after  expiration day how long flour can be used
There are no legislated expiration dates for flour in fact dry goods like flour, sugar and even pasta rarely have more than an encoded date. In the case of most flours there is nothing to spoil so it does not expire. The exception being the higher the fat content the shorter the shelf life. An example is whole wheat flour. If you are not going to use whole wheat flour within a couple months from purchase then you should store it refrigerated in a tightly sealed container.