Wash the apples carefully, since the peel will be used too.
If you use a peeler you can peel the apples easily. For a small amount of apples, a knife is fine.
Cut the apples (700 g) into 8 pieces (or smaller). Cut the cores into half, and remove the stem and bottom end bits.
Put the peel and core (totaling about 400g), 1/2 a lemon worth of juice and 800 ml of water in a pan, and simmer over high heat for about 30 minutes. Stir occasionally with a wooden spatula.
When the cores have fallen apart and the spatula feels heavy, strain the contents of the pan through a piece of clean muslin (or cheesecloth) to extract the pectin liquid.
Add the fruit and 1/2 a lemon worth of juice to the pectin liquid (which should be about 500 g), and simmer over high-medium heat while stirring with a wooden spatula.
When the mixture has been reduced by about 2/3, add the sugar in 3 batches 5 minutes apart. If you want the jam to have a longer shelf life, increase the amount of sugar to 500 to 600 g.
When simmering the jam, try not to stir it up too much. Shake the pan instead while trying not to crush the fruit for a preserves-type jam.
The result is a subtly sweet, pretty apple jam with pink colored jelly surrounding the fruit.
Since this recipe only uses a small amount of sugar, it's not suited to keep for a long time. After Step 3, take out the cores and peel, and store the jam in the freezer.
Story Behind this Recipe
Usually apple jam is made by covering the fruit with sugar to draw out the moisture before simmering. I used to use this method, but the color never turned out as nice as I wanted. I thought it was kind of like making caramel from sugar syrup. So I added a creative step.
The season for Kougyoku apples is short, and making a large amount of homemade jam is a big job. So I divide the apples into the peel + cores and fruit, add lemon water (1/2 a lemon worth of juice or a little salt added to 1 liter of water) to both, pack into plastic bags and freeze. They keep for at least 10 months (from my experience).