If this concentrate is not processed immediately, another in-line UV unit should be placed in the tubing that brings the concentrate to the storage tank. After processing, syrup quality is affected by filtering and packing techniques, the type of storage container, the storage temperature and the length of storage time. These factors can be responsible for syrup color change and off-flavor development, as well as bacteria or fungal contamination of packed syrup. Care should be taken in using old as well as new filters for syrup filtration. Off-flavors may be imparted to the syrup by the chemicals used to clean and store filters.
Maple syrup is prepared for packing in two ways.
Plastic containers cause syrup to darken after only three months of storage. The syrup packed in tinned steel containers gets lighter in color over time because of increased leached tin and develops a metallic flavor because of high iron content, after the tin coating dissolves. Glass containers also cause darkening of syrup, but not nearly as much as plastic. Occasionally, bulk and retail packed syrup may become color-layered. The top layer becomes gradually darker during storage in non-controlled temperatures.