ARTICLE 40 F&A Alternative Proteins Edition April 2023 these gases as feedstocks opens up possibilities for creating more sustainable fermentation products, as they can each be produced using sustainable technologies or secured as secondary waste products of other processes. Each gas is already produced for or by other industries at orders of magnitude greater than that which would reasonably be required to service the production of product for the animal feed sector. To engage effectively with animal feed markets and make a material impact in a challenge as enormous as the sustainability of global human diets, scalability is vital. Fermentation systems are typically scalable in three dimensions, meaning that large-capacity production units can be built on a relatively small footprint. This is the opposite of traditional farming, which scales in two dimensions. As a result, expanding production capacity in traditional farming inevitably requires additional arable land, often associated with deforestation practices. However, not all fermentation systems are equal. Significant differences arise from the unique feedstock-feeding and product-harvesting regimes of each process. Submerged liquid fermentations are the most commonly used commercial systems, providing all the required nutrients for fermentation dissolved within a liquid broth. Gas fermentation is a subset of this type of fermentation, unique because the major carbon and energy source nutrients are added in gaseous form rather than pre-dissolved in liquid. The production rates achievable in submerged liquid systems are high due to the excellent availability of nutrient feedstocks throughout the liquid phase, where production ultimately occurs. This is crucial in achieving high production capacities from facilities with relatively small footprints. Scaling submerged liquid fermentation is largely a challenge of achieving as close to uniformity of internal conditions, such as nutrient availability and temperature, as possible in larger and larger vessels. Contrast this with photo-fermentations which use photosynthetic algae, another potentially good system for producing alternative proteins and other feed ingredients. The scaling of this technology is more challenging because light, the energy source for these fermentations, must be available throughout the production process. Because the substance inside these bioreactors is a relatively dense milky consistency, light does not penetrate well, so scaling cannot rely on bigger vessels. Maximising nutrient gas-to-liquid transfer in gas fermentation is a similar issue and arguably one of the most significant challenges to successfully scaling up the technology. However, getting bubbles to move through a milky broth is more straightforward than doing so with light. Several tweakable factors can be controlled and optimised to encourage the nutrient-containing gas bubbles to transfer faster into the liquid. OVERCOMING BARRIERS TO BROADER ADOPTION The animal feed sector is vast and continues to grow at pace alongside the rising demand for
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