Preserving Tomatoes: A Primer

Learn the basics of water bath canning tomatoes, and store your crop with these simple recipes for canning tomatoes and oven-drying them.

| Summer 2017

Tomatoes are one of the first foods that many people try to can, partly because water bath canning tomatoes is relatively easy. However, gone are the days when you could simply smash some raw tomatoes into a canning jar, process them in a boiling water bath for a while, and call it done. To can modern tomato cultivars safely in a boiling water bath, you may need to add some acidity. Here’s why.

Over the past several decades, many tomato cultivars have been bred for sweetness. Old-fashioned tomatoes had enough natural acidity that you could safely can them without any other ingredients, but many of today’s tomato cultivars require added acid to bring their pH low enough for canning. Some heirloom tomato cultivars may technically be OK to can without adding acid; however, it’s better to be safe.

Adding acidity. Per pint jar of tomatoes, add 1 tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid. For quart jars, double those amounts. I don’t really notice a difference in the taste, but if you’re worried that it might be too sour, you can add a little sugar to offset the added acidity. Use bottled lemon juice. I know, I know — fresh citrus juice always tastes better, and that's what I use for regular cooking. But in this case, it’s not about flavor — it’s about food safety, and bottled lemon juice has a consistent level of acidity that fresh lemons don’t always have.

You may come across old instructions for canning pasta sauces and other tomato-based products that say tomatoes may be safely canned in a boiling bath due to their acidity. But, again, this is no longer considered safe.

Raw Pack Tomatoes and Hot Pack Tomatoes

To raw pack tomatoes, you simply crush chopped-up raw tomatoes, put them into clean jars, add acid (and sometimes hot water), and then process them in a boiling water bath. It's certainly the easiest way to can tomatoes, but it's also my least favorite. The disadvantages of the raw pack method are longer processing times and a watery product that tends to separate after it cools in the jars (the red pulp floats unattractively above a layer of almost clear, yellowish liquid). But if you really need to get your tomato-canning project done in a hurry, raw pack is better than not canning any tomatoes at all. Despite the longer processing time, it’s still slightly quicker upfront than the other methods.

To hot pack tomatoes, you boil or roast tomatoes for a few minutes before canning. Also, hot pack is almost as easy as raw pack and results in a less watery product that doesn’t separate as much.

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