Salty gravy can ruin an otherwise good roast. One well-known method of rescuing gravy is to put a potato in the boiling liquid for 20 minutes to absorb some salt. However, when chemistry Professor Emeritus Robert L. Wolke of the University of Pittsburgh tested this theory, it failed. Here are some tricks that do work.
Add a small amount of sugar to the gravy and let it simmer. Start with 1/2 teaspoon, and test the gravy after a few minutes. Keep adding sugar in small increments until the saltiness diminishes. Add enough to cut the salt, but not so much that the gravy ends up tasting sweet.
Add 1 teaspoon unsalted butter to the gravy. According to researchers at Exploratorium, fat coats the tongue, and the salty taste becomes less prominent.
Add Apple Cider Vinegar
Add 1 teaspoon apple cider vinegar to neutralize the gravy. Let the gravy come to a simmer, and then taste it. Keep adding a little at a time until the saltiness is reduced. Don't add too much or else the gravy will taste like vinegar.
Add More Liquid
Add more liquid to the gravy. If you prefer thicker gravy, make a roux first by melting 1 teaspoon butter and mixing it with 1 teaspoon flour. Add 2 cups water or stock to your roux, stir it in completely, and bring to a boil. Let the mixture boil for at least 5 minutes to thicken it up and neutralize the floury taste. Then, add it to the gravy and continue to simmer the gravy for a few minutes.