Here is an old recipe from pre-pectin days.
OLD FASHIONED STRAWBERRY JAM
8 cups strawberries, chopped
6 cups sugar
Lemon juice (optional)
• Sterilize the jars.
• Rinse the berries and drain well.
• Remove the hulls.
• Chop the berries. Don’t puree them.
• Measure berries into a large, heavy-bottomed saucepan.
• If fruit is very ripe add 1 Tbsp lemon juice for every cup of berries.
• Place the fruit and sugar on medium heat and bring to simmer.
• Increase the heat to quick boil.
• Boil rapidly for 10-5 minutes stirring constantly to prevent burning.
• Remove from heat and skim off any foam.
• Place the lids in very hot water to soften the rubber.
• Place a wide-mouthed funnel over a sterilized jam jar.
• Ladle the hot jam into the jar leaving a 1/4 inch headspace.
• Use a damp (not wet) paper towel to wipe the rims.
• Place the prepared lids on the top and screw on the cap.
• Place the jars filled with jam in the oven and process at 212F for 2 hrs.
• Store jams in a dry, cool place.
In terms of food safety, oven processing fruit and fruit jams is no more risky than the hot water bath method. The reason for that is simple. No open cattle will reach above the boiling point of 100°C or 212°F. Keep in mind though that low acid or non-acid foods should never be processed by any other than the pressure canner method. However oven processed fruits and fruit jams are as safe as those processed in the hot water bath.
