According to George Greenstein's "Secrets of a Jewish Baker", altus is the secret of good rye bread.
Altus is left-over rye bread which is ground-up and soaked in water.
To make altus, cut the crusts from a loaf of bread(*), soak it in water for several hours, or overnight, under refrigeration. It will keep several weeks under refrigeration. Use small amounts in bread dough, pressing water out of it.
This will intensify the taste of the rye bread and make it a moister bread. You will have to adjust the hydration of your dough when you use altus, probably adding a bit more flour or a bit less water.
(*) There's always a "but" in every set of baking instructions. Jeffrey Hammelman has a great sourdough flax seed rye bread in his cookbook. When we made it at Camp Bread 2007, Jeff didn't bother cutting off the crusts. He soaked the bread overnight with the flax seeds and dropped the glop into the next day's dough. The skeptics in class were worried that there would be chunks of old bread and crusts in the new bread. Jeff assured us we'd never notice the bread or the crusts. He was right. He also told us that if you have no rye bread, you can use a dark wheat bread. Any bread, he told us, but the darker the better.