Modification is the process by which, during malting and mashing, enzymes in the grain break down large protein chains into smaller proteins and amino acids, making these available to the yeast, removing them from the finished beer, and releasing starch from the grain's endosperm.
 The Importance of Modification
In unmalted grain, the starch which will eventually be converted to sugar and fermented is stored in the grain's endosperm, a mixture of starches and complex proteins. Modification breaks the proteins in the endosperm up into smaller proteins and amino acids. This achieves a number of goals:
- It releases the starch, making it available for conversion to sugar by diastatic enzymes
- It keeps the longer protein chains out of the finished beer, where they can cause haze
- It makes free amino nitrogen available to the yeast as a nutrient
 The Modification Process
 Modification in Malting
Modification begins in the malting process. The germination of the plant triggers the release of the proteolytic enzymes which carry out the modification. Modern base malts have uniformly high levels of modification, and therefore no additional steps are generally needed in brewing with them.
 The Protein Rest
Less modified base malts traditionally had their modification completed in the mash through the use of a protein rest, which is designed to allow the proteolytic enzymes to complete their work. This is still needed with some specialized malts which are intentionally undermodified to add body to the finished beer.
 The Danger of Overmodification
Performing a protein rest on a modern, highly-modified malt runs the risk of overmodifying the malt. While too much protein can result in a hazy beer, too little can result in a light mouthfeel and lack of body. Most malts available to homebrewers do not benefit from a protein rest.