Perfect potatoes for perfect chips

From the field to the fryer - potatoes used for crisps production are sensitive to environmental conditions that affect frying properties, appearance, taste and texture. One of the most unpopular blemishes on chips - dark brown spots - is due to increased carbon dioxide (CO₂) levels during storage. "Consumers want light yellow chips without spots. This consumer demand is the incentive for factories to produce spotless chips," explains Todd Forbush, Vice President of Techmark, Inc, an American manufacturer of ventilation systems for fruit and vegetable storage. Using state-of-the-art techniques, the company's systems monitor environmental conditions to adjust ventilation for the stored product - in this case, potatoes.

Stress affects frying properties

In North America, potatoes for chip production are harvested in July, August and September, whereas chip production runs year-round, either with freshly harvested or stored potatoes. During storage, the potatoes continue to breathe. In doing so, they consume oxygen and internal sugars (converted from stored starches) and produce CO₂, water and heat. Stress increases the respiration intensity of the potatoes and thus their sugar content. The sugars impair the frying properties and lead in particular to dark brown spots. Temperature, humidity and CO₂ concentration - these are the three decisive factors that must be monitored and regulated during storage to ensure quality and reduce stress. If the values of these environmental factors are outside the target range, problems are pre-programmed.

The causes of high CO₂ levels

An increased CO₂ concentration is a stress factor for the storage potatoes. "If CO₂ levels reach 2500 parts per million (ppm), then fresh air exchange should be provided to reduce CO₂ levels," says Forbush. CO₂ can accumulate when building ventilation is turned down to control temperature. Another cause of CO₂ formation is natural respiration activity, which depends on the potato's life stage. The ripeness of the potato determines the respiratory activity. Unripe potatoes have a high respiratory activity, ripe potatoes a lower one. Overripe potatoes, on the other hand, have a high respiratory intensity when they go into hyperactive mode before the end of life," explains Forbush. This so-called senescence is one of the many conditions that Techmark takes into account when designing its ventilation systems.

Quality pays off for farmers

Potato farmers have considerable incentives to deliver potatoes that are as flawless as possible. After all, their payment depends not only on weight, but also on how well their produce meets the chip manufacturers' requirements for frying properties. Techmark works closely with producers to maintain quality standards so that they can secure premiums from processors. If a farmer's potatoes fail to meet the processor's quality standards - typically a defect rate of 15 per cent and below - he may have to find other buyers who will pay less.

Vaisala GMD20 offers reliability

Techmark designs customised ventilation systems that monitor, control and distribute air in potato storage buildings to specification. In buildings where storage potatoes are stacked four and a half to six metres high, adequate ventilation is as important as maintaining air parameters. Techmark relies on the Vaisala CARBOCAP™ GMD20 carbon dioxide duct sensor for its ventilation systems. The Vaisala GMD20 convinces with excellent long-term stability and negligible temperature dependence. The sensor is also suitable for the high humidity that usually prevails in potato storage. In order to lose as little product weight as possible, the humidity is kept as high as possible without the formation of free water. "Vaisala's CO₂ sensors have proven to be extremely reliable," says Forbush. "We can rely on availability within the lead time we need and on Vaisala's customer service."

Economic benefits

Recently, Techmark helped a major North American snack food producer improve the processing quality of chips potatoes delivered by rail. The freight cars were not ventilated and over the course of several days the carbon dioxide concentration rose to levels that affected the frying characteristics. By installing the Vaisala GMD20 duct sensors, Techmark says it was able to improve ventilation control, which had a positive effect on the frying properties of the potatoes delivered by rail. Due to the demands of chip and fry potato processors, who are particularly sensitive to defects, more potato growers are adopting new technologies to monitor and control environmental factors that could negatively impact quality and profits.