Beach plum jam is a delightful seasonal treat in coastal New England where native beach plums (prunus Maritima) thrive. Learn how to turn these tiny slightly sweet-slightly tart plums into jam to preserve their unique flavor and enjoy it throughout the year.
- Wash thoroughly and pick through the beach plums to remove any leaves and stems.
- Add the beach plums and water to a large pot and bring them to a boil. Cook the fruit until the skins break open and the fruit softens, for about 10 minutes.
- Using a potato masher mash the plums to break them down even further and help release the flesh from the plum stones (seeds).
- Place a large colander over a large bowl and using a 1 or 2 cup liquid measuring cup, scoop the fruit mash into the colander in batches. Use a rubber spatula, the back of a spoon, or a flexible bowl scraper to press the fruit mash through the colander and into the bowl, leaving the plum skins and stones behind. Discard the skins and stones and repeat the process in batches.
- Rinse out the pot if any plum skins or stones were left behind. Place the pot on a kitchen scale and zero out the scale then return the strained fruit mash back to the pot and record the weight of the fruit mash. You will need this weight to calculate the amount of sugar and lemon juice to add. If you started with 3.5 kg or 8 lbs of beach plums then you should end up with about 2140g or 4 lbs 11 oz of fruit mash.
- As a general rule jam requires anywhere from 50%-100% sugar by weight of fruit. Beach plums can be quite tart so 75% sugar to fruit or a 4:3 ratio of fruit to sugar works well to balance out the tartness of the fruit. Multiply the weight of the strained fruit mash by 0.75 to figure out the amount of sugar to add. You can adjust the percentage from anywhere from 50% to 100% of sugar to fruit mash as a matter of preference. For this batch, we need 1605 g or 3.5 lbs of sugar. Add the sugar to the pot.
- For every 1000 g of strained fruit mash, you’ll need 30 g of lemon juice. In other words, 3% lemon juice by weight of strained fruit mash. Multiply the weight of the strained fruit mash by 0.03 to figure out the amount of lemon juice to add. Add the lemon juice to the pot.
- Add the cinnamon sticks to the pot. Cut the orange in half and squeeze the juice into the pot then add the orange rinds as well. If the orange is seeded remove seeds first or squeeze the fruit over a strainer to catch the seeds. If using a whole vanilla bean, it can be split with a knife and added now. If using vanilla extract add it after the jam is cooked down.
- Stir to dissolve the sugar as you bring the mixture to a low boil. Cook the mixture until it sets, stirring occasionally. To check if the jam has been set, chill a small dish or ramekin in the refrigerator or freezer while the jam is cooking. Spoon some of the jam onto the chilled dish and let it sit for a minute. If the spoonful of jam sets up to the consistency of jam, where it is thick and coats the spoon, then the batch is ready to can. If it is still runny, continue cooking the jam, and retest it every 10 minutes or so until it sets up. For our example batch, it will take roughly 30-40 minutes until it sets. Generally, smaller batches will take less time and large batches will take longer to cook.
- While the jam is cooking sterilize the jars and lids. There are a few ways to do this, but I like to place the jars into my canning pot and fill it enough to cover the jars with hot water then bring it to a boil and let it simmer until the jam is ready. Remove the jars cautiously with canning tongs. To sterilize the lids put them into a strainer and submerge them into the boiling water for 1 minute.
- Fill the sterilized jars with the jam leaving 1/2″ of headspace. A funnel is very handy for this step. Clean off any drips around the mouth of the jars with a damp clean cloth or paper towel. Place the lids on the jars followed by the lid rings and seal the rings to just finger tight. Do not tighten the lids too much or the air will not be able to escape as the pressure builds up while canning them.
- Place the filled jars back into the hot water bath and bring the water back to a rolling boil. Cover the pot with the lid cracked and boil the jars for 10 minutes.
- Use canning tongs to carefully remove the jars from the hot water bath and let them sit to cool to room temperature. The jars will make a “pop” sound as they seal and the lids will depress. Once this happens remove the rings and dry any water drops on the jar lids with a towel.
- Label the jars with the date and store them at room temperature out of the sun for up to 1 year. Opened jars will need to be refrigerated and will keep for 2 weeks.
- You can use any type of plum for this recipe instead of beach plums.
Keywords: beach plum, plum