How to make home made jam retain the fruity taste?

Most fresh fruits will lose their "sweet fresh flavor" when cooked. (*geeky stuff at end) When making jams, jellies etc., a good amount of sugar is added. This is done for a couple of reasons, the first is to combine with acid and pectin for thickening, the second is for flavor.

When making jam, the proportion of sugar to fruit will be somewhere between 40-100% by weight. (Jaggery is not as sweet as granulated sugar and you would want to add 1/4 to 1/2 more if you were using it in a recipe that called for sugar) Your jam didn't have anywhere near enough sweetener.

What you can do to retain the fruity flavor:

• For cooked jam, add more sweetener.
• Make a fresh fruit (raw) jam that isn't cooked, which will not require a lot of added sweetener

Fruit generally contain all 3 sugar types, the majority often being fructose.

From Wikipedia Fructose

The relative sweetness of fructose has been reported in the range of 1.2-1.8 times that of sucrose.[21][22][23][24] However, it is the 6-membered ring form of fructose that is sweeter; the 5-membered ring form tastes about the same as usual table sugar. Warming fructose leads to formation of the 5-membered ring form.[25] Therefore the relative sweetness decreases with increasing temperature.

Use a "low sugar" jelly/jam pectin, which balances the amount of pectin to reflect less added sugar, and then follow the directions for making freezer jam/jelly. Since it's preserved in the freezer, the fruit is added to the sugar/pectin/water after it gets taken off of heat, and is stirred for a minute. This results in minimal cooking of the fruit, and it retains a lot more fresh fruit character.

Along with balancing the sugar, I suggest a little lemon juice (or Vitamin C) to brighten/sharpen the fruit notes. This especially helps with very/borderline over-ripe fruit.
Good luck and good eating!

I recall making blackberry jam several years ago from berries that were quite smaller than usual, due to a unusual dry spell that year. The end result that the jam was noticeably stronger in taste and tasted far superior than I have ever had since. This might have been due the lower amount of fluid in the berries.

I generally pick my own berries, regardless of what species they are.

This jam lasted well over a year in good condition and never lost its' taste.