Our recent webinar gives viewers some valuable insights and tips on how to ensure your storage process protects your valuable tubers.
When it comes to storing potatoes, few people know the complexities better than Scott Graham, raw development agronomy manager for J.R. Simplot Company in Winnipeg.
Speaking on our recent Spud Smart Innovation webinar, Graham emphasizes the importance of understanding that potatoes are not just a harvested commodity — they’re living organisms that require careful management throughout the storage process.
“Potatoes are alive, just like us,” Graham explains. “Through respiration, potatoes produce carbon dioxide, water, and heat. Managing this respiration is critical to maintaining a high-quality crop in storage.”
Graham outlines the three pillars of successful potato storage: temperature, humidity, and airflow. These factors, he says, are the main principles for farmers and storage managers to ensure potatoes are stored optimally, preventing dehydration and shrink, while minimizing the risk of rot.
Respiration Management: A Balancing Act
“Temperature is the first and most important factor,” Graham notes. “The higher the temperature, the more respiration occurs that may lead to disease and hotspot issues in storage. Immature or stressed potatoes will respire at a higher rate as well.”
Graham also points out how crop maturity and tuber health significantly affect respiration rates.
“Immature potatoes, that are skinned and have not developed a mature skin set, or those that have been stressed by hail, heat stress, disease or harvested at higher temperatures will have higher respiration.
“This creates more CO₂ and heat in storage, which must be managed through proper ventilation.”
Preparation Starts in the Field
The process of proper storage begins long before harvest. “Tracking stresses during the growing season — like hail, disease, or late planting — is key,” Graham says. “This allows you to determine whether fields should be designated for short-term, medium-term, or long-term storage.”
According to Graham, evaluating crop maturity — both physically and chemically — is crucial. Observing vine health and checking sucrose levels before harvest can help farmers identify potential storage challenges. “For Russet Burbank potatoes, a sucrose level below 1.5 (mg/g) suggests chemical maturity and is ideal at harvest,” he advises.
Harvest Best Practices
Once harvest begins, minimizing damage to the crop becomes the top priority. “Applying pre-harvest irrigation to keep tubers hydrated, avoiding wet spots, and carrying adequate dirt up the chains for cushioning are essential practices,” Graham says.
Bruising is a critical concern. “A good bruise management program at harvest can make all the difference. Record pulp temperature and monitor closely and do not harvest anything above 18 C (65 F), which puts you in the danger zone for increased pathogens and pressure bruise.”
After the potatoes are in storage, the focus shifts to curing and preconditioning. “Curing allows the potatoes to heal wounds and suberize, which reduces water loss and prevents disease entry,” Graham says. He recommends maintaining humidity levels at 95% and temperatures between 11-13 C (52-55 F) during the first two to three weeks to optimize curing.
Preconditioning, Graham explains, is about removing excess sugars before ramping to improve fry colour for processing potatoes.
Managing Long-Term Storage
For long-term storage, Graham highlights the importance of variable frequency drives to maintain proper airflow and minimize temperature differentials within the pile. “Holding temperatures should align with your delivery schedule — warmer for pre-Christmas deliveries, cooler for long-term storage,” he advises.
Reconditioning can be utilized as a vital step if fry colour isn’t optimal before delivery. Increasing your storage temperature to lower sugar results in better fry colour and therefore better french fries.
“Adding supplemental heat and increasing your storage temperature can lower sugar levels, improving fry colour, but it’s critical to monitor CO₂ levels, keeping them below 2,500 ppm to avoid sugar accumulation.”
Care should be taken to slowly increase the temperature to avoid condensation forming on the potatoes.
Routine monitoring is also crucial. “Daily checks for temperature, humidity, and CO₂ are essential. Using sensors to track humidity, temperature and CO₂ can provide real-time data and alert you to potential problems before they escalate,” he says.
Hotter Harvests Demand Cooler Strategies
Rising temperatures during the potato harvest season are forcing Canadian growers to adapt and innovate, according to Mark VanOostrum, supply and quality manager at WD Potato Ltd. He emphasizes the pressing need to rethink traditional approaches in response to changing weather patterns, particularly warmer Septembers.
“September is getting hotter, and it’s not just anecdotal,” says VanOostrum. “I analyzed local weather data spanning 60 years — over 560,000 individual temperature readings — and the trend is clear. Cooling hours during September have drastically decreased from around 300 in the 1960s and 1970s to just over 100 in recent years.”
VanOostrum points out that the trend of increasing hours above 20 C has made harvest conditions increasingly challenging, especially for the chip market, which often requires harvest pulp temperatures in the 12-18 C range.
