• Wash, rinse and soak the soya beans overnight. Make sure the water is at least twice as high as the beans in the bowl.
• Drain the water and place the soya beans in a pressure cooker (you can use the stove pressure cooker or electric pressure cooker). Pour fresh water into the beans about 2 inches above the soya beans. Put the cooker lid on and start cooking according to the manufacturer’s manual. I use the stove pressure cooker and it took me around 30-40 minutes to cook.
• You can cook the beans by boiling them in a regular pot (if you do not have a pressure cooker). This way, it can take about 1- 1 ½ hour until the beans are fully cooked and rather soft.
• While the beans are cooking, prepare the ziplock bag by piercing all over the bag with a skewer or a toothpick at an inch apart. Set aside.
• Once the beans are cooked, take some of the skins that came off the beans and drain the water.
• Place the beans on a tray and leave them to slightly cool.
• When the beans feel warm to touch (around 30°-35°C/ 86°-95°F), add in the vinegar and stir well. Ensure all the beans are coated with vinegar.
• Then sprinkle the tempeh starter and mix well to make sure all the beans get the tempeh starter. 
• Spoon the soya beans into the prepared ziplock bag and zip the bag to seal.

Fermentation using a cooler bag:

• Get your cooler box, hot water bottle, and a stainless grilling rack ready. 
• Fill the hot water bottle with hot boiling water from the kettle. Place the bottle at the bottom of the cooler bag. Then put the grilling rack over the bottle and put the bag of soya beans on the rack. Cover the cooler bag with its lid.
• After 24 hours, open the bag and take the hot water bottle out. Change the water from the bottle with fresh hot boiling water and put it back underneath the grilling rack in the cooler bag. Put the lid on the cooler bag and leave the tempeh to ferment further. 
• Your tempeh should be ready after 48 hours. 

Using the oven:

• Put the bag of your soya bean on the middle rack of your oven and leave the oven light on for 12 hours and take it out and leave it in a warm place (in summer). During wintertime, you can leave it in the oven with the light on for 48 hours. 

Using the airing cupboard:

• If you have an airing cupboard over your heating boiler, you can leave the bag of the soya beans to ferment in that cupboard. Although I have never done this (because I don’t have an airing cupboard anymore), I know people who use this method and it works all the time.