If you have crystals forming at the bottom of your bottles, that means your syrup is too dense. The perfect density is between 66º – 66.9º BRIX.
To prevent crystals in the future, always check density before bottling. If the syrup is too dense, slowly stir in distilled water or sap until the perfect density is reclaimed.
The crystals are NOT harmful to eat, and are NOT indicating that your syrup has spoiled. The problem with crystals is that they compromise the beauty of your syrup and also confuse consumers.
For more details, see our article “When Is Syrup Finished Boiling?”.