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An Introduction to Food Preservation

During the summer, I diligently fed and watered what I had planted in my polytunnel: every day I was in there, sweating when it was particularly warm and feeling smug when the rain was hammering down on the plastic above me. I pruned the tomato plants, removed dead foliage and encouraged the buds to grow. In return for my care and uplifting chatter, we were delighted to pick cucumbers, courgettes, chillies, some aubergine, strawberries, beans and a greedy abundance of tomatoes.

Ripe Aubergine Ready to be Picked (July 2020)

If I’m honest, the idea of Misty Green Living had not yet entered my head, so my rather slap-dash approach was centred on the plants that I could pick up in the local cash-and-carry store which had a small garden department attached. The world had stopped because of the Corona Virus and our actions were confined by geography (how far we could travel) and availability (fruit and vegetable plants were particularly hard to come by due to the unforeseen growth in demand). I filled the spaces in our lives and garden with the hope of tasty delicious treats for the family, and boy, did we get growing!

While undoubtedly rewarding, growing your own produce does also bring with it the challenge of harvest time: when all those tomatoes start to ripen, a few a first and then by the boat-load, they will not last indefinitely off the vine. This is where food preservation comes in: we must ‘do’ something to all those extra tomatoes to prevent the surplus from spoiling.

Food preservation is any process that is undertaken to slow the spoilage of food and ensure it can be stored and eaten at a date later than it could be enjoyed if left unprocessed. Incredibly, while this may sound complicated, we are used to eating these foods and have them tucked away in our fridges and larders: Jam, pickles, tinned fruit, frozen vegetables, tomato ketchup, even items like cheese and yoghurt, the list goes on and on.

Why Preserve Food?

All food, be it plant or animal based will spoil over time because of the growth of microbes that are present all around us. These microbes - different microorganisms and yeasts – will in turn produce toxins as they grow and develop and when this happens, the food becomes harmful to us. Thanks to them, over time, an item of fresh produce will go from being ‘delicious’, to ‘a bit squishy and overripe’, to the ‘super furry animal’ stage and eventually it will become the congealed mess that you find at the bottom of your crisper drawer.

Tomatoes from the Polytunnel (August 2020)

While we now have a wonderful availability of foods regardless of the time of year, this used not be the case. When the harvest of those tomatoes we mentioned earlier finished, that was the end of tomatoes until they ripened again the following growing season. Obviously, folks learned to preserve: fresh food could then be kept and enjoyed for longer, but more importantly, it would be safe to consume.

These preservation methods were passed on throughout the generations and we still use them today. Incredibly, archaeologists have found evidence of food preservation by drying (or dehydration) which dates back to about 12,000 BCE! Despite our developments in technology and industry many centuries later, this is still a hugely popular technique for many types of crop.

Types of Food Preservation

Cool Storage

In our modern kitchens, our first port of call for lengthening the shelf-life of fresh produce is the refrigerator – the life cycle of microbes already present on the food will be slowed down by reducing the temperature and chilling it, which means that the item will last longer. Unheated basements, pantries and root cellars also serve the same purpose.

Examples of food stored this way: root vegetables (potatoes, carrots, turnips, beetroot and parsnips), onions, apples, garlic, pumpkin, squash, meat and dairy products.

Dehydrater, Filled with Camomile Flowers and Herbs


By removing moisture from the food, the conditions within it are made inhospitable for the microorganisms to thrive. We can do this by air-drying, drying in the sun or by using a dehydrator.

Examples of food stored this way: fruit, vegetables, herbs, spices and meat.

Water Bath Canning

Filled jars are placed in a bath of boiling water so that they are submerged. The temperature is maintained at boiling for a period of time and any potentially harmful microorganisms are killed by the extreme heat. The air is also driven out of the jars during this process and a vacuum seal is formed which allows them to be stored for longer.

Examples of food stored this way: high acid foods (like fruits), pickles, chutneys and ketchups.

Pressure Canning

This method is similar to water bath canning, but a special pressure canner is used to increase the pressure and as a result, the temperature within the canner. Temperatures should reach up to 115⁰C (about 240⁰F) and it is important that the correct equipment is used for this method – a pressure canner will measure the pressure accurately using a gauge - otherwise the resultant stored food may be unsafe for consumption.

