Starch gelatinization is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water. Starch begins to gelatinize between 60C and 70C, the exact temperature depends on the specific starch. For example, different starches exhibit different granular densities, which affect the ease with which these granules can absorb water.
- Add all dough ingredients, except butter, in a mixing bowl fixed with a dough hook and beat at slow speed for 1 minute. Switch to the medium speed, and continue to beat for 3 minutes until a dough forms. Cut in butter gradually and mix for approx. 5 minutes until gluten is fully developed, i. e. elastic, smooth, non-sticky and leaves from sides of mixing bowl.
- Place the dough in a lightly greased mixing bowl. Cover and let rise until doubled in volume, about 1 hour. Turn dough out onto a lightly floured surface and gently punch down the dough to expel the air. Let rest for 15 minutes. Roll and shape the dough into 30cmx40cm rectangle to fit the baking tray. Cover and let rise in warm place for 40 minutes.
- Preheat the oven to 175C/350F. Combine pork floss and seaweed crumbs. Use the tines of a fork to prick the top of dough, then brush with egg wash. Sprinkle with chopped onions and sesame seeds and bake for about 15 minutes.
- Gently invert the bread on a parchment paper. Thinly spread with mayonnaise and cut a few slits at one edge of the bread. Be careful to cut the slits half-way through the bread only. This increases the flexibility of bread roll-up. Sprinkle with the pork floss mixture and roll up while still warm. Cut the bread into the sections to your desired length after 30 minutes. Spread the cutting sides with some mayonnaise and pork floss.