One of the more challenging products to IQF freeze is the raspberry. This has everything to do with its brittle and delicate texture. With the correct equipment however, the product can be handled for good profitability. To achieve the best quality it is recommended to pick ripe berries on a day willed with sunshine. Not every day fits this criteria and the ripening of raspberries follows its own time table. The technology of Individual Quick Freezing (IQF) keeps the healthy properties of the fruit at the same level of the fresh counterparts.
Challenges of processing raspberries
IQF freezing raspberries is the easiest process, says Ruben Larsson, founder of OctoFrost. “By nature, cold raspberries (-18 to -22 C) are brittle and sensitive to breakage when they reach the end of the freezing process. This is why it is crucial to reduce the airspeed and agitation of the soft fruits as they reach colder temperatures. To ensure any unnecessary breakage is prevented, a zero drop design at the outfeed of the processing line is required. Thanks to OctoFrost’s freezer with zero drops, controlled fluidization and reduced airspeed alongside the freezer, it’s possible to achieve 98-99 percent A-quality berries.”
Overripe berries
Overall, raspberries can be categorized by their ripeness, and according to Larsson one can net different result depending on the grade of over-ripeness of the berries: “Harvesting the berries on a rainy day, or picking them when they are overripe can cause a reduction in performance to about 90 per cent for A-class berries. If the freezer is not well designed, that number can drop to 80 percent, with twenty per cent being crumbled or broken. The quality of the machine can therefore have a direct impact on the profitability of IQF frozen berries.”
Another option is trying to IQF freeze heavily overripe berries, which can increase the losses to about 50 percent, Larsson says. “This situation can occur near the end of a season. For these berries, a solid freezer can achieve 50 percent A-Class berries. With a type Belt Freezer, all the berries must be frozen as pulp.”
Getting the pre-work done
“When categorizing the raspberries by its ripeness, it does not take away the requirement to pre-cool berries before entering the freezer for better results. This is done in cooling chambers with an air temperature that is just below the freezing point. Some markets require you to apply a light spray of chlorine.”
The OctoFrost processing line
“In our IQF processing line, it’s possible to set the speed of the fans independently from each other. You could also control a group of fans in a single freezing zone for convenience,” Larsson explains. “To maintain separation, the fan speed near the entrance of the freezer is set rather high. After that, the fan speed slows down until the produce is frozen, to avoid damages on the raspberries. Naturally our freezer is designed to reduce damages at the end, with a close to zero drop at the outfeed of the freezer. Thanks to our design it’s also possible to get the temperature below -20C to avoid lump formation in boxes when they reach cold storage.”
Reducing dehydration
Finally, Larsson says the OctoFrost line has been designed to reduce dehydration by one to three percent. “This is a significant economic advantage for a relatively expensive product; lesser dehydration means about the same per cent of higher yearly invoicing, without having to spend more money on raw materials, electricity or manpower.”