“In 2024, we recorded over 200 hours above 20 C in September, which is a stark departure from historical norms,” VanOostrum notes. “These hotter conditions delay harvest and impact storage quality, making it critical to adapt our practices.”
The Impact of Temperature on Storage and Quality
Higher storage temperatures elevate the respiration rate of potatoes, leading to increased energy costs and quality concerns. “If you can’t cool the potatoes down fast enough, you’re left with issues like disease, pressure bruises and defects,” VanOostrum explains. “These problems aren’t just about appearance; they affect slicing efficiency, oil absorption, and ultimately, consumer satisfaction.”
A 2016 audit conducted with a storage engineer highlighted significant variability in ventilation capacity across facilities. “Our average storage capacity was 1.1 CFM per hundredweight, but many were below that threshold,” says VanOostrum.
“This year, even our best storage systems struggled. We had only 110 cooling hours in September, but some storages require up to 140 hours to effectively cool potatoes.
“This discrepancy highlights the need for better infrastructure.”
Strategic Adaptations
VanOostrum stresses the importance of variety selection and field management to ensure potatoes are mature with robust skins at harvest. “Not all varieties handle heat equally. Growers might need to adjust their acreage to include varieties better suited to warmer conditions.”
“Storage design and capacity are another critical focus. “Modern storage systems with higher ventilation rates are essential,” he advises. “When potatoes enter storage at 21 C, it can take over two weeks to bring temperatures down to optimal levels if the storage is underperforming.”
VanOostrum believes the industry needs a proactive approach to mitigate the effects of warmer Septembers. “We need to invest in more efficient cooling systems and reevaluate our harvesting calendars based on the length of the growing season for different varieties. It’s also vital to monitor disease risks closely and adapt field practices accordingly.”
Reflecting on the broader implications, he says hotter Septembers are not a passing phase — they’re the new normal. Growers should embrace data-driven strategies and innovative technologies to meet these challenges head-on.
“By doing so, we can ensure that the quality and profitability of our crops remain intact, even in the face of a changing climate.”
Managing Potato Shrink
Understanding and mitigating shrink in potato storage is essential for producers to maintain profitability and reduce losses. John Walsh of J.R. Walsh Consulting provides valuable insights into the causes of shrink and strategies to address them effectively.
“Shrink is the difference between the total weight of potatoes put into storage and the total weight marketed out of storage,” he explains. While the calculation may not always be exact, it highlights weight loss, a critical metric in the storage process.
Shrink primarily occurs due to biological processes and environmental factors. Walsh outlines the key contributors:
- Respiration: “Potatoes are living organisms,” says Walsh. “They breathe, taking in oxygen and releasing CO2, which generates heat and can create storage issues if not managed.” Respiration is influenced by temperature, with the lowest rates observed at 7-10 C. However, harvest damage increases respiration as potatoes work to heal wounds.
- Transpiration: Water loss through the tuber skin and lenticels contributes significantly to shrink. “About 80% of weight loss during storage comes from water evaporation,” Walsh notes. Vapour pressure deficit (VPD) — the difference in water pressure between the tuber and surrounding air — drives this loss. Higher temperatures and lower humidity exacerbate the issue.
- Curing: Proper curing is vital for reducing shrink and improving tuber resilience. Curing at 13-14 C promotes cell repair and reduces respiration-related losses. Mature potatoes require less curing time, while immature ones benefit significantly from this process.
- Sprouting: Sprouts draw water and carbohydrates from tubers, increasing weight loss. Effective sprout control is crucial. “Removing sprouts before sale also leads to direct weight loss,” says Walsh.
- Rot: This is the most devastating cause of shrink. “When rot spreads, losses can be catastrophic,” warns Walsh. Rot often starts with damaged or immature tubers that fail to heal properly. Wet or poorly ventilated storage conditions exacerbate the issue.
Strategies for Minimizing Shrink
Walsh emphasizes several strategies for managing shrink effectively:
- Reduce Harvest Damage: Handle potatoes carefully to minimize bruising and cuts, which accelerate respiration and water loss.
- Optimize Curing: Adjust curing temperatures based on potato maturity to promote healing and reduce shrink.
- Control Humidity and Temperature: Maintain optimal conditions to minimize transpiration and rot risk.
- Monitor and Flag Risks: Walsh suggests a flagging system to identify potential storage risks, such as late blight, wet harvest conditions, or immature crops. “By flagging issues early, producers can proactively manage their storage practices.”
Effective management of shrink requires a deep understanding of the biological and environmental factors at play. “Shrink is inevitable to some extent,” Walsh adds. “But with careful handling, curing, and storage management, we can significantly reduce losses and ensure high-quality potatoes for the market.”