Summer Blueberry Jam
from https://www.seriouseats.com/

This delicious blueberry jam made from in-season summer blueberries, sugar, and lemon juice couldn't be more simple to make. The key is to select the best berries: Namely, a mixture that includes mostly just-ripe berries with a few under-ripe berries as well. By selecting berries that aren't too ripe, you'll get more pectin, acidity, and tannins in the batch, which results in jam with a better, jellied texture and richer, more complex flavor. Avoiding very ripe fruit will prevent jam with an overcooked taste and leathery texture.

One reviewer said: "I had never made jam without pectin before. In fact, I've only made jam one other time and that was 2 years ago. It was good, but a bit too firm. This recipe gave me more control over the destiny of my blueberry jam! And the flavor is so much better than pectin jam. I made 1/2 recipe to test it out and the next day made a full batch. This is the only way I will make blueberry jam again!"

Note: It's generally recommended to add lemon juice to blueberries when making jam, and there are several reasons why. Lemon juice helps to:

• Lower the pH level: This is crucial for safe canning as it helps prevent the growth of harmful bacteria and allows for a shorter water bath canning time.
• Enhance flavor: Lemon juice adds a bright, tangy flavor that complements the sweetness of the blueberries.
• Activate pectin: Blueberries have a lower natural pectin content, and adding lemon juice helps to activate the pectin, which is essential for thickening the jam and achieving the desired consistency.
• Preserve color: Lemon juice also helps to prevent the jam from becoming dull or discolored over time.

3 pounds, 8 ounces blueberries, preferably small, mostly just-ripe berries with some under-ripe berries as well
1 pound, 12 ounces sugar
1/4 cup fresh juice from 2 whole lemons

Mix everything together in a large mixing bowl and scrape into a large pot or jam-making vessel.

Cook berries on medium-high heat, stirring very frequently, until blueberries have released enough liquid to dissolve the sugar, about 8 minutes. Increase heat to high and cook, stirring just enough to prevent scorching on bottom of pot, until berries are foamy, about 10 minutes. Continue to cook, stirring more frequently and lowering temperature as foam begins to subside, 10 to 20 minutes longer. Cook until most of the fruit is disintegrated and bubbles have slowed down and become glossy, about 10 more minutes (times can vary depending on fruit).

Test for doneness: Turn off heat and set a small spoonful of jam in the freezer for 5 minutes. Jam is done once it holds together and doesn't run off the spoon when tilted; if jam is too runny, return to low heat and continue to cook, stirring frequently and repeating doneness test every 5 minutes, until jam passes test. Eat right away, or can following your canning equipment instructions. Canned jams can be stored in a cool, dark place for up to 1 year.

Makes 12 jars (she doesn't say what size - from the picture it looks like the small jelly jars)

Reviewers reported lower yeilds:

- I halved the recipe, expecting to get 6 half-pint jars, but only ended up with three plus a little extra.
- The yield seemed high to me from the get go. From 1 1/2 batches (8 pints of blueberries, ~5 1/2 lbs), I ended up with 10 half-pint jars. That is right in line with what I expected.