The refinery is a building which will help you get rid of the minerals that you have left over, it has several cubes which change with the level of the structure, keep in mind that the higher the level of the refinery, the better reward they can give you the cubes. The refinery costs 62,000 gold and can be built from starbase 3.
Once built you can start refining cubes with minerals, these are divided into 3 cubes:
- Flawed Present -> Level 1
- Imperfect Present -> Level 2
- Perfect Present -> Level 3
Each level has a better reward than the previous one, but it takes longer to refine than the previous one, being the best possible reward obtained in Level 3 (Perfect Present).
Rewards range from:
- Collection Items
- Help in battle
- Resources (Does not return minerals)
* (Not confirmed, just speculation)
The more level the refinery has, the better and bigger these rewards will be. Good luck!