How much extra salt?

February 20, 2011 9:57 AM

Chemistry, math nerds, and smart people please help me with this cooking question involving salt.

I am making a soup for a LOT of people tomorrow. I am using store bought "Kitchen Basics" vegetable stock as my base for the soup. Here is the problem:

As I practiced this recipe, I always used the "original" variety of the stock which has sea salt as an added ingredient. When I went to buy all the boxes for my party, the store only had the "unsalted" variety which has no added salt.

I need to make the "unsalted" variety taste just like the original variety, since the amount of salt was perfect.

In a serving (240 ml) of the original variety, there are 330 mg of sodium. In the same size serving of the unsalted one, there are 240 mg of sodium, thus there are 90 more mg of sodium in the unsalted one.

Does it then follow that I will need to add 90 mg of table salt to make the unsalted equal to the salted for a serving? If not, how many mg of salt would I need to add for each serving. I have access to a very good scale I so I will be able to measure this out precisely.

posted by anonymous to Food & Drink (12 answers total)

Honestly, I wouldn't worry about the exact weight. You're making soup, not media. Salt to taste - put in a healthy pinch and then add more if it doesn't taste salty enough to you.
posted by maryr at 10:00 AM on February 20, 2011 [6 favorites]

@maryr has it--don't try to calculate the amount of missing salt and then replace it. Just undersalt to begin, add and taste, add and taste, until you like it.

Always err on the side of undersalting, because people can add more at table and oversalting is incredibly difficult to alleviate satisfactorily.
posted by thinkingwoman at 10:03 AM on February 20, 2011

And make sure you give the salt time to dissolve and mix before tasting. Good luck!
posted by iftheaccidentwill at 10:05 AM on February 20, 2011 [1 favorite]

If you want to be exact and add 90 mg sodium, look at the nutrition facts on your table salt to see how many mg of sodium are in one tsp (or whatever the serving is) and use that to figure out how much to add.

The standard Morton's Iodized Salt has 590 mg sodium per 1/4 tsp so you would need to add ~0.13 tsp to get 90mg...the closest measurement you probably have would be 1/8 tsp.

Also, if you are interested, what they call "sodium" is really sodium chloride. Elemental sodium is a metal and catches fire in water.
posted by stevechemist at 10:07 AM on February 20, 2011

To answer your question more directly, there are only 0.393 grams of sodium per gram in table salt, so do your math accordingly.

But in all seriousness, just salt to taste.
posted by sindas at 10:11 AM on February 20, 2011

Two problems with a straight-up analytical chemistry approach here: one is that "sea salt" is not pure sodium chloride but also contains KCl and whatever else is floating around out there. The other is that mg sodium =/= mg salt. Table salt (NaCl) has a formula weight of 58 g/mol, whereas sodium alone is 23 g/mol, so you need to add more weight of NaCl to get the equivalent weight of sodium.

So here's my calculation:

NaCl is 23/58 = 40% sodium by weight (close enough)

To get 90 mg of Na you need to add 90 / 0.4 = 225 mg NaCl (close enough)

Per 240 ml serving you'd need to add 0.23 g salt.

But as I said, sea salt is not pure NaCl (and it also tastes a little different - less salty, to me). You can get a rough idea how much you need to add, but I'd start with less and "titrate" up by taste. Call it organoleptic analysis if you want to get geeky.
posted by Quietgal at 10:15 AM on February 20, 2011 [1 favorite]

As others have noted, just add the salt to taste at the end.

Also, why on earth is this anonymous?
posted by dersins at 10:38 AM on February 20, 2011 [9 favorites]

It's soup. Taste and correct seasoning as desired.
posted by Sara C. at 10:55 AM on February 20, 2011

What Quietgal said- sea salt is not pure NaCl. Speaking as a chemist and a cook: salt it until it tastes good.
posted by Green Eyed Monster at 12:32 PM on February 20, 2011

Yeah, don't worry. Just make your soup with some salt and then add as needed. I also disagree about undersalting. Salt enhances other flavors. Don't hold back.
posted by serazin at 12:35 PM on February 20, 2011

Definitely don't add the same amount of salt that was in the original stock, even if you can calculate it. Low sodium varieties of soup stock usually have some other ingredient that replicates some of the saltiness flavour, e.g. lemon, or nutritional yeast or similar. If you put "back" that 90 mg of salt, you are likely to end up with something that tastes over-salted.
posted by lollusc at 2:44 PM on February 20, 2011 [1 favorite]

Use exactly one one-ounce slice of bacon per box of soup.
posted by novalis_dt at 4:08 PM on February 20, 2011 [2 favorites]