From the brains behind brains on, this is the moment of um.

Answering those questions that make you go, um, um, um, um, um, um from APM studios. I'm Anna Weggle. It's a whole thing, watching videos of babies, trying a lemon for the first

time. Those innocent, trusting little humans, look at the bright yellow fruit, wide-eyed and excited.

They open their mouths, take a taste, and wait for it. Squish their face into a tiny dissatisfied mess of a

disappointed human thinking, why? Why would

you do this to me? Babies react this way because lemons are sour. Eaton on their own, they taste

so tart that they can make people squint their eyes and recoil. But is there something more sour

than a lemon? Hi, my name is Elie, and my question is, what's the sourest thing in the world?

The sourest food in the world is the Umaboshi plum.

Other sour foods that you'll recognize are vinegar, lime juice, lemon juice.

My name is Janelle Klepper.

I have a master's of public health and Nutrition from the University of Minnesota.

We're really good at detecting things that are sour

because things that are sour might be too acidic for our bodies

to do damage to our tissues or they might be spoiled

and something that we shouldn't eat that would make us sick.

Sourness is detected by acid content in food and we can measure those on the pH scale.

A pH scale runs from 0 to 14 with 7 being neutral.

Things that you'll recognize in food are water and bananas. They have a pH

of about seven. One change in the number from seven to six means that something that's six is

ten times more acidic than what it's at a seven. Sour foods will register lower numbers and the

umumbo shi plum registers at 2.8 on the pH scale.

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