July/August 2021
Cost of keeping potatoes cool in storage going up due to rising temps By Melanie Epp, contributing writer

Five years ago, Ruth and Nick Ploeg invested in a new chiller, as they found they were storing potatoes well later and later each year. The chiller provides more cooling capacity, which has been especially handy in unseasonable weather. 

Industry experts believe this type of investment will be more common in the future. As weather patterns become more variable and unpredictable, quality could be impacted in long-term storage. Industry professionals offer expertise on how to mitigate losses due to that increased variability.

The Ploegs grow 1,450 acres of potatoes in Alliston, Ontario, where temperatures soar in summer but drop well below freezing in the winter. Ruth said the chiller has already paid off. 

Last November, the province was hit with unseasonably high temperatures, rising to 77℉ (25℃) during the day and dropping no lower than 60℉ (16℃) at night.

“You can’t cool potatoes at those temperatures,” she said. “So we turned on the chiller.”

This April, at a time when snow is normally just beginning to melt, the province was hit with high-70s temperatures again, forcing the Ploegs to fire the chiller up a month and a half earlier than they normally would. With each bin worth an estimated CAD $300,000 (about $240,000 U.S. dollars), they’re grateful to have a quick solution to preserve quality when needed. 

“We can’t take a $300,000 hit,” said Ruth. “Maybe once in a while, but not consistently, we can’t do that. We wouldn’t be in business.”

The Ploegs installed the chiller on the advice of Todd Forbush, an engineer at Techmark, who said it was a better option than air conditioning, which often causes shrinkage.

Forbush said the Ploegs situation isn’t unique. Most potato growers don’t have a dependable supply of ambient air for cooling where temperature variability occurs. Without cooling, though, potato stores could start building up heat and moisture, allowing pathogens to reproduce and destroy the tubers.

“To mitigate the risk, we’re really looking at additional mechanical cooling and better ventilation practices,” said Forbush. “So excessive fan run time when the outside conditions are not favorable is something we need to focus on, especially in ambient cold storage.”

Techmark participated in a study out of Michigan State University, led by environmental science and geography professor Julie Winkler. The study evaluated historical weather data in the state, and using climatological models, predicted temperatures will be warmer than the desired storage temperature in the long term. 

When asked what growers could be expected to invest to improve cooling in their storage units, he said it was too difficult to predict. With steel and lumber costs being as high as they are currently, it may not be the ideal time to build. And while some stores could be retrofitted with a refrigeration unit or chiller, many will need to be rebuilt entirely. Return on investment will heavily depend on regional weather patterns and the overall risk changes in those patterns bring. 

Some growers are concerned about the increased cost that comes with running refrigeration units longer and more often. They’re also concerned about what refrigeration does to potatoes in long-term storage. Refrigerating potatoes means losing moisture out of the potato, said Erwin Zandstra, sales engineer at Tolsma-Grisnich

“Of course, you can add humidity, but also, if you can control your storage the way we do it — based on product temperature and the needs of the product – you can minimize your refrigeration and ventilation hours,” he said. 

Harvest conditions impact long-term storage

Changing weather patterns don’t just impact pulp temperature at harvest; they also significantly narrow harvest windows, said University of Idaho potato specialist Nora Olsen. With a lot of acreage to get out of the fields in a short amount of time, it’s possible that growers are harvesting outside the recommended range and into riskier harvest temperatures.

Once harvested, growers will need to remove field heat in storage and cool potatoes as quickly as possible. Where outside temperatures remain warm, growers will need to rely on refrigeration to do this, she said. 

But not all U.S. potato storages are equipped with refrigeration. In fact, Forbush said most are ambient stores. If used, refrigeration needs to have the high capacity to remove that kind of heat, said Olsen. Where cooling air is not abundant, a ventilation system can be used to bring in cool air, and that means increased airflow. 

Nora Olsen examines sprouting potatoes at the University of Idaho research center in Kimberly. Photo: Bill Schaefer Photography

“In our arid regions, we can use evaporative cooling to our advantage to further cool the incoming air into the storage and provide more cooling,” said Olsen. “This will provide greater opportunity to either get to our target temperatures, as well as maintain, even under warmer conditions.”

Coming out of the field, high pulp temperatures need to be removed in order to lower the risk of disease development, weight loss and the potential for pressure bruise, further aging of the crop, and overall reduced quality. Olsen said variety development to withstand these warmer conditions will be needed. 

Shorter dormancy is another risk of storing uncooled potatoes. Tubers that are agronomically stressed from high temperatures, insect pressure or poor skin set, can become physiologically aged, said Brian Winn, Global Sales Director of 1,4Group.

1,4Group offers a dormancy enhancer that helps deal with the stresses of a tough agronomic season. 

“When a tuber becomes physiologically aged, it’s going to want to sprout earlier than it normally would compared to a tuber that had a nice even growing season,” said Winn.

“But storage isn’t a hospital,” said Winn. “Nothing is going to get better in storage. Our job is to maintain as much quality as we can when we transition from the field to the storage.”

In the end, in order to preserve tuber quality under increasingly variable conditions, growers will need to employ a mix of all available tools, including dormancy enhancers, refrigeration and management practices.

Top photo: Alsum Farms & Produce

75 Applewood Dr. Ste. A
P.O. Box 128
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