Examples of food stored this way: low acid foods (like sauces, soups, meats and even dairy).


By reducing the temperature, again the growth of microorganisms is halted. The flavour, freshness and texture of so many different foods can be stored this way and often the only limit to freezing is the size of your freezer.

Examples of food stored this way: meats, fruit, vegetables, sauces, soups, cooked rice and pasta.


Now this is where it starts to sound really complicated, but really it’s just natural processes being allowed to take place. Fermentation is a when bacteria or yeasts (microorganisms) present in food are in an environment without oxygen and are allowed to feed on the sugars present. They convert those sugars into alcohol or other acids.

Examples of food stored this way: wine, beer, dairy (in the form of cheese and yoghurt), kimchi, sauerkraut and even sourdough bread.

Preserving in Salt

Salting and brining are skills that we are less likely to be familiar with, but we enjoy these foods all the time. The salt draws the water out of the food and thus inhibits the growth of microorganisms.

Examples of food preserved this way: salted fish, bacon, corned beef

Preserving in Sugar

Again, by increasing the amount of sugar in a food, it becomes an environment unfit for the growth of microorganisms.

Examples of food preserved this way: jams, jellies and cordials.


By adding vinegar, the acidity of the product is increased so that it any microbes present are killed off. This process also causes the texture, colour and flavour to be changed, and often salt, spices and sugar are added for a huge variety of flavours.

Examples of foods preserved this way: fruits (like apples and plums), vegetables (like onions, beets, peppers, carrots onions, cauliflower, green beans) and chutneys.


Alcohol draws the moisture out of the food, so it works much like the way using salt or sugar does, stopping the growth of microbes.

Examples of foods preserved this way: infused alcohols, extracts, fruits.

Other Methods

Olive Oil preserving needs to be approached with some care, in particular when dealing with low acid foods like garlic as there is a risk of the growth of the bacterium ‘Clostridium Botulinum’. For this reason, I try to steer clear of it – there are so many other options to choose from in any case.

Freeze drying is another option but I have never tried it and from any research I have done, a freeze dryer is an expensive piece of kit that I am not overly excited to obtain. Again, there are other options available.

How Long Will It Keep?

As this is a blanket question, I won’t answer. It completely depends on the food type and the method used so we’ll go into a bit more depth about the various techniques one by one at a later date. If you are new to food preservation, it is worth doing your research and having a couple of reliable books that can be trusted in your home library.

Can All Methods be used for All Foods?

For the most part, yes, but the result will not always be favourable.

For example, can I freeze lettuce? Yes, I can. Would the lettuce be safe to eat on thawing? Yes, it would. Would it be a pleasant experience to eat that lettuce, soggy and limp and most likely leaking juice all over the place? I’ll leave that up to you to decide.

There are definitely some methods that are more suited to particular food types: soft fruits do

Pickled Eggs: A Delicious Treat

well as jams and jellies, but also can be dehydrated or frozen. Some vegetables are wonderful when made into pickles and chutneys while others really lend themselves to being dried, like legumes. Meats can be canned from what I hear, but I predominantly freeze it for future use.

Different methods of preservation will also affect the nutritional value of the end product too, so that will be a factor in the method we choose– we obviously want to be able to retain as many of the vitamins and minerals for a more nutritious end product.

How Do I Master These Food Preservation Methods?

With training, time, practice and care.

Food preservation techniques are invaluable, especially if you grow some of your own food, but learning them is not to be taken lightly. There are certain rules that must be adhered to, and if you stray from the instructions supplied, you risk the process failing. At best, this means that your jam grows mould and cannot be eaten, but at worst, an improperly canned item could cause botulism which can have fatal consequences.

Making Jam is a Great Place to Get Started

I’m not being overly dramatic here. I do want you to be aware that food preservation techniques are not like baking. If you bake a cake, there is nothing that you can do to flour, sugar and eggs that will kill you - your cake may not rise, the quantities may be off or you may burn it - the result may not taste as you hoped, but you can try again after you’ve brushed off your ego.

I really do recommend finding a book or some other trustworthy source to guide you while learning: there are many good resources available. Also, just a warning, there is a huge amount of information available on the internet, but not all of it is properly researched. Beware!


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