Making gravy involves using the drippings from a roast, deglazing the pan with water or stock and seasoning the liquid to taste. Salty gravy can ruin an otherwise good roast, whether over seasoned by the cook or made with a too salty stock. One well-known method of rescuing gravy is to put a potato in the boiling liquid for 20 minutes. In theory, the potato will absorb some salt. This particular theory, when tested by chemistry Professor Emeritus Robert L. Wolke of the University of Pittsburgh, failed. However, there are other remedies a cook can attempt to rescue salty gravy.
Add a small amount of sugar to your gravy and allow it to absorb as the gravy simmers. Start with a 1/2 tsp, and test the gravy after a few minutes. Keep adding sugar in small increments until the salty flavour diminishes.
Add 1 tsp of unsalted butter to your gravy. According to researchers at Exploratorium, fat coats the tongue, and the salty taste will be less prominent.
Add 1 tsp of cider vinegar to neutralise the gravy. Let the gravy come to a simmer, and then taste it. Keep adding a little at a time until you have reduced the salty flavour. As with the sugar, don't add so much that the gravy tastes like vinegar.
Add more liquid to your gravy. If you prefer thicker gravy, make a roux first by melting 1 tsp of butter and mixing it with 1 tsp of flour. Add 2 cups of water or stock to your roux, stir it in completely and bring it to a boil. Let it boil for at least five minutes, first to thicken up, but also the longer the boil, the less floury taste it will have. Add this mixture to the gravy once thickened and continue to simmer the gravy for a few minutes.
Use homemade stock that is low in salt whenever possible; store-bought stock tends to be over seasoned. When adding sugar, keep in mind, you're not covering the salty flavour, you're simply adding another flavour to make the saltiness less prominent. Add enough sugar to cut the salt, but not so much that your gravy will end up tasting sweet. When adding more liquid, add water if the stock was the salty culprit. If your seasoning was at fault, add more stock, if available.