Sprouting and losses in store

Processing potatoes need warmer storage than table stock, which means sprout control has to come from suppressants, because cold alone can't do it without ruining fry colour.

Temperature and humidity for processing potatoes

• Chips/crisps, flakes and dehydration: 7-10°C (45-50°F) at 95-98% RH, according to the harvest and post-harvest literature (FAO, CIP, USDA, university extension, ICAR-CPRI).
• USDA and CPRI-based storage guidance gives somewhat different figures: 8-12°C for chip/crisp stock and 6-8°C for French fries, a compromise between sugar build-up and sprout management.
• Below about 6°C, starch converts to reducing sugars (cold sweetening). This causes dark, bitter chips and fries and raises acrylamide through the Maillard reaction.
• Target reducing sugars at processing are below 1.5 mg/g for chips and below 2.5 mg/g for fries.
• Cold-stored lots can be reconditioned at 15-20°C for 2-3 weeks to lower sugars before processing.

Ventilation and atmosphere

• Commercial stores run at 90-95% RH with 0.5-1.0% CO2 (Kleinkopf et al. 2003; Pringle et al. 2009).
• Active ventilation prevents condensation and anaerobic soft rot. Humidity below 85% causes shriveling and weight loss.
• Fan-ventilated bulk bins using cool ambient air work well in cool climates such as Maine, the UK and northern Europe.
• Controlled atmosphere (CA) storage uses 1-3% O2 and 2-5% CO2.

Stopping sprouting

• Because processing stock is held at 7-10°C, sprout suppression is essential.
• Options include chlorpropham (CIPC), 1,4-dimethylnaphthalene (1,4-DMN), ethylene, spearmint/mint oil and maleic hydrazide (the last is typically applied in the field).
• CIPC has been the most widely used, but it has been restricted in the EU since 2020 (Implementing Regulation 2020/17). Approvals differ by country, so check local rules before using it.
• For table stock, cooler storage at 3-5°C suppresses sprouting on its own, though a suppressant may be needed for long storage.
• Do not use suppressants on seed potatoes, since they inhibit sprouting. Seed is held at 2-4°C instead.

Curing first: hold tubers at 12-18°C and 85-95% humidity for 10-14 days after harvest so wounds heal. This reduces rot and weight loss in storage.

Key takeaway: store processing potatoes at roughly 7-10°C (6-8°C for fries in some guidance) with high humidity and good airflow, and rely on suppressants rather than cold to control sprouts.