowing the moisture in the food to evaporate. These patches then react with oxygen, causing the food to discolour. This does not mean that the food is then off, but food with freezer burn does tend to have lost a lot of its flavour and is also tougher. Frozen pizzas therefore come in a plastic wrapping in addition to the carton, to prevent this from happening. Foods that are particularly prone to freezer burn are poultry and meat and also ingredients in ready meals that have been grated too finely to give them the appearance of being more than they are. This is why we at Wagner consciously use a coarser grater setting for the cheese toppings on our pizzas. In fact, our cheese toppings tend to weigh more than others and also tend to melt better. In addition, the cheese protects the toppings under it such as gammon, salami, etc. from drying out.
It is best to defrost frozen foods in the fridge as this prevents any microorganisms that survived the freezing process from becoming active again. A frozen pizza should be put straight into the oven from the freezer compartment. If a pizza is baked straight after having been bought, its baking time should be reduced by a few minutes to take into account the degree to which it might have already defrosted on the way home. Wagner provides cooking guidelines for this sort of situation. You should also bear in mind the fact that all ovens heat up slightly differently. The best indication of a pizza being ready is therefore its cheese topping – when the cheese has fully melted and is slightly runny, the pizza is ready to eat.
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