Starch and crispy potato

Imee_34011

I read in modernist cuisine that starch helps make thing crispy. Makes sense since many fried food are first coated in flour before frying. So I would like to understand why when making fries, potatoes are rinsed first before cooking to remove starch. Heston Blumenthal fries have you first boil the spuds till breaking apart then drained(not rinsed). The purpose is to allow the starch in the spuds to be released and coat the potato so that when the get fried, it will be crispy. Also read somewhere in ATK that on boiling spuds in water with baking soda(softens cell wall) to allow the starch within the potato to be released before frying.

So why soak and rinse potato to remove the starch?

Thanks

GaryT_92514

Yeah, Im struggling with this too. My understanding so far is that it is the form that starch takes. Cells contain the starch granules, which in turn are made up of their constituent components (amylose and amylopectin). Cutting the potatoes damages the granules and releases the amylose/pectin. In this form starch is the enemy (this is what makes up starch glues, think wallpaper glue). So the rinsing removes the damaged starch granules, leaving the undamaged to crisp up. Not sure about this interpretation though, I will be interested to hear what the professionals say... the Ideas in Food book describes this process...