Blueberries are useful in a wide range of finished foodstuffs, and are available to the consumer as fresh, frozen, and dried products.  Historically, Blueberries that were dried came from fresh fruit processing, and resulted when the fresh fruit was culled for immature, overripe and off-grade defects.  We were drying culls!  Today, the demand for dried fruit and the over-production of Blueberries has resulted in the drying of high quality fresh fruit during harvest, and later in the year, as frozen Blueberries that are thawed and then dried, all depending on consumer demand for fresh and frozen products. 

Due to the wide variety of uses, and varying specifications for each application, the dried Blueberry exits the dryer at a variety of moisture contents.  When used to flavor Ice Cream, and jellies /jams, the target Moisture Content (TMC) can be as much as 50%.  Applications like trail mix require the fruit to be in the 15% to 20% range.  When used in pancake/muffin mixes where the dried fruit and flour mix are not separated, the TMC must be at 5% to 7% to prevent clumping.   To maximize product quality, and minimize loss through dehydration, many processors sugar infuse Blueberries prior to dehydration. 

NOTE: In most cases Blueberries are harvested for fresh consumption, allowing for final ripening during freight, distribution, and on the grocery shelf.  This affects frozen Blueberries and really affects the fruit that is dehydrated (fully ripe fruit are best suited for dehydration). 

For small and medium volume processors, tray drying Blueberries is the most cost effective procedure.  We generally recommend a process air temperature of 165 degrees (F), air velocities of at least 500 feet per minute, and Relative Humidity (RH) of 17% to 19%.  The most popular methods for tray drying Blueberries include Counter-Flow, and Batch to Dry.  Parallel-Flow is problematic with case hardening as the primary issue, and Classic Batch results in uneven product moisture content from car to car. 

Pre-dehydration sizing improves fruit consistency and overall quality.

Please remember your Dryer is not a “magic machine”; and just like computers: garbage in = garbage out.  High quality dried fruit must start out as high quality fresh fruit, harvested at the peak of ripeness.   Yes, we can augment the sugar content, and extend the availability of the fruit by freezing, but ultimately quality begets quality, and quality sells!

One last note: If you dry previously frozen fruit, and then attempt fresh fruit, you will notice that the fresh fruit takes longer in the dryer.  The shortened dwell time for the previously frozen product, is due to the slow freezing of the fruit.  When cells in the fruit freeze, the cell membranes burst, allowing “free water” to escape at a much faster rate than fresh.

The very last note:  Blueberries are dried whole, with the skin intact, however, some progressive operators are now passing the fresh fruit through a set of rollers, set just tight enough to split the skin (not crush the fruit), and thus are achieving significantly reduced dwell times.  The fruit must be sized prior to this operation.