Temperature is the Enemy
Excess temperature can also put stress on the yeast, therefore, temperature must be monitored closely. Fermentation is an exothermic reaction, so heat is a byproduct of the process and causes the fermenter temperature to rise. As the temperature rises, stress on the yeast causes the fermentation rate to decrease, which results in decreased alcohol production and yield.
To remove excess heat, cooling coils inside the fermenter are used to manage fermenter temperature. Unfortunately, this can lead to another issue in larger distilleries where multiple fermenters share the same cooling water header. With this set up, changing the water flow to one fermenter will likely change the flows to the nearby fermenters, and operators simply do not have time to continuously and manually adjust all the flows to achieve consistent temperatures.
Regulatory control loops can be used to address this issue, but, given the interactions, aggressively tuned loops will oscillate, potentially inducing temperature variation, and sluggishly tuned loops will provide sluggish control.
Instead, MPC can play a significant role in maintaining consistent temperatures during fermentation. Since MPC is multivariate in nature, it allows the management of all the fermenter temperatures to be solved at the same time. The “model” part of MPC accounts for the interactions between the flows, while also accounting for disturbances, such as changes in the temperature of the cooling water.
Boost Yield and Production with MPC
By managing the stressor variables, MPC positively contributes to the process of fermentation by improving yield and batch consistency. As variability is reduced, an optimization opportunity is presented.
There is a strong correlation between alcohol yield and the fermentation time, however, as the fermentation time is extended, the rate of ethanol production drops off. As a company, you must decide what is preferable depending on your production needs, bottlenecks elsewhere in the plant, commodity prices and other external factors: increased alcohol yield in the same fermentation time, or the same alcohol yield in a shorter fermentation time, allowing more batches each month, or something in between?
As distilled spirits producers work to increase production while maintaining recipes and product integrity, MPC can create opportunities and encourage these outcomes at each step of the way.
If you want to learn more about the benefits of MPC in the spirits industry, read more here.