This article was written by Jorge Luis Alonso G., an information consultant specializing
in the potato crop.
If you’re involved in the potato processing industry, you might be familiar with the issue of “dusting” during the final frying of par-fried and frozen French fries. Recognized as a major quality concern, the industry is actively seeking solutions by adjusting processing parameters.
A recent research program, inspired by a similar issue in par-baked French baguettes, was developed to investigate this problem. R.G.M. van der Sman and Bjorn van den Oudenhoven examined dust formation by altering the standard processing of French fries and assessing the physical properties of the samples.
Van der Sman is affiliated with Wageningen Food & Biobased Research in the Netherlands, while Van den Oudenhoven works at Lamb-Weston Meijer in Kruiningen, the Netherlands. The researchers published their findings in the journal Current Research in Food Science, with their paper titled “Dust formation in French fries” available here.
So what causes this annoying dusting, you ask? Well, according to Van der Sman and Van den Oudhoven, much like the flaking problem with par-baked French bread, it all boils down to damage to the crust during the pre-processing stage. This damage causes the crust to fracture during final frying, resulting in the release of small fragments — otherwise known as dust. This damage is caused by the freezing step, and it is related to the different physical properties of the core and crust regions of the French fries during freezing.
Van der Sman and Van den Oudhoven found during their research that the build-up of high tensile stresses due to these differences in material properties can result in microcracks that can grow during the thermal shock of the final frying. The amount of dust can be controlled by increasing the moisture content of the crust. Similar problems occur with other baked goods due to thermal stress during rapid temperature changes.
According to Van der Sman and Van den Oudhoven, factors such as the amount of moisture in the crust after frying, freezing rate, and frozen storage time all play a role in dust formation. However, frozen storage time appears to have the greatest effect on dust. Pre-treatments don’t seem to have much of an effect. Dryer and fryer treatments reduce moisture in the crust region, and changes in dry matter content affect the freezing rate.
During freezing, ice expansion occurs only in the core region, causing stretching of the dry crust region. Dust formation occurs due to the fracturing of the crust during final roasting, resulting in stress accumulation in the crust. Microcracking occurs during parfrying or freezing, and Young’s modulus increases with decreasing moisture content. The critical viscosity for the development of thermal stresses during freezing is η = 107 Pa s, and long relaxation times develop at large viscosities that scale with Tg/T.
After studying dust formation during the final frying of frozen French fries, Van der Sman and Van den Oudhoven found that all steps in the production chain contribute to dust formation. However, crust moisture content, freezing rate and frozen storage time are the most important physical factors. Frozen storage time reduces dust due to moisture migration.
To combat this problem, a non-linear regression model was proposed for the initial value of dust. While these results provide the industry with tools to reduce the dust problem, it’s important to note that any action taken may impact other objectives.
Source: R.G.M. van der Sman, Bjorn van den Oudenhoven, Dust formation in French fries, Current Research in Food Science, Volume 6, 2023.
Author: Jorge Luis Alonso G. is an information consultant specializing in the potato crop. He writes marketing materials for Ag-Tech companies.
Image: Credit Ande Hazel from Pixabay