Roast the crab shells at 400 degrees Fahrenheit until they become brittle.
Place crab shells in a large plastic bag (1 gallon freezer bag works best) and with a mallet or similar object, crush the crab shells.
In a large pot, sweat the carrots, onions, celery and garlic until soft.
Add in corn cobs and crab shells.
Stir all ingredients and turn up heat to medium high and add in bottle of IPA.
Cook for 3 minutes and then add in water.
Turn heat down to a simmer and allow mixture to reduce for about 45 minutes (mixture should reduce by about 1/3).
Strain through a fine mesh strainer (use cheesecloth if you have it in order to eliminate shells).
Cool and store in labeled container.