Running hot: 7 tips for warm weather ethanol fermentation

By Claudia Geddes, Senior Scientist, Technical Service, Novozymes

Special to The Digest

It’s been a scorcher of a summer for much of the U.S., including the more than 25 states with ethanol production facilities. But while the dog days of summer may be behind us, record-setting temperatures are still in the forecast for many producers.

As you know, heat—and its partner in crime, humidity—can be a stressor on the yeast used in ethanol fermentation, affecting both yeast health and performance. Unfortunately, this often makes yeast a bottleneck for plants, as not all plants have the cooling capacity to account for peak summer production rates at the highest possible sugar levels.

Of course, not all yeasts are created equal, and some are better suited to withstand adverse process conditions. Nonetheless, there are still steps that can be taken to maintain (or improve) the health of even the most robust yeast, despite these higher temperatures.

Effectively dealing with temperature stress

The easiest way to reduce fermentation temperature is to reduce the sugar level going into fermentation. This, however, is a tradeoff that reduces yeast growth and activity. Temperature staging, where the temperature is gradually reduced to lower levels than typical later in fermentation, can also help lighten stress and avoid premature yeast death.

Here are seven more common strategies to beat the heat and achieve good fermentations:

1. Chiller inspection

• Supplement cooling requirements with chillers, refrigeration systems that focus cooling within the process.
• Have your chillers inspected and in good working order.

2. Prepare for increased copper levels

• Chillers can increase the copper content of cooling water blowdown, the water drained from cooling towers to remove mineral build-up.
• Know your permitted copper levels prior to starting chillers and discuss them with your water treatment vendors. This can help avoid mishaps that could arise from elevated copper levels.

3. Allocate chilled water resources

• Since fermentation demands much of the available chilled water, reserve some for distillation exchangers, and to confirm that you’re effectively balancing cooling water between fermentation and downstream processes.
• Map out a heat exchange strategy with cooling tower control valves and open percentages. Prioritize chilled water to fermentations during the highest metabolic state, typically occurring 12 to 24 hours into fermentation.

4. Standardize chiller water allocation procedure

• Standard procedures for all parts of the plant reduce process variability and avoid hot fermentations.
• Hot fermentations impact yeast growth. They can cause conditions favorable to bacterial infection, lead to lower ethanol yield, increase organic acid concentrations and higher remaining sugars.

5. Avoid repeatedly turning chiller on and off

• Minimize the number of times the chiller is turned on and off. The greatest cost associated with running a chiller is the high peak electrical demand needed to turn it on.

6. Decrease corn solids loading

• Reduce corn solids to help control yeast metabolism and fermentation temperatures. Checking the temperature forecast every 24 hours, along with planning solids loading accordingly, can help avoid yeast temperature stress.
• The higher the temperature, the lower the solids loading should be. It’s also recommended to maintain the temperature of the mash entering the fermenter at 88°F (31°C). Starting at a lower temperature will help prevent the fermentation from getting to 96°F (35.5°C), thereby reducing the potential stress on the yeast.

7. Monitor supplemental nitrogen

• Give the yeast what they need when they need it. During warmer months, this means paying closer attention to how nitrogen is being dosed.
• Nitrogen will accelerate yeast metabolism—however, if too much nitrogen is dosed early on in fermentation, excess heat will be produced.
• Consider using a protease to supply amino nitrogen that the yeast can utilize, which can help combat heat stress while reducing the need for supplemental nitrogen.

These are just a few of the process adjustments you may have to make to ensure optimized fermentation in warmer weather. But even if 2017’s triple-digit temperatures are behind us, it’s never too early to proactively make a few process adjustments. After all, spring will be here before you know it.