Several bread recipes that I have been looking at recently call for rye malt.
I know that malt is sweet but what other effect will malt have on a bread recipe?
Malt syrups and powders come in two forms, Diastatic and Non-Diastatic. The Non-Diastatic kind is just sugar, and is only useful for adding a little sweetness and flavor.
Diastatic Malt Syrups and Powders are made by taking grain (usually barley, but others can be used, like rye), allowing it to sprout, then toasting it lightly to halt the sprouting process. The little roots and stuff are rubbed off, and the grain is ground into a powder, or soaked into a syrup. This is very similar to the process used to convert grains for beer-making.
The syrup is rich in enzymes that are created by the sprouting grain, for the purpose of converting the seed's starch reserves into sugar for the young plant. Non-Diastatic versions have these enzymes deactivated by heat, leaving the syrup "inert".
The enzymes and sugars do three important things
Here is an article on malt syrups and powders and how to make them yourself: http://artisanbreadbaking.com/flour/malts/
And King Arthur Flour sells a version of the powder, along with some recipe examples: http://www.kingarthurflour.com/shop/items/diastatic-malt-powder-16-oz