Fry potatoes need high dry matter and low reducing sugars. High dry matter gives a crisp outside and a floury inside, while low sugar keeps the fry light in colour and helps limit acrylamide.
As a rough illustration, processors often look for dry matter somewhere around the low 20s percent and reducing sugars well under a few tenths of a percent of fresh weight. These are not universal standards. Each plant sets its own intake limits for its process and customers.
Why dry matter matters
Dry matter is the part of the tuber that is not water, mostly starch. Low dry matter potatoes give limp, oily fries because more water must be driven off during frying. Very high dry matter can make fries brittle and prone to breaking.
Plants usually measure dry matter by drying a sample, or estimate it from specific gravity by weighing tubers in air and water. Results are checked lot by lot at intake.
Why sugar matters
Reducing sugars, mainly glucose and fructose, react with amino acids during frying. This is the Maillard reaction. It browns the fry and also forms acrylamide. High-sugar potatoes give dark fries, dark ends and a bitter taste.
The EU has rules requiring food businesses to apply acrylamide mitigation measures and to monitor against benchmark levels, and fries are one of the named product types. Other markets have their own guidance. Check the current requirements with your national food authority.
What raises sugar, and how plants control it
Processing potatoes are usually stored warmer than table potatoes, with sprout control and careful ventilation. Plants test intake lots with fry tests, cutting and frying sample strips to check colour. Blanching also leaches some sugar out of the strips before frying.
Late in the storage season, colour can drift. That is one reason quality sometimes drops after the first container.
The main causes of high sugar are listed below.
- Cold storage: potatoes stored too cold convert starch to sugar, known as cold-induced sweetening.
- Immaturity: tubers lifted too early often carry more sugar.
- Stress: heat or drought during growth can raise sugar.
- Long storage and sprouting: sugar can rise again late in the storage season.
- Variety: some varieties are naturally more resistant to sweetening.
What to ask for
You do not normally buy raw potatoes, so focus your spec on the finished fry. Still, ask the plant for its intake data, as it predicts what you will receive.
- Intake limits for dry matter or specific gravity.
- Intake limits for reducing sugars, or a fry colour test result.
- Storage temperature records for the lot.
- Acrylamide mitigation steps and any test results.
- Finished fry colour on an agreed chart after your frying method.
How we help
During audits we check how each plant tests potatoes at intake and in storage, and we review the records for your lots. We can arrange acrylamide and other tests at an NABL-accredited lab. Ask for a free sourcing review.