Sunday, May 4, 2008

Canning excess produce for winter

The first frost arrived early this year, and the nights are chilly. Thankfully, I have managed to can at least some excess produce (I will have to plant even more next year!). We are well stocked with canned tomatoes and beans, capsicums, apples, plums, cherries and peaches, as well as a number of pumpkins which I store whole in a cool room in the house. I had also canned some jars with carrots, but they got eaten very quickly!

This has been my second year of "serious" canning. I started last year with tomatoes and various kinds of fruit, but this year I really wanted to find out how to preserve low acid vegetables without having to resort to using a freezer.

It turned out to be easier than I thought, however, care does need to be taken.

I am fascinated by the different approaches taken by different cultures. In summary, there are three different ways of canning vegetables: using a vinegar-water solution with at least 50 per cent vinegar (recommended by Australia's Fowler Vacola bottling company), boiling vegetables in a water bath for very long periods of time (recommended by Germany's Weck bottling company) or using a pressure cooker capable of reaching more than 120 degrees Celsius to kill off all dangerous pathogens, including all spores of clostridium botulinum which can cause life-threatening botulism (as recommended by US food authorities).

Personally, I don't particularly like vinegar-water solutions and only use those where unavoidable (such as for capsicums which don't survive pressure cooking or long cooking times). The long cooking times for boiling water bath preserving (which range from 90 to 120 minutes depending on the variety of vegetable) seem rather energy intensive - I only use the water bath method for fruit and tomatoes which can much quicker. The ideal method for all other low acid vegetables is using a pressure canner.

In Australia, it is difficult and quite expensive to buy pressure canners, which are not produced here and have to be imported from the US. The Australian company Fowler's Vacola, which is the household name for jars, rings and lids in this country, only offers boiling water canners.

After looking into the issue at great length and agonising over whether it would be worthwhile to spend hundreds of dollars on a pressure canner that I might only use a few times a year, I finally realised that it is actually not necessary to use a purpose-built pressure canner.

A pressure cooker that is big enough (at least 10 litres) and capable of reaching a high pressure of 14 psi (over 120 degree Celsius) will do the job nicely and safely. However, care needs to be taken to choose the right kind of pressure cooker, as some of the cheaper imports will not reach sufficient pressure. I ended up getting a Fagor Duo pressure cooker (and there are a couple of other good quality brands which will do the job, too), and I am very happy with my choice.

My pressure cooker, which came with a small canning rack, is big enough to can three 1-litre jars or a slightly larger number of smaller/skinnier jars. This is perfect for me, as it allows me to do the canning "as I go along" rather than trying to do everything in one big canning session. And on days when I don't do any canning, I use the pressure cooker for cooking.

Pressure canning times vary but many low acid vegetables can be canned safely in 25-30 minutes. A complete table of pressure cooking times is regularly published by the US Department of Agriculture

When using an "ordinary" pressure cooker for canning, it is important to let the pressure drop naturally, as the jars are also under pressure and a seal will not be made if the pressure drops too rapidly (such as when using the "quick release" button).

*Note: US advice generally says that pressure cooking is the ONLY safe way of preserving low acid food. The German canning research company Weck, on the other hand, does not recommend pressure cooking and instead believes vegetables should be canned for up to two hours in a boiling water bath. However, when I checked why Weck does not recommend pressure canning, it turned out that they were concerned people would be too impatient or forgetful and might use the quick pressure release button, resulting in failure.