Whisk the malted barley powder into the warm water. Let it sit 20 minutes, stirring once or twice, so the starch-digesting enzymes release into the water.

Strain the mixture through a fine sieve lined with cheesecloth, or an ordinary clean dish towel, squeezing firmly to push out as much cloudy liquid as possible. Discard the coarse bran left behind. This liquid is your malt water.

Pour the malt water into the rice cooker insert along with the cooked rice.

Set the rice cooker to its keep-warm function, not the cook setting, and leave the lid propped very slightly open with a chopstick. Let it sit 4 to 6 hours.

Check it after 4 hours: the liquid should taste distinctly, unmistakably sweet, and a few grains of rice should be floating on the surface rather than sitting on the bottom. If it still tastes mostly like water, give it another hour.

Scoop out about 1/2 cup of the floating rice grains and set them aside in a bowl of cold water. Pour the rest of the liquid into a saucepan, leaving the remaining softened rice behind or straining it out.

Add the sugar and sliced ginger to the saucepan. Bring to a boil, skimming off any foam, then simmer 5 minutes.

Cool the liquid completely, then refrigerate until cold. Serve in cups or bowls with a few of the reserved floating rice grains and pine nuts on top.