If I used expired Alpha Amylase for a NDF assay, can I re-run the bags or do I have to start over?

Amylase is utilized to help digest the starch in the sample. Even using expired Alpha Amylase, it is highly likely the non-starch components, as well as most of the starch, are gone.  

Put the Filter Bags in a 1 L beaker with 80 °C water and 8 ml of fresh Alpha Amylase and allow the bags to soak for 20-30 minutes. This should remove any residual starch. If you have a Fiber Analyzer, you could put the bags in the bag suspender, place them in the instrument with the heat off (you don’t want boiling water) and turn on the agitation. After 20-30 minutes, rinse the bags once for five minutes, dry, and weigh.