Evaluating processing performance: Insights from the Marble Hall processing cultivar trial
Estimated reading time: 3 minutes
The Marble Hall processing cultivar trial took place on 5 June this year. The trial has been running for a few years and has provided valuable information on up-and-coming processing cultivars. This year, we evaluated a total of 11 cultivars.
Potato cultivar trials play an important role in identifying varieties best suited to the processing industry.
While yield remains an important consideration for producers, a cultivar that performs well in the field must also meet processors’ quality requirements.
Processing trials therefore evaluate a range of characteristics, from tuber quality and specific gravity (SG) to chip colour, dry matter (DM), and cooking performance.
Potato quality characteristics
One of the key measurements in a processing cultivar trial is SG, which indicates the DM content of the potato and is closely associated with processing yield and product quality.
Generally, potatoes with a higher SG and DM content are desirable for products such as French fries and crisps, as they tend to absorb less oil and produce a better texture. However, the ideal SG can vary depending on the specific product being processed and the processor’s requirements.
Chip colour is another critical quality characteristic. Potatoes are processed into chips or fries, and assessed for colour after frying. A light, uniform golden colour is generally preferred, while excessively dark chips can indicate high levels of reducing sugars.
These sugars, particularly glucose and fructose, can increase during storage and may result in darker frying colours.
Cultivars are therefore assessed not only directly after harvest but also, where applicable, following storage to determine how well their processing quality is maintained over time.
The DM content of tubers is also assessed, as it influences texture, processing yield, and oil uptake. Higher DM can contribute to a desirable crispy exterior and mealy interior in French fries. Alongside this, the trial considers the distribution of tuber size and shape. Uniform, appropriately sized, and well-shaped tubers are easier to process and improves peeling, cutting, and processing efficiency.
Cultivars’ physical quality
Physical quality is equally important.
Cultivars are evaluated for mechanical damage, bruising, greening, common scab, growth cracks, hollow heart, internal defects, and other blemishes.
These characteristics affect the usable yield of a crop and the final quality of the processed product. The number and severity of defects are recorded to determine whether a cultivar can consistently meet the quality requirements of the processing sector.
Fry quality and texture are also considered during processing evaluations. Depending on the end product, factors such as crispness, internal texture, oil uptake, and uniformity can provide valuable information about a cultivar’s suitability.
For French fry production, fry length, shape, and colour uniformity are particularly important because they influence both processing efficiency and consumer acceptance.
Storage performance should also be considered when selecting processing cultivars. A variety may perform well immediately after harvest, but change during storage as sugars accumulate or tuber quality deteriorates. Monitoring weight loss, sprouting, sugar levels, and fry colour after storage provides a more complete picture of a cultivar’s processing potential.
Ultimately, a successful processing cultivar must offer a combination of agronomic performance, yield, tuber quality, and consistent processing characteristics. By evaluating SG, DM, chip colour, tuber size and shape, defects, fry quality, and storage performance, cultivar trials provide valuable information to producers and processors when deciding which varieties have the greatest potential for the processing market. – Damien Da Cal, Potatoes SA
Special thanks to all the seed houses that participated in the trial, as well as the producer for providing the labour and his expertise. Additional information about this trial will feature in an upcoming issue of CHIPS. Send an email to damien@potatoes.co.za for more information.