How do you determine acid insoluble ash in biscuit?

To determine acid insoluble ash in biscuits, first, the biscuit sample is incinerated to remove organic matter, leaving behind inorganic ash. This ash is then treated with a dilute hydrochloric acid solution, which dissolves the soluble minerals. The remaining residue, which is the acid insoluble ash, is collected, dried, and weighed. The weight of the acid insoluble ash is then expressed as a percentage of the original sample weight.