What is enrichment?

The FDA definition of enrichment is “the adding back of nutrients originally present in the food that have been lost as a result of processing.”  During the processing of wheat into flour, 40% of grain (mostly bran) is removed.  Many of the plants’ nutrients (B vitamins, iron) are in the bran.  When the bran is removed to produce all-purpose, bread, and cake flours, many of the  nutrients are removed with it.  To compensate for that loss, thiamin, niacin, riboflavin, and iron are added to produce enriched flour. Laws in the United States require "enrichment" of processed wheat flour with vitamins B1, B2, B3 and iron in order to compensate for some of this loss.
 

Folic acid and calcium can also be added. 
 
Source(s):
accessdata.fda.gov. “Code of Federal Regulations - Title 21: Food and Drugs. “Standard of Identity - Enriched flour.”