Why do some Kosher organisations suggest that dried fruit require a Kosher certification?
One of the reasons offered is that the fruit are often sprayed with compounds to accelerate processing. These are essentially an oil based product and it is suggested that they may be tainted with non-Kosher oils.
High on the list of suspected non-Kosher fruit are the ubiquitous sultanas. They are sprayed with the so called “Grape dipping oil”, a throwback to the early days when the clusters were hand dipped before being dried in the open air. This compound is comprised of oil and a caustic agent, essentially a soap. It has two functions; firstly it breaks down the skin of the grape which permits the moisture in the grape to escape more rapidly, secondly it prevents the light coloured grapes from discolouring thereby producing a “natural golden raisin” (without resorting to artificial bleaching with sulfur dioxide)
These oils, due to the addition of caustic compounds, are not edible, and are therefore not un-Kosher. Only foods can be Kosher or non-K.
Nevertheless, some agencies insist that these oils must be Kosher certified. I have yet to see any Halachic reasoning to justify these demands.