With the aid of a mathematical model describing the interrelationships between mycelial morphology, mycelial growth and product formation, rheology, mass transfer, and environmental conditions, a new scale-up strategy has been developed, simulating the bioreactor performance at different agitation speeds. The simulations have shown that there is an optimum agitation speed, yielding maximum product formation that is different from the conventional scale-up results based on constant P-g/V-T, k(L)a and NIDI. It has also been shown in the simulations that the product formation scaled up by means of conventional methods is considerably lower than the simulated maximum or is close to the maximum but requiring a higher energy consumption. This indicates that model-based scale-up could be a more accurate and efficient method for scaling up complex systems such as mycelial fermentation processes.