Managing Reducing Sugars in Potatoes Stored for Chip Processing

A bag of chips that fries dark, bitter, and high in acrylocide didn't fail in the fryer — it failed in the storage room months earlier. Reduced sugars (glucose and fructose) react with amino acids under high heat in the Maillard reaction, producing the browning, off-flavors, and acrylamide that processors spend enormous effort avoiding. Dr. Hesham Salah El Askary, in a first-person account of processing-potato storage practice, lays out why controlling these sugars is less about the frying step itself and more about what happens to the tuber for months beforehand.

The account frames the challenge as a biochemical one: sucrose in the tuber is stable, but once it breaks down into glucose and fructose, those reducing sugars are what caramelize and darken during frying. Everything in the storage protocol described exists to keep that breakdown from happening.

El Askary identifies four biological and environmental triggers that push a stored tuber toward sugar accumulation, even in varieties bred for cold-sweetening resistance:

• Cold-induced sweetening: storage below 8°C activates the invertase enzyme, which breaks sucrose down into reducing sugars
• Immature harvest: tubers pulled before full ripeness already carry elevated sucrose and free reducing sugar levels, so they never establish chemical stability once storage begins
• Respiration and CO2 buildup: poor ventilation lets gas levels rise in the store, stressing the tubers and pushing them to convert starch into simple sugars for energy
• Dormancy break and sprouting: once dormancy ends, the tuber physiologically breaks down its starch reserve to feed new shoots, which effectively ends that batch's usefulness for processing

The protocol described holds processing-bound potatoes at 9 to 11°C — a range chosen deliberately, according to the account, because it's low enough to slow respiration and delay sprouting but still high enough to keep the invertase enzyme from becoming active. That's a notably warmer target than table-potato storage often uses, precisely because the enzyme risk outweighs the sprouting risk for this end use.

Alongside temperature, the account specifies continuous ventilation to keep carbon dioxide in the storage atmosphere between 0.2% and 0.25%, expelling saturated air and replacing it with fresh air so the tubers don't experience the stress response that drives starch-to-sugar conversion.

Dormancy management is where regulation has forced a change in practice. CIPC gas, long used to suppress sprouting, has been banned in the European Union, and El Askary's account describes the alternatives now used to keep tubers dormant for export-acceptable storage: mint oil (marketed as Biox-M), ethylene gas, and orange oil (1,4-DMN), each applied at doses recommended in the destination country.

Harvest timing gets equal weight in the account. Fully ripe harvesting after the skins have hardened is described as essential to starting with a low free-sugar baseline, followed by an initial drying period of 10 to 14 days at 15-18°C and 95% relative humidity to heal wounds and scratches from pulling before the potatoes ever go into refrigeration.

The final stage in the account is reconditioning. Potatoes held long-term at 4-5°C to fully suppress dormancy can't go straight to the fryer — El Askary describes raising the temperature gradually, by 0.5 to 1°C per day, up to 15-18°C over two to three weeks before use. That slow warm-up stimulates cellular respiration, prompting the tuber to consume its accumulated reducing sugars and convert what's left back into starch, bringing reducing sugar content down to what the account describes as a safe processing limit of roughly 1% to 1.5% of wet weight.