Dried figs and raisins are microbiologically stable; returned lots typically involve swings in temperature and humidity. The Transport Informations Service (TIS-GDV) puts the favourable travel range at 4 to 20 °C: below 10 °C mite growth is inhibited, and above 25 °C syrup formation, candying and fermentation begin.
Relative humidity should be 60-70% for figs and about 65% for raisins. Below 60% the product hardens, and raisins above 70% turn tacky, grow mould and ferment. The white coating on the surface is crystallised sugar, not mould, and it increases as temperature and humidity swing.
Sweat from container surfaces wets the product and starts fermentation, so the lot is protected with dunnage. The first measure that keeps infestation to a minimum is good store hygiene; treatment comes on top of it.