Chipping quality of potato varieties in the AFBI Crossnacreevy trial programme is being disseminated for the first time through the AFBI website. Results on fry colour and its variation, internal discolouration and, for some varieties, peeling efficiency both after harvest and after a period of storage have been included.
The AFBI Crossnacreevy potato variety evaluation programme routinely assesses potato varieties after harvest and after storage for a number of end-uses – table use, crisping and chipping. Varieties are included in crisping and chipping tests if they have dry matter contents of greater than 20% or if their breeder has claimed chipping and/or crisping as an end-use. Involvement in the DARD Chip Initiative stimulated development in assessment methods which, along with improved data analysis, has enabled AFBI Crossnacreevy to provide more complete information on the chipping potential of varieties.
Potato tubers are metabolically active during storage and this is most readily seen as they begin to sprout. Storage temperature affects fry colour. Colder store temperatures slow down sprouting and prolong storability but produce darker fry colours. Varieties that produce light fry colours when stored at colder temperatures would be highly desirable. AFBI Crossnacreevy has recently introduced assessment of fry colour after storage at colder temperatures as well as the regular storage regime. Preliminary results can be obtained by contacting the potato team at AFBI Crossnacreevy
The chipping tests include the following assessments:
Fry colour
500g freshly cut chips are fried at 190 degrees C for 4.5 minutes.
Fry colour is assessed using the USDA chip colour chart which has seven grades: 000 – 00 – 0 for light coloured chips and 1 – 2 – 3 – 4 for darker coloured chips. The numbers and weights of chips in each of the grades are recorded. This scale is converted into an AFBI 1-7 scale, where 1 = ultra light and 7 = very dark, for ease of computation. The results have been presented as the following characters:
- Fry colour: mean colour of ALL chips
- Colour variation: a calculated measure of the distribution of chips across all colour grades on a 0 – 3+ scale where 0 = no variation, i.e. 100% of the chips found in one colour grade.
Varieties suitable for chipping should have a golden (USDA: 1, AFBI: 4) colour, possibly light (USDA: 0, AFBI: 3) in a few varieties and occasionally dark golden (USDA: 2, AFBI: 5) in some varieties. Ideally the chips should have no variation in colour (0) or be highly uniform (0.01 – 0.25) or uniform (0.26 – 0.50). Fry colour may deteriorate slightly and colour often becomes more variable during storage.
Internal discolouration after frying
Internal discolouration of the chips may occur. This greying of the flesh is similar to that assessed in after-cooking blackening of steamed tubers. It is assessed by slicing 20 chips and determining the discolouration on a 1 – 9 scale where 9 = no discolouration.
Internal discolouration of varieties should not occur (>9.0) but is often very slight (8.5 – 8.9) or slight (7.0 – 8.4). Internal discolouration frequently becomes worse during storage.
Peeling efficiency
This newly introduced test at the request of the DARD Chip Initiative provides information on the weight of chips produced from a given weight of tubers. It is reported as a % and is determined from weights of the tubers before and after peeling.
A high peeling efficiency (>80%) is desirable in chipping varieties with many varieties achieving good peeling efficiency (70 – 79%). Peeling efficiency deteriorates slightly in most varieties during storage.
Variety performance
An initial screening of the varieties has identified those with uniform or highly uniform light or golden fry colour and no more than slight internal discolouration both after harvest and after storage:
Axona, Courage, Daisy, Fontane, Horizon, Lady Claire, Lady Jo, Lady Rosetta, Markies, Mayan Gold, Pomeroy, Ramos, Rembrandt, Sassy, Satellite, Saturna, Verdi, Victoria.
Additional characteristics of the varieties, namely yield and maturity, will determine the realisation of their potential value on farm. Freedom from damage, resistance to blight, shape (long is desirable), may also be taken into account.
DARD Chip Initiative
The DARD Chip Initiative aims to identify and encourage the utilisation of locally-grown potato varieties for chip production in Northern Ireland. Maris Piper is widely used at present and is mostly imported. In AFBI Crossnacreevy tests, locally-grown Maris Piper had a golden fry colour and slight internal discolouration with good peeling efficiency both after harvest and after storage. Its colour was variable, however, whereas all the potential chipping varieties mentioned above had either uniform or highly uniform fry colours. The varieties Cabaret, Fontane, Markies and Rembrandt were identified from the AFBI Crossnacreevy tests as having chipping potential. They are currently being more fully investigated by the Chip Initiative in larger scale field production in conjunction with local chip processors and retailers.
