How to choose a potato cold store and ventilation system

Processing potatoes are best held at about 7-10°C (45-50°F) with 95-98% relative humidity, and at those temperatures sprout suppression is essential. Cooler storage would suppress sprouting on its own, but it triggers cold sweetening, so processors rely on sprout inhibitors instead.

Storage temperature for processing potatoes

• Chips/crisps and dehydration stock: 7-10°C and 95-98% RH, per FAO, CIP, USDA and university extension sources. Another USDA/AHDB/CPRI compilation gives 8-12°C for chip stock.
• French fry stock: 6-8°C, described as a compromise between sugar control and sprout management.
• Reason for the warmer range: below about 6°C, starch converts to reducing sugars (glucose, fructose). These cause Maillard browning, giving dark, bitter chips or fries and forming acrylamide.
• Sugar targets at processing: under 1.5 mg/g for chips and under 2.5 mg/g for fries.
• Recovery option: potatoes that have been chilled can be reconditioned at 15-20°C for 2-3 weeks to lower sugar levels before processing.

Ventilation and atmosphere

• Maintain 90-95% RH in general storage. Processing stock is held at the higher 95-98% RH.
• Active ventilation prevents condensation and anaerobic soft rot. Temperature fluctuations that cause condensation on tuber surfaces create ideal conditions for disease. USDA Agricultural Marketing Service and Kleinkopf et al. (2003) call temperature management the single most important factor in storage.
• Modern commercial stores also run a 0.5-1.0% CO2 atmosphere (Kleinkopf et al. 2003; Pringle et al. 2009).
• Air-cooled bulk bins with fan ventilation work well where fall and winter air is cool, such as Maine, the UK and northern Europe.
• Controlled atmosphere storage uses low O2 (1-3%) and elevated CO2 (2-5%).
• Before long-term storage, cure tubers at 12-18°C and 85-95% humidity for 10-14 days. This lets wounds heal (suberization) and reduces rot and weight loss.

Stopping sprouting

• Chemical inhibitors: chlorpropham (CIPC), historically the most widely used, 1,4-dimethylnaphthalene (1,4-DMN), ethylene, spearmint/mint oil, and maleic hydrazide (applied in the field, not in store). Sprout suppression is essential for processing stock because of the warm storage temperatures.
• Regulatory note: CIPC has been restricted in the EU since 2020 under European Commission Implementing Regulation 2020/17. Operators there need alternatives such as 1,4-DMN, ethylene or mint oil.
• Temperature: holding at 2-4°C suppresses sprouting, but this is suitable for table and seed stock, not processing stock. Table potatoes are kept at 3-6°C, with inhibitors if storage is extended.
• Seed potatoes: avoid sprout suppressants, because they inhibit sprouting. Store seed at 2-4°C and warm it to 10-15°C 2-4 weeks before planting.

Key takeaway: For processing potatoes, hold them at roughly 7-10°C (6-8°C for fries in some systems) and 95-98% RH with good airflow, and use a chemical or natural sprout inhibitor. Don't chill them to control sprouts, because that raises sugars and darkens the product.