Here, check this out. This is an article explaining at length how to make perfect French fries.
How to make perfect McDonald's style French Fries
So basically, you have to cut your fries so that they are 1/4 inch thick an then blanch them in boiling vinegared water (1 tablespoon per quart of water) for about 10 minutes. This has to be done to keep the balance between pectin, starch and simple sugars. Potato cells are held together by pectin (a form of sugar) and contain starch granules. When the cells come in contact with heat and water, pectin starts to decompose into simple sugars, which exposes the starch granules, which in turn release the starch they contain. Too much sugars and the fries become to brown, to less starch and your fries won't have a decent crust, and so on. Therefore balance is important. Now, putting the fries into hot water serves two purposes: rinse off excess sugars and activate an enzyme that strengthens the pectin, giving the fries a firmer and more intact structure. Problem is, this enzyme woks better the higher the water temperature, but stops working altogether above ~170 degrees Fahrenheit. But here comes the vinegar: acid slows the breakdown of pectin.
Step two is deep-frying the fries in 360 degrees Fahrenheit vegetable oil for 50 seconds.
Step three: freezing the fries overnight or longer. This helps make the interior of the fries all the more fluffier. By freezing, all the excess water inside the fries gets converted into ice crystals which damage the potato cells and make it easier to then become expelled as steam in the last frying step which is...
Step four: deep-fry the French fries in 360 degrees Fahrenheit vegetable oil for 3 1/2 minutes, drain them, season them and serve them immediately.