The day before you want to cook your beans, rinse and pick over them to remove any bad beans or foreign objects - sometimes dried beans have a little stone or specks of dirt in the bag, and you don't want to crunch down on those later!
1 cup dried beans
Put the beans into a large bowl with the baking soda and cover with plenty of cold water. You need the water to come at least a couple of inches above the top of the beans so they have room to expand while soaking. Set aside to soak for at least 8 hours or overnight.
1/4 tsp baking soda, cold water
When you're ready to cook the beans, drain and rinse them, then put them into a wide, shallow pan and cover with fresh water. Don't cook the beans in the soaking water, you need to wash away the baking soda and any compounds that have leached out of the beans which can cause digestive issues.
Put the pan into your steam oven and set to Steam, 212°F/100°C, 100% humidity. Cook the beans until they can be easily squashed between two fingers. This could be as short as 45 minutes or as much as an hour and a half - it varies wildly depending on the variety and age of your beans. If you eat a bean and it's remotely grainy or chalky, it's not done yet. They should be creamy soft all the way through.
Remove the cooked beans from the oven and allow them to cool in their cooking water. Drain and use, or store them, in their liquid, in the fridge for up to 4 days or the freezer for up to 3 months.