We test the newest varieties as to their agronomic and processing qualities for the manufacture of crisps and chips. Variety-specific resistance to potato late blight, viral diseases and the powdery scab pathogen are of special importance for farmers. Together with the branch we publish annually a list of the recommended potato varieties.
As part of the certification of the plant material, we collect information on the regional and seasonal occurrence of various aphid species that play a major role in transmitting viral diseases. This information is made available on an ongoing basis to seed-propagation organisations by means of bulletins. In addition, we are responsible for the training of the field-inspection experts and seed-stock inspectors.
Disease-resistant, high-quality varieties and healthy seed-stock that is as free of viruses as possible form the basis for environmentally friendly and cost-efficient potato cultivation.
Knowledge of cultivation techniques and of suitability for storage and processing allow for optimal production and utilisation.
Agroscope focuses on regional issues and develops recommendations for both integrated and organic potato production.
Suitability for Manufacturing Processed Potato Products
Today, more than 50% of the potato produced for human consumption is used to manufacture various processed products such as crisps, chips, Rösti (hash browns) and other dishes. Raw materials of consistently high quality ensure the quality of the finished product. The most important traits for potatoes destined for processing are a good shape of the tuber for the product in question, low sensitivity to shock, no internal defaults such as hollow cores and rust spots, low reducing-sugar content, and good suitability for storage of the tubers. Very low reducing-sugar content is the prerequisite for a light colour after frying.
Standardised frying tests
Tuber material from a number of variety tests is processed on several frying dates from November to May. Since both the origin of the tubers and the storage conditions for all varieties at a given trial site are identical (storage temperature of 8°C, one-off chlorpropham (CIPC) treatment to inhibit sprouting), the reducing-sugar content can be indirectly estimated on the basis of the colour of the fried crisps.
Suitability for crisps
Ten to twelve tubers per variety are peeled and sliced into 1.2mm-thick discs. The sliced potatoes are rinsed twice in lukewarm water to rid them of excess starch. Any water clinging to the potatoes is shaken off before deep-frying. The crisps are then fried for 3 minutes at 170°C in a small deep-fryer in high-oleic sunflower oil, stirring constantly. The colour of the fried crisps is assessed visually, according to the Wageningen Colour Reference Card (IBVL colour card for evaluating crispness).
Suitability for chips
Selection criteria are tubers with a long oval shape, a starch content ranging from 14–17%, and a minimum frying colour of level 5 for the chips. A potato chipper is used to cut the peeled tubers into 8mm x 8mm fries. They are then blanched at 150 °C for 4 minutes, and visually checked one hour later for unwanted grey discoloration (darkening) from the frying. Afterwards, they are either refrigerated for a day at 4 °C, or deep-frozen at -25 °C for several weeks. Finally, they are fried off at 170 °C for 3 minutes. The sample is then checked visually for frying colour, inner and outer condition, and texture. Taste criteria evaluated are the crispness (toughness, stodginess) and oiliness of the fries.
Suitability for Rösti (hash browns)
Suitable varieties from two origins in each case are selected from the main trials. For one sample, 800g of unpeeled potato is boiled for 40 minutes. The next day, 500g of these boiled potatoes (peeled weight) is grated and salted. Forty grams of peanut or sunflower oil is then heated in the frying pan, and the grated potatoes are fried on both sides for 10 minutes. The Röstis are tasted and rated by six individuals. For a positive rating, the following criteria must be met: The crust must be golden-brown and taste slightly nutty; the shreds must not be burnt and bitter-tasting; the shredded mass must not be too stodgy and heavy, but neither should it be too loose and dry; and the shreds should not break down into a mush when fried.
