From FEW: Stressed yeast may be robbing plants of ethanol yield

By Matt Thompson | June 17, 2019

According to Jayne Kalbfleisch, technical development manager at Lallemand Biofuels and Distilled Spirits, one factor that may be robbing an ethanol plant of yield is stressed yeast. “The stress of your biorefinery or ethanol really depends on yeast cells. When yeast gets stressed, bad things happen,” she told a panel during the Fuel Ethanol Workshop and Expo on June 12.

Kalbfleisch said that recognizing stressed fermentation is important, and there are several indicators that may point to stress. “Initially you might see it as an increase in drop glucose,” she said. Other indicators are an Increases in lactic acid, acitic acid climbing late in fermentation, or drop glycerol oscillating across the fermentation process. She also said using a microscope to observe yeast cells and noting the appearance of the cells can help recognize under-performing yeast. An abundance of longer, “sausage-shaped” yeast cells may indicate a stressor is present in fermentation

While yeast cells can often tolerate one stressor, having multiple sources of stress is what can limit yeast activity. “When your yeast cells encounter multiple stressors, their tolerance to any one stressor is going to decrease,” she said.

A key to combating the effects of stressed yeast is to note there is a problem as quickly as possible, and training operators to take appropriate action, Kalbfleisch said. “Always make sure that you know your baseline, and what’s in range and out of range, and make sure your operators know,” she said in regard to monitoring lactic acid levels. “A general rule of thumb is if your lactic doubles, you’re in trouble,” she said.

Kalbfleisch also said that one source of infection may be a plant’s beer column. “Any lactic acid that’s in there is going to recycle back to the front,” she said, highlighting the importance of cleaning the column when an infection is present.

To prevent infections and stressing yeast, Kalbfleisch said ensuring standard operating procedures are followed, plant cleanliness is made a priority, and that responses to any infections or stressors are timely.

“Control what you can to the best of your ability,” she said. “Treat your yeast well, and it will work for you.”