I’m very used to making jams, jellies, chutneys, ketchups and pickles, all of which require basic sterilisation of jars, easy recipes and a straightforward process to fill and seal the jars. In these recipes boiling helps kill harmful bacteria and yeasts as well as reducing the moisture in which they thrive; sugar or acid stops regrowth and sealing in a sterilised airtight jar prevents recontamination.

But these techniques aren’t suitable for low acid foods such as fish and meat which is why we often turn to other techniques to extend their shelf life. The same goes for vegetables, when we want to preserve them without introducing the strong acidic flavours of a pickle.

Most commonly for fish and meat here in the UK, we freeze, cure or dry them.

Freezing turns moisture into ice and also inhibits the growth of most bacteria. The advantage is that the fish or meat is as fresh once it’s been defrosted. Curing with salt, sugar, nitrates or nitrites works by drawing out moisture. It changes the nature and flavours of the fish or meat, but this is often highly desirable – many of us adore cured salmon, bacon and cured hams such as Parma and Serrano. Drying, by sun, in a dehydrator or oven, or by smoking, works on a similar basis of reducing moisture. It also seals the surface of the fish or meat, which makes it difficult for bacteria to enter. Smoked fish such as salmon and mackerel are popular in the UK. Biltong, Bresaola and jerky are examples from the dried meats category.

I do know people who cure and smoke fish and meats at home. But it’s relatively rare.

Preserving by fermentation is becoming more popular here too, though it is still uncommon. As the food ferments, it produces lactic or other acids, which are themselves preserving agents. Kimchi (which is enjoying a surge of popularity amongst foodies at the moment), sauerkraut and surströmming (which my dad enjoys but I just can’t get into) are all examples of preservation by fermentation.

Of these three methods, freezing is probably the easiest for the home cook. Indeed, our freezer is full of raw home grown vegetables as well as raw meat and fish and portions of cooked food such as stews and curries.

There is another way of preserving low acid foods so that they can be stored at ambient temperatures and retain their essential flavours or textures. Known as canning, the process was first trialled by the French navy in the early 1800s, after they launched a competition seeking new methods of preserving food. Although the method was originally tested and developed using jars, when the process took off commercially, most food was preserved in tin cans rather than glass and hence the process became known as canning.

After the food is prepared and sealed in to the tin (or glass jar), a heat and pressure treatment is applied to the container to kill the bacteria within. It’s the heat, not the pressure, which destroys bacteria, but pressure provides the easiest method to achieve sufficiently high temperatures. It’s important to be thorough here, as there is no acid, sugar or salt added to the ingredients to restrict the growth of any bacteria that survives the treatment.

Canning as a commercial process took off around the world, nowhere more quickly than in the US, as did its counterpart, home canning. Indeed, judging by online content, I consider America to be the spiritual centre of home canning! Many of the other preservation methods are more popular in Europe and elsewhere in the world, but it seems to me that the Americans have taken the canning process to heart.

It’s critical to reach the correct temperature and to maintain it for a sufficient duration, which can be quite a challenge for the home cook. To that end, there are home pressure canners available, though in the UK we have access to a smaller selection, at higher prices.

Because of the risk of botulism, the toxins of which are not detectable by taste or smell, the United States Department of Agriculture (USDA) provides detailed guidelines for home canning. Botulinum spores are very hard to destroy at 100°C but can be eliminated at 120°C, provided the temperature is maintained for long enough. Where foods do contain enough acid, the guidelines suggest a boiling water bath will be sufficient. For lower acid foods, a pressure canner to reach the higher temperatures is recommended.

As an avid food blog reader, I’ve been bookmarking home canning recipes for several years.

Attending an event by Le Parfait, when they launched their products into the UK last year, gave me the last push to give this form of preserving a go myself, especially when they kindly provided some sample jars for me to use.

In the US, Ball or Kerr brand Mason jars are the most popular, featuring a two part lid – a flat disc cap that seals to the rim of the jar and a screw on band which secures the disc cap into place until the canning treatment creates a vacuum seal. Here in the UK, we’ve traditionally used hinged clip top jars with rubber sealing rings such as those made by Kilner. Indeed, like Hoover vacuum cleaners, “kilner” seems to have become shorthand for describing this style of jar regardless of manufacturer. Le Parfait is a French brand and has been going for over 80 years. They offer both styles of jar – their Super Preserve and Super Terrine both have clip top lids and their Familia Wiss have seal caps under screw-on lids.

As far as I can see, the advantage of the clip top design is that, once purchased, the costs are minimal. The rubber sealing ring lasts well, though not indefinitely, and needs replacing from time to time. That said, I find them more difficult to open and close, and awkward to sterilise, since I use the oven method for jars and boil the lids separately. The Mason style jars are much easier to use but since the disc caps are single use only, the costs of using them are higher.

At the moment, I don’t have a pressure cooker or pressure canner, so I’m using a large and ancient Indian aluminium stockpot. I mentally refer to it as a cauldron, though that does give a slightly wiccan air to it. I also don’t have a canning rack – essentially a special wire metal basket and handle which makes lowering and lifting jars from the water much simpler; it also keeps the jars from sitting directly on the base of the pan, touching the sides or rattling against each other. In my cauldron, I use several flannels and tea towels to line the pan and separate my jars and I’ve not yet discovered an easy way of lowering the jars into boiling water!

Without pressure, I can’t achieve temperatures above 100°C, so am hesitant to use the technique for fish or meat products.

Stay tuned for my first canning experiments.

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