I've been working on up-scaling my tempeh production and thought I'd share my progress. I found a 5l glass / pyrex dish with fitted plastic lid that I am using to hold the tempeh as it ferments. I drilled small holes all over the plastic lid to provide air flow; the sides and bottom are fully contained by the glass but this does not seem to be an issue. I am fortunate to currently live in a country (Malawi) that has a climate warm enough to provide the fermentation temperature, so I no longer have to use an incubator system to keep it warm.
In fact the biggest problem I have is keeping it cool! After around 18hrs, the heat produced by the fermentation / mycelium rockets and I've recorded it at 45 degC / 115 degF. This resulted in patches of underdeveloped Tempeh in the centre of the block, presumably where the most heat is being concentrated. I've managed to get around this by placing the glass container on a wire cooling rack within a water bath. The water comes up ~2/3 the side of the glass dish, and although the water temperature does raise slightly it holds pretty close to the ambient room temperature. There is no fan or water pump at the moment. As you can see from the attached pictures, the top of the block is now beautifully uniform and consistent after 24hr ferment time. The underside view is slightly underdeveloped, next time I will try letting it ferment a little longer. However the 6x 330g blocks I get from the whole slab are all sturdy and have mycelium growth throughout.
I've found that keeping the beans on the firm side when I cook them is preferable to having them get too soft, as they tend to turn mushy when mixing in the starter powder and the slab collapses somewhat under its own weight, preventing airflow throughout the beans.
This is my full process:
- Cover 1kg dried soy beans with ~4l boiling water, and leave to soak overnight
- In the morning, drain off the soak water and replace with fresh water. Massage beans with hands to remove the hulls. Float off the hulls. I try and limit this step to 15-20mins max, any more sees limited improvement for the time spent.
- Place soaked, dehulled beans into pressure cooker, cover with fresh boiling water and cook. I use a 6l Instant Pot (IP) and 1kg beans plus water is pushing the capacity limit of the IP - I keep the water level below the 2/3 limit line, otherwise I've found the seal / pressure weight can fail and it struggles to get to pressure and makes a big mess! I cook for 9 minutes high pressure, then leave to do a full natural release which can take 45min - 1hr. I've found trying to do a manual pressure release takes at least 15 minutes and is very messy, simpler to cook for less time (at pressure) and let it cool on its own.
- Drain the beans, then place in a large baking tray lined with a tea towel. Place in a warm sunny spot to air / sun dry. I stir 2-3 times to help dry all the beans equally. I dry them until they lose the moisture sheen.
- Stir 2 tbsp apple cider vinegar into the beans, followed by a mix of 3tbps rice flour and 1.5 tsp starter powder (rhizopus oligosporus). I find doing this in a large saucepan or other round container makes this easier.
- Pour cooked, dried and inoculated beans into the glass container, and smooth over with downward pressure to make a consistent level slab. Cover with the plastic lid, drilled with holes. Cover with some form of mosquito netting to keep out flies and any other pests!
- After ~ 18hrs, place glass container into a water bath, raised up on a cooling rack so the water can reach fully underneath the glass container. Regulate water temperature with ice cubes if necessary. Ready after ~24hrs full ferment time, ambient room temperature ~30 degC / 86 degF.
- Split into 6 equal blocks, and refrigerate / freeze in tupperwear as required.
Next improvement ideas to try are a longer fermentation time (I've been reluctant to push too far as 24hrs fits in with my schedule, and I don't want to loose a full batch!), and to try an enclosed water bath with some form of water / air circulation.
