Why did my blackberry jam come out red?

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I've done homemade jams countless times over the years, but this was my first with blackberries. The storebought varieties are dark, like the fruit; mine came out red. Still tastes good, but anyone know why the color change?

This was my guess as well. Red cabbage changes color pretty immediately when exposed to acids or bases. After shredding it, any fragments that end up in/around the sink tend to turn blue from whatever trace amounts of soap it comes into contact with.

An easy “test” for this jam would be to mix a drop of dish soap with whatever’s left of a plate/knife/etc. and see if it darkens.

I dunno, never measured it. Just as with other fruits, I just add a tablespoon of lemon or lime juice to the fruit, sugar, and (sometimes) pectin and it always comes out fine.

Adding lemon juice could definitely do it, but I've also noticed myself that the juice from frozen blackberries tends to be red as well. Maybe they're using another variety for the store-bought jams?