Just recently I have made 6 batches of Mango Jam. All turned very dark brown while cooking and are almost black when jarred but they taste great. What is the reason for the color change?
Fruit color change
fruitjam
Related Solutions
Were your blueberries grainy? I occasionally get a pint that have a grainy texture. I've heard that this means they aren't quite fresh, but they usually taste just fine despite the texture. I'm not sure if this particular graininess translates to a jam though.
Jam can also get grainy from sugar that isn't fully dissolved. This can happen more easily with larger batches, since the fruit can start to boil before the sugar is fully dissolved.
For your particular recipe, perhaps a more thorough stirring after adding the sugar would help. You should be able to turn the heat down once you add the sugar so that you can stir it thoroughly before going back to high heat to boil for that 1 minute.
You just need to work out your forearms more. :)
If food gets on the rim of the jar it can greatly add to the friction after the lid is on. It actually makes the whole process unreliable- the food might prevent a seal from forming or it might harden and make the lid difficult to remove- either way make sure the rim of the jar is clean.
Canning jars create a vacuum when the heated air in the jar contracts. This vacuum is what holds the lid on tightly. You can alter the strength of the vacuum in two ways:
1- leave more air at the top of the jar (called headspace).
More air means that a smaller percentage of the air will be forced out and the seal will be weaker. Be careful that you don't make it too weak. If the seal fails the food will spoil.
Jam recipes meant for normal canning jars will include the recommended headspace. You should start there with your experiments.
2- Let the jam cool a little before applying the lid.
This will also result in less air being forced out and a weaker seal. This is something you can experiment with but it would be more finicky than #1. If you do try it, watch your jars closely for a while and put them in the fridge if the seal fails.
The canning process for jam in normal canning jars usually includes boiling the jars afterwards to ensure the jars seal properly. With those lids, sealing too strongly isn't a concern as the lids are disposable. Even with your jars, you want a very strong seal. If you are having trouble opening them perhaps you should try using a tool that will give you leverage but not damage the lid.
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Best Answer
I reckon it could be due to oxidation of fruits.
It's very common once you leave fruits that are cooked/uncooked in the open air. It probably helps if you could add a little salt in there ( even though it may seems weird, but it definitely works).
The reason why factory made jam does not turn dark at all is because of all the additional food addictive and preservative that is inside the food. I honestly, do not recommend keeping fresh mango jam for too long because it does go bad very quickly.
It happens to a lot of other food stuffs like potato etc.