Are solid-state fermentation the answers to the challenges within New Food?

Hi there,

Recently I've seen solid-state fermentation come up here and there as a topic in discussions, but as well used by companies who wants to enhance flavours in plant based products. So from this I've dived into a rabbit hole leading to some interesting findings. 

A bit of background

A 100 years ago, solid state fermentation was as normal as liquid fermentation, but at some point, it was decided to pursuit liquid fermentation, and thus the last 100 years fermenters for that application have widely been developed and refined. However, with the challenges to bring down both capital investment, operational expenses and increase performance dramatically to get price parity it seems like a dead end to continue to pursuit the equipment predominately developed for pharmaceutical purposes which have the luxury of extremely high prices for their products and high switching costs.

Advantages with solid state fermenters

In a food environment cost is king, and here it makes senses to see what alternative advantages solid-state fermenters can bring. For fermentation processes, they have high titres, and a much simpler down stream process. Solid state fermentation uses significantly less water, which is an increasing challenge as fermenters become larger and larger.

But where it becomes really interesting is in substrate, where by-products such as fruit processing waste, straw, spend grains, coffee pulp, tea waste or even saw dust can be used. This means that it is possible to make a circular feeding stream where one industries waste is raw materials – often with very attractive prices as a side benefit.

Another aspect that I can't help to consider is how the cultivated meat process are struggling with the adherent nature of mammalian cells. And once the mammalian cells are grown, it is hard to make them form that network of fibres which gives the structure of a beef. I can't help but think that liquid fermentation is a dead-end. Might be that it makes sense to have a look at other technologies where fibres can grow, and which closer assembles the kind of technologies you are used to see in the meat industry.

A last advantage I want to point out is that for many of the fermentation processes, the low Aw value means that the risk of the organism being outcompeted is much lower. This means that rather than needing to sterilize everything to a log-9, 12 or even 16 it is often possible simply to boil the media prior to fermentation, which dramatically reduces the equipment cost as well as operational cost and overall equipment efficiency. 

So what are the challenges?

Needles to say oxygen transfer is not a challenge in solid-state fermentation, but that doesn't mean that the technology is without challenges. In my opinion the biggest challenge with solid state fermentation is that it is heavily underdeveloped. The most common types today are still tray type or drum type reactors even though they don't seem to be an ideal design.

Due to the underdeveloped nature of solid-state fermenters, there are often quite manual in their designs leading to higher OPEX costs. This also means that there is a general lack of sensors to measure biomass concentration, control pH, and adequate methods for controlling homogeneity and cooling rate as size increases. Many discusses that cooling is a problem, however as I see it is more of a problem of controlling humidity against evaporation rate where a new design is needed to be able to control humidity and evaporation rate independently.

Lastly there is the whole part of strain development. Though many of the popular organisms for liquid fermentation is also used in solid-state, optimizing organisms for solid state fermentation will likely mean that a new strain needs to be developed.

Conclusion

If you know anything about fermentation, I'm sure you are thinking that there is a lot of challenges here. That said, having an extensive experience in designing fermenters and hygienic equipment in general, many of these challenges are some which are doable in the hands of a skilled mechanical engineer. 

For the sensor part, I am generally in favour of measuring flux's rather than concentrations. If you measure oxygen consumption rate, metabolic heat, change in pH etc many of the kinetic models can compensate for a lot. As well, one of the key drivers for cost in many bioprocessing plants is the high aseptic level. Thus, the possibility to create a process with much simpler equipment, simpler downstream process and which in it's nature is more sustainable due to lower energy and water usage should at least deserve a proper assessment.

Sure there are challenges, but in my oppinion the rewards are equally interesting.