When I first started out I decided to consult the experts and I asked for advice from two of my favorite jam-making pros: my aunt, Becky Courchesne of Frog Hollow Farm, and my friend, Pim Techamuanvivit of the food/travel blog Chez Pim. I also referred to Christine Ferber's book Mes Confitures. The recipe below was inspired by their advice.
This is a french-style jam that is looser than many commercial jam varieties. There is no added pectin. It has a wonderful fresh strawberry flavor with not too much - but not too little - sugar.
It is always best to make jam in small batches. If you by one flat of strawberries at the market eat a basket or two right away, clean and freeze a few baskets worth, and use the rest of the baskets (about 6) for jam making. This is a two-day process but there is very little actually cooking time. Cleaning the berries and washing the jam jars will likely be the most time consuming part.
5 lbs strawberries -- this is about 6 or 7 baskets of strawberries
3 lbs sugar*
1/4 cup lemon juice
*Pim explained to me that good rule of thumb is 60-65% sugar to the weight of whole fruits. While you might be tempted to use less sugar this is not a good idea because the fruit may not preserve properly. That said, homemade strawberry jam is very safe.
1) Rinse and dry strawberries in batches. I use a salad spinner. Remove green leaves and stem on top of berries (this is called hulling). Cut berries into large pieces. Place berries into a large glass or ceramic bowl. Add the sugar and lemon juice and mix to coat. Cover with plastic wrap and store in the fridge overnight. This is called macerating. The sugar will cause the strawberries to release their liquid.
2) The next day get your jars and lids ready. I use the 2-piece lids (with lid insert and lid ring) so that I can reuse my jars, only replacing the inexpensive lid insert each time. Wash jars and lid rings in warm soapy water. Place on a baking sheet and put into a 250F oven for at least 20 minutes. Leave them in the oven until the jam is ready to be jarred. While your jars and lid rings are in the oven put your lid inserts in a pan of simmering water for about 10 minutes. Leave them in there until you are ready to fill your jars.
3) On the stove-top pour strawberry mixture into a large, heavy nonreactive pot. I use a Le Crueset soup pot. Bring the mixture to a boil and cook for 10 minutes. Pour entire contents of pot back into your glass or ceramic bowl.
4) Place a colander in your cooking pot and pour in strawberry mixture. Remove colander with berries and and bring syrup to a boil. Cook the syrup on high heat, regularily scraping the bottom of the pot with a wooden spoon or spatula to make sure nothing is sticking, until the syrup reaches 221F. If you don't have a thermometer you can simply cook the syrup until it reduces by about half and looks dark and sticky.
5) Add the berries back into the pot and continue to cook over high heat for just a few minutes. You want to make sure the berries are cooked through and hot -- but you don't want a burned layer at the bottom of the pot. Once the jam has cooled just a bit skim off any foam from the top, if you like.
6) Remove the jars from the oven and fill the hot jars with your hot jam (leaving about 1/4 in. of headspace) and cover with hot lids. This ensures a tight seal. Place jars back on baking sheet and back into the oven at 250F for 15 minutes. Remove from oven and let jars cool completely. You will hear popping noises as jars seal. If any jars do not seal after a few hours simply store them in the fridge and use the jam in the next week or so. All sealed jars should be stored away from light and heat. They last for years unopened and a week or so once opened and stored in the fridge. Enjoy!