Bread tempeh french toast
This is part of our series on upcycling bread by-products. Kim originally contributed this recipe to Suveræne Svampe (lit. ‘Incredible Fungi’) by Lene Lange, a recent book which explores the role that fungi can play in human and planetary flourishing.
Table of Contents
i. Background
Rhizopus oligosporus is a filamentous fungus commonly used to ferment soybeans to make tempeh, a popular protein-rich food originally from Indonesia.
Here we grow this fungus on old bread, which is a great way to use up odds and ends of bread that you have dehydrated and saved over time. As R. oligosporus grows, the enzymes it produces break down the bread’s starches into sugars, whilst forming a mycelium matrix that preserves the bread's shape when it is eventually cooked.
Unlike traditional French toast, the recipe doesn’t contain any egg or dairy products.¹ Instead, we use the power of filamentous fungi to produce deliciously custardy, sweet and savoury flavours.
This bread isn’t mouldy in a conventional sense; it’s ready for frying. The white fluff is the mycelial network produced as R. oligosporus grows.
ii. Recipe
Ingredients
Sourdough bread, dried
Water, 150% weight of dried bread
Apple cider vinegar, splash
Rhizopus oligosporus tempeh spores, 0.2% by mass of the bread–water–vinegar mixture
Neutral oil
Toppings of choice
Method
Mix the water, apple cider vinegar and tempeh spores. The vinegar acidifies the substrate, allowing the tempeh spores to grow more easily and inhibiting the growth of other microbes.
Place the bread into a small plastic container with sides higher than the thickness of the bread, and pour the liquid mixture over the bread, flipping it over so that it fully absorbs the liquid. Cover the container with cling film and poke small holes in the top.
Incubate the inoculated bread at 30 C and 90% humidity for 24 hours.
Heat oil in a pan on medium-high heat. Add the bread tempeh and fry until golden brown on both sides.
Top with your desired toppings: we love it with berries, jam, maple syrup and butter.
iii. Adaptations
This recipe was tested on stale sourdough bread. You could try different types of bread, but we wouldn’t recommend using commercially produced sliced bread as this often contains antifungals and other artificial preservatives which can inhibit the growth of the tempeh spores.
The tempeh spores can be fermented for longer than 24 hours, though it can develop a stronger taste that isn’t for everyone. At the end of its growth cycle, after about 30-40 hours, depending on environmental conditions, it produces black spores, which can discolour the substrate.
Contributions & acknowledgements
Kim performed the original culinary R&D; he contributed this recipe to ‘Suveræne Svampe’ by Lene Lange. Aly reproduced Kim’s recipe and documented the process with additional notes, which Eliot used to help write the article following further discussions with Kim. Josh contributed editorial feedback. Aly photographed the final product in our food lab.
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Endnotes
[1] Though we do like to top it with butter!