Once you have verified your Identity with the IRS, you need to enter a PIN or Signature PIN to sign your 2014 tax return. You can create this 5 number signature PIN on your own. Detailed instructions on how to enter your Identity PIN and/or AGI on efile.com.
Fats or oils (also generally called fats) are added to foods, like crackers, cookies, and cakes, to improve the taste and feel (texture) of foods. Foods become rancid when there is a chemical change to the fats in the food. There are three types of rancidity: hydrolytic, oxidative, and ketonic.
The smell is of rancid fats in the flour. It is a very distinct smell, but hard to describe. I would agree that sour is part of it. The best way to learn is by comparison. Smell some fresh, clean flour and remember what it is like. Any kind of unpleasant odor than that is rancidity. You may have smelled it also if you opened a box of cereal that has been around too long, or even poppy or sesame seeds-anything with fats that sits around at room temp will eventually go rancid.