Whisk the barley malt powder into 2 liters of warm water (50C / 122F) in a large bowl. Let it sit for 15 minutes, stirring once, so the enzymes activate.

Strain the cloudy liquid through a cheesecloth-lined fine-mesh strainer into another bowl, squeezing the solids firmly to get out as much milky malt water as you can. Discard the spent grain.

Rinse the sweet rice until the water runs mostly clear. Cook it with 600 ml water in a rice cooker or covered pot over low heat for 20 minutes, until soft and stickier than usual steamed rice.

Transfer the hot rice into a rice cooker bowl or heatproof pot and pour in the strained malt water. Stir well to combine.

Hold the mixture at 60C / 140F for 4 hours, using the rice cooker's keep-warm setting or a very low oven with the door cracked open. At the 3-hour mark, taste it, the liquid should be distinctly sweet and watery, a sign the starch has converted to sugar.

Strain the fermented mixture through a cheesecloth-lined strainer into a 6-quart / 5.7 L stockpot, pressing hard on the solids to squeeze out every bit of sweet liquid. Discard the rice pulp.

Bring the liquid to a boil over medium-high heat, skimming off any foam. Add the salt if using, reduce to medium, and simmer uncovered for 2 to 2.5 hours, stirring every 10 minutes.

In the last 30 minutes, the syrup thickens and darkens to deep amber. Stir constantly here, it scorches fast once most of the water is gone, and a burnt pot means starting over.

Cook until a candy thermometer reads 113C / 235F and the syrup falls off the spoon in a slow, thick ribbon rather than a thin stream. This is the firm, chewy stage for pull taffy.

Pour the hot syrup onto an oiled sheet pan (33 x 46 cm / 13 x 18 inch) or a silicone mat. Let it cool for 10 to 15 minutes, until warm but safe to handle.

Oil your hands lightly, or dust them with roasted soybean powder. Gather the taffy and pull and fold it back on itself for 5 to 8 minutes, until the color lightens from dark amber to pale gold with a satiny sheen.

Roll the pulled taffy into a rope about 2.5 cm / 1 inch thick. Snip into bite-size pieces with kitchen scissors dusted in soybean powder, then roll each piece in the remaining powder so they don't stick together.

Let the pieces firm up at room temperature for 30 minutes before serving or storing.