We’ve all tasted utterly sour foods. Which of these do you consider the sourest?
I have one unquestionable answer: Bilimbi (Averrhoa bilimbi)
I have one tree of the species and we use it in cooking all the time, but when we’re feeling daring, we sometimes take and eat one raw. The smaller ones are a bit fine, but the large ones are so sour the socket of the jawbone starts to tense painfully! For a few seconds you start feeling a bit lightheaded as well.
That looks like a plump version of the sour starfruit (same genus) fruit that’s popular in Vietnam as a garnish for foods.
there is something a small fruit which is called kakaronde in our regional langauge they are used for makeing sabzi
Swamp cranberry perhaps if we don’t take lemons and other citruses.
I’ve tasted many sour fruits but I definitely agree with your answer. Especially bigger ones are very sour. Locally they are sometimes eaten with salt and are used for cooking many food. And as I type this a similar feeling is coming to my tongue 
(I don’t know to exactly explain it in English).
Yes, I have familiarity with salt-and-chilli served fresh Bilimbi…
I feel it too, a slight salty tingle (and a rather electric feeling sort of like those Center Shock gum sold in small local shops)
And the herbal broth (in Tamil Language it is known as Rasam) that I had this very afternoon came with small bilimbis in it.
Wild apple (Malus). It is so sour that last time I tried it, I’ve got acid burn in my mouth. Could not eat anything except mildest soups and porridges for two days.
I caught a plain-bellied water snake once that proceeded to bite me multiple times, I can’t say for its taste but that was definitely the most sour thing I’ve ever seen
That seems utterly terrifying!
Well, my story is more about bitter fruit than sour. I’m sharing it only so no one repeats my mistake.
Once while on a winter hike with a plant ecologist friend of mine we came across a Bittersweet (Celastrus) vine laden with berries. I commented on the common name— bittersweet— and asked my friend if he had ever tasted the berries to confirm if they were, in fact, bitter and/or sweet. He had not. We decided to throw caution to the wind and so we each chewed on a bright red, ripe-looking berry from the plant. The taste was so powerfully vile and medicinal and just plain nasty that we spent the next five minutes spitting out as much of the horrific flavor as possible.
Was there any sweet in the flavor?
Not a bit! Just pure, evil bitterness. I’ve never observed wildlife eating the conspicuous berries in the winter and have to wonder if animals also taste something noxious in the fruit.
If you ever ate too much pineapple you probably got the same results, acid in both is very high, but at least with pineapple it’s a sweet pain!
Yes, indeed. Especially that it was maybe two bites at most.
Good one
Fruit of the wild Himalayan Seabuckthorn is definitely among the sourest things I have eaten.
Though I cannot say anything about the different Sour Grapes I may or may not have had.
Unripe, wild persimmons are beyond sour, inedible. However, after the first freeze of the autumn deer relish them.
They call that astringent! Makes your mouth dry right up. It’s a clever adaptation to keep the fruit from being eaten before it’s ripe and the seeds are ready. Ripe persimmons are so great though.
I found out relatively recently that the astringent japanese persimmons you sometimes find at the grocery store are actually delicious if they’re prepared properly first. They need to be cut or peeled and then left to air dry until they’re almost completely mushy. The tannins that cause the astringency break down during drying and the fruit is actually incredibly sweet.
With pineapples it’s primarily the enzyme activity rather than the acid content that can cause tissue damage. I love the dense pineapple cores especially, so I’ve definitely experienced that one first hand, too. Did you know they actually breed genetically modified ones that lack that the particular enzyme that causes that to happen? The modified pineapples are actually pink inside instead of yellow as well.
Edit: I looked up the genetically modified pink pineapples again. While they do have less bromelain (the enzyme primarily responsible for causing tissue damage when eating), apparently the color change was due to modified amounts of lycopene (responsible for the red color in fruits like watermelon) and beta carotene (responsible for the orange color in carrots). So the different color is the result of a different modification than the reduced tissue damage.