Start with a boundary, not a slogan
“Energy in, protein out” sounds like one calculation. It is really a chain of calculations. For a crop, the inputs include fuel, fertiliser manufacture, field operations and processing. For fermentation, they include feedstock production, electricity, heating, cooling and separation. For livestock, they include feed production, animal metabolism, housing and manure management.
A useful comparison chooses the same boundary for each route and asks how much edible protein leaves it. The protein has to be measured at the point people can use it, not at the easiest point for a company to report.
Efficiency is not one thing
An organism can be efficient at turning a feed into biomass while the whole factory remains energy-intensive. A fermentation process may have a high yield in its vessel but need substantial energy to make feedstock or purify the ingredient. A farm can improve feed conversion while still relying on land and producing methane.
The number that matters depends on the question. Energy per kilogram of product is not energy per 100 grams of protein. Neither tells us directly about climate impact unless we also know where the energy comes from and what emissions are associated with the inputs.
The electricity mix changes the answer
A kilowatt-hour from a low-carbon source and a kilowatt-hour from a high-carbon source provide the same energy service, but they do not carry the same climate footprint. This is particularly important for routes that rely on controlled environments, hydrogen or intensive purification.
That is why a forecast for a future plant should state its assumed energy supply. A result measured in one place and year is not automatically transferable to a different grid or factory.
A practical checklist
When you see a protein-efficiency claim, ask: Is the denominator edible protein? Are feedstock, fertiliser, heat and purification included? Is the electricity source stated? Are co-products allocated consistently? Is this measured at commercial scale or projected from a pilot?
Until the answers are visible, precision is not the same as certainty. Our comparison pages will show where the evidence is strong, where assumptions differ and where a number would be misleading.
The Greensome view
Energy is the quiet test behind many confident claims. Count it across the whole route, use the same protein basis, and say clearly what is measured versus projected. That is the beginning of a fair comparison—not the end of it.