Maybe you forgot to use low-sodium broth. Maybe you forgot that you were using something salty like bacon or ham in your soup and you threw in an extra pinch of salt. In either case, you now have a pot of too-salty soup — I was guilty of this just last night when making a big pot of turkey meatball soup, but luckily it was flavorful enough that I could dilute it with water.
But what happens when you like the flavor of the soup and don't want to change it, but it's just too salty? Can you throw a potato into it to absorb some of the salt? We put this tip to the test to see if it really works.
The Original Tip
The theory is that a potato is the perfect vehicle to absorb excess salt. Just throw it into the pot and simmer it for awhile, remove it after it's absorbed some of the salt, and you're left with less-salty soup. No need to add more liquid or other ingredients to help disperse the extra salt.
It was hard to find any consistent suggestions for a ratio of potato to soup, but the common advice was to simmer but not overcook the potato in the soup, and the time frame suggested was usually about 30 minutes.
The Testing Method
I tested this tip with boxed chicken broth since it was already seasoned and convenient to test with. It also had a pure, clean flavor so that any potato flavor that leaked into the broth would hopefully be noticeable.
I opened 1 quart of chicken broth but set aside 1/4 cup so that I could taste and compare the results with the original. After I brought the remaining 3 3/4 cups of broth up to a simmer, I dropped in 1 medium Yukon Gold potato that I had cut into 1/2-inch pieces, figuring more surface area would be good at absorbing more salt, then let the whole thing simmer covered for 30 minutes (I didn't want to lose any liquid through evaporation so I kept it covered).
After 30 minutes, I removed the potato and let the whole thing cool down until it was the same temperature as the 1/4 cup of broth I had set aside. Since temperature can affect how your taste buds detect seasoning, I felt it only fair to taste the two broths at the same temperature.
The results were subtle. The potato broth didn't seem much less saltier than the original broth, but it definitely had lost some of the strong chicken flavor and didn't seem as intense. The potato broth definitely did not taste like a lot of salt had been extracted out of it.
Out of curiosity, I took a bite of the potato, and it tasted like, well, potato cooked in chicken broth. It wasn't overly salty and definitely had absorbed some broth as well as the salt in the broth, but it wasn't a clear fix for this soup. It's also good to remember that even as the potato is absorbing soup and a little of the salt, it is contributing starch, which might not be desirable if you have a clear soup that you don't want clouded or thickened.
Verdict: This is not a mind-blowing tip.
While your best bet it to not oversalt your soup in the first place (season slowly as you go and do it in small amounts), overseasoning does happen to the best of us. While this test proved that potatoes don't do a good job of just absorbing excess salt, it does remind us that adding extra ingredients, like rice, pasta, vegetables, water or more low-sodium broth can be tasty additions that can help absorb the extra salt.