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Increase Optimization Without Changing the Recipe

Last month we discussed some of the latest trends and opportunities when distilling spirits. In summary, to meet rising demand, companies need to improve and minimize this time-intensive process any way they can, and model predictive control (MPC) technology supports distillers as they optimize their facilities and operations.

While MPC technology helps eliminate inconsistencies during distillation, it can also help improve yield and quality during fermentation.

What is Fermentation?

Leading up to the fermentation process, grains such as corn, barley, rye and wheat are milled to a fine powder. The powdered grains, along with water, are put into mash cookers and cooked at temperatures near 200 degrees Fahrenheit.

Towards the end of the cooking stage, the temperature is reduced, and malted barley is added. Next, enzymes from the malted barley break down the grain starches into simple sugars that can be fermented into alcohol. The mash, along with yeast and water, is then cooled and transferred to a fermenter.

Fermentation typically lasts around 72 hours but varies depending on spirit type and local conditions. As the mash rests in the fermenter, the yeast converts the simple sugars into ethanol, transforming the mash into distiller’s beer.

Reducing Stress Levels

Yeast does not perform well under stressful conditions. During the fermentation process, there are several yeast stressors that affect alcohol yield and other qualities of the resulting distiller’s beer, including pH levels at the start of fermentation and the temperature over course of fermentation.

Managing these variables with MPC technology can help to relieve stress on the yeast, resulting in consistent alcohol yields and a final product that lives up to brand guidelines and expectations. Relying on MPC to handle these variables also frees up operators so they can focus their years of experience and time on higher value tasks.

Managing Fermenter pH

The pH at the start of fermentation has a significant impact on the resulting distiller’s beer because acidity is a stressor on yeast. If the set pH is too low, the yeast will not be as productive and alcohol yields will be reduced. If the set pH is too high, unwanted bacterial growth may occur, resulting in reduced yields, off flavors in the spirits or, potentially, loss of the batch.

For spirits such as bourbon and Tennessee whiskeys, some previously distilled mash, or sour mash, is added to the fermenter. The amount and the acidity of the sour mash will affect the set pH of the fermenter.

Because the sour mash is a recycle stream, variability in one batch may echo and cause variability in another batch several days later. While this effect may settle out over time, MPC offers the opportunity to gradually adjust the ratio of sour mash and water sent to the fermenter. In this instance, MPC consistently manages the fermenter and set pH, ensuring consistent alcohol yields and adherence to traditional recipe targets.

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.

Kent Stephenson
Kent Stephenson
Principal Engineer, Rockwell Automation
Kent Stephenson

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