What's going on in my mouth?

July 16, 2010 4:20 PM

Calling all cooking chemists: It's said that the tartness of food indicates it's acidity. And sugar can be used to reduce that tartness. But a sugar solution is pH 7, so it's not neutralizing the acid. What gives?
posted by buzzv to Science & Nature (13 answers total)

This isn't chemical, it's neurological.

Unripe fruit has lots of acid but not very much sugar, so we have evolved to find it tart and unpleasant to eat -- because it isn't healthy to eat it. Ripe fruit has lots of sugar, so we have evolved so that lots of sugar cancels out the taste of acid, so that we will eat ripe fruit, which is nutritious.

The acid sensors still react, but when the sugar sensors are going off the acid sensors get ignored.
posted by Chocolate Pickle at 4:29 PM on July 16, 2010

Yeah Chocolate Pickle has it. I mean you COULD add some base to acidic foods to cut that tartness but we taste most bases as really bitter (think soap) so most of the time you are better off with the sugar.
posted by Captain_Science at 4:43 PM on July 16, 2010

we have evolved so that lots of sugar cancels out the taste of acid, so that we will eat ripe fruit

and chocolate pickles.
posted by Westringia F. at 4:53 PM on July 16, 2010

Exactly. It doesn't reduce tartness, it balances it.
posted by gjc at 5:16 PM on July 16, 2010

Am I missing something in your question? A pH of 7 is neutral. Anything that is acidic has a lower pH ostensibly down to 1. Adding sugar to an acid solution would make it less acid even if it did not cross over into base.
posted by Old Geezer at 6:18 PM on July 16, 2010

Adding enough sugar to an acidic solution so that it no longer tasted sour wouldn't substantially raise the pH.
posted by Chocolate Pickle at 6:21 PM on July 16, 2010

It's said that the tartness of food indicates it's acidity.

This is wrong. When it comes to our tongues and our brains, "tart" means "acid without sugar". It doesn't mean just "acid".
posted by Chocolate Pickle at 6:25 PM on July 16, 2010

Thank you all very much! Now back to dinner!
posted by buzzv at 6:54 PM on July 16, 2010

As you've seen by now, sugar won't actually neutralize acid. If you want to make a food less sour, you can neutralize the acid with base. There's some in your kitchen cabinet, probably: baking soda (sodium bicarbonate) is alkaline, and a tiny pinch stirred into super-sour lemonade will make it taste less sour without adding sugar. (Don't overdo it, though - too much baking soda will give a nasty metallic taste.)

There are less obvious bases in your food, too. Proteins are made of amino acids, two of which have basic side chains. (Acids with bases attached sounds kooky, I know, but you can read up on protein chemistry if you really want to get your geek on.) These bases will slowly neutralize acids; they don't ionize as quickly as baking soda, but after a while (especially with heating) they'll get the job done. What this means in the kitchen is that your sour tomato sauce will gradually taste less sour as you simmer it in the presence of meat. Vegetarian? Dumping grated Parmesan cheese into it will do the same thing.

One final comment: to me, sweetness doesn't cancel out sourness. If my lemonade is too sour, adding more sugar just makes it too sweet and too sour. Yecch. I guess taste physiology can differ, but I'd like to see more information about sugar suppressing the acid sensors.
posted by Quietgal at 8:44 PM on July 16, 2010

The molecular gastronomist Hervé This has had at least a couple of his books translated into English, and he's a pretty entertaining source on this sort of thing (Where "entertaining" = vaguely geeky).
posted by Emperor SnooKloze at 8:49 PM on July 16, 2010

Unripe fruit has lots of acid but not very much sugar, so we have evolved to find it tart and unpleasant to eat -- because it isn't healthy to eat it. Ripe fruit has lots of sugar, so we have evolved so that lots of sugar cancels out the taste of acid, so that we will eat ripe fruit, which is nutritious.

This is probably super obvious, and sorry for piggy backing, but why are unripe fruits (or any tart foods) unhealthy to eat?
posted by kylej at 10:02 PM on July 16, 2010

As some what of the converse of sugar neutralizing an acid in fruit, I sometimes find that a fruity wine will taste sweet to me even though it has been fermented dry (there is no residual sugar).
posted by MonkeySaltedNuts at 10:10 PM on July 16, 2010

Unripe fruit has lots of acid but not very much sugar, so we have evolved to find it tart and unpleasant to eat -- because it isn't healthy to eat it. Ripe fruit has lots of sugar, so we have evolved so that lots of sugar cancels out the taste of acid, so that we will eat ripe fruit, which is nutritious.

This is probably super obvious, and sorry for piggy backing, but why are unripe fruits (or any tart foods) unhealthy to eat?

I wouldn't say it's not healthy to eat, but that it doesn't do much for us. The complex sugars are hard or impossible to digest and give us the runs or hilarious/uncomfortable gas. So we evolved to sense that unripe things don't taste good, and ripe things do.

Also, fruits evolved along with us. The more delicious the fruit, the more fruit gets eaten and the more seeds get spread around. Unripe fruits contain unripe seeds that can't turn into viable plants. So it stands to reason that the plants with the vilest tasting unripe fruits have the best chance for their seeds to mature and reproduce.
posted by gjc at 6:43 AM on July 17, 2010