- Have you ever bitten into an apple.

That's not quite ripe yet and experienced that dry, puckery taste and feeling?

Do you know what it is?

I'll give you another hint.

It's 11:00 a.m.

I'm Sheril Kirshenbaum and on this episode of Serving Up Science, we are talking tannins and their role in your glass of wine.

At some point you've probably heard a waiter allude to tannins.

So what are they anyway?

Tannins are naturally occurring plant polyphenols that are all over the place from the skins and seeds of grapes.

Mm, grapes.

To the oak in wine barrels.

This is a nice cab.

I don't have a pull tab, okay.

We hear about tannins most frequently in reference to wine but in reality they're everywhere.

I like that I get to eat on this show so much.

You'll encounter tannins in chocolate, coffee, walnuts, red beans, cinnamon, and, well, nature.

You don't get this with boxed wine.

Tannins even contribute to the beautiful colors found in flowers and autumn leaves and have ya ever noticed a lake that looks a little bit like tea?

When tannins leach out of plants, they can seep into groundwater or lakes and streams and make them appear brown.

It's growing on me.

Think of them as a natural deterrent to herbivores, those little critters that eat plants and that ranges from insects to birds to reptiles to us.

They increase in concentration when plants are under stress and their astringent taste is nature's way of encouraging everyone to move on and graze elsewhere.

The potent chemicals are also said to fight off microbes and fungi and protect the plant from UV rays.

Tannins work by deactivating proteins and we've known about them for a really long time 'cause we've been using this denaturing superpower to tan animal skins and make leather goods impervious to bacterial attack or rotting.

Whoopsie.

There's a snake in my boot.

In fact, the word tannin comes from the old German word, tanna, meaning oak.

I'm gonna say that again 'cause I have to kinda say that quickly 'cause I'm not sure how to actually pronounce the word.

We're gonna get someone like calling like it's pronounced tanna.

The practice has been around for thousands of years dating at least as far back as Ancient Egypt.

It was popular in, (mumbles), I can't speak today, I'm sorry.

It was also popular in Ancient Greece, Rome, and China as well.

Using tannins from willows, sumac, maples, eucalyptus, and other plants to tan hides.

But it's just over the last few years that botanists are finally understanding more about the science behind the plant cells responsible.

Do you remember your cell biology from high school?

Our producer doesn't.

So here's a visual.

Right there or right there or somewhere in this vicinity.

Those little round circles are the vacuoles.

They're tiny storage bubbles found in cells that hold onto things the plant may need to survive but also things that need to be sealed off from the rest of the cell, whether they're food, waste, or the protein denaturing chemicals in tannins.

Well, you could go down.

Do you wanna do this whole part again?

- [Producer] Oh, sorry.

- I'm Ron Burgundy.

- By keeping tannins at bay in vacuoles, they don't interfere with or even accidentally kill the cell.

Tannin-y.

We most often hear about tannins when we talk wines so we'll move in on that topic.

In wine, tannins contribute to the color, bitterness, and aging capacity.

They're the reason for that astringent sensation that wine connoisseurs often describe as desirable.

- I like the wine and not the label.

- And that initial puckering taste when you sip a red actually comes from tannins.

Sometimes even from inside the wood of the oak barrels where your wine was stored for aging.

- Let's splurge, bring us some fresh wine.

- Just like with that unripe apple, the astringency is meant to be off putting.

But in the right concentrations, tannins also lead to the complexity of wine that so many people enjoy.

It's kinda sharp.

So if you wanna impress your friends at the next dinner party, bring up tannins and see how many of them find tannins as effective as I do.

Cheers to camera A.

Cheers to camera B.

Is that camera B?

(upbeat music)