- You've probably already heard a lot about hops, IPAs, fancy craft beers, but those topics, they've been done a lot.

So today, let's mix things up a bit.

I'm Sheril Kirshenbaum, and on this episode of Serving Up Science, we're going to explore the science of beer foam.

And for those skeptics, this is totally legit chemistry.

Beer foam, also called beer head or collar, that's the collection of frothy bubbles that create the top level of freshly poured beer.

(upbeat music) Mm.

Foamy.

The bubbles are carbon dioxide gas, which are created both as a byproduct of fermentation, the process by which we get alcohol, and through carbonation where pressurized CO2 gas is dissolved into the liquid at high pressure.

Need a napkin.

In sodas you can see that the bubbles dissolve very quickly.

Not quite as pretty.

In beer, they form the characteristic attractive foamy layer at the top of the glass.

Oh, oh dear.

Joining me in the kitchen today is Chad Rogers, who's been brewing out of Diamondale, Michigan at Dimes Brewhouse.

(camera clicks) (up-tempo lo-fi music) Chad, welcome to Serving Up Science.

- Thank you, Sheril.

- What can you tell us about the bubbles that were before us?

Let's move this over here.

- [Chad] So what we call the head of foam is maintained because of gas bubbles are coated by a proteins, which have hydrophobic and hydrophilic ends.

Those hydrophobic ends cling to the CO2 as it rises through the beer, settles on the top layer, and forms a film of protein.

- I think we need another example, so let's pour a cold one and talk about the foam.

- Absolutely.

(air hisses sharply) Beautiful sound.

So the foam that we're seeing here is CO2 coming up through the beer and attaching itself to proteins that are in solution, coming up to the surface and forming this nice head of beer that we see before us.

- You poured a really nice head on that beer.

Is there a technique to do that?

I was making a mess before.

- So generally, what you wanna do when you pour the beer is you wanna limit the amount of energy that you put into the beer while you pour it.

So to do that, you tip the glass on its side, and you pour the beer at an angle into it.

- Like about a 45 degrees?

- 45 degrees, yep, and let the beer run down the side of the glass and fill the bottom, and then come up from the bottom.

So now how long the head lasts depends on a number of factors.

The primary factor is how long is the protein chain that is inside the beer itself?

So the shorter the protein chain, the less stable the head formation is.

The longer the chain, the more stable the head is.

- [Woman] I didn't know that you were so sciencey.

- Yeah, I know, at first glance, boy, that guy doesn't know anything.

(Sheril and woman laugh) But then he starts talking about sciencey things-- - You know what I mean.

- He's got his fancy chemistry shirt.

- Yeah, just wears a shirt and shows up.

- Well, that's the thing.

In chemistry-- - I'm so happy you wore that.

Now I think most people don't recognize that beer isn't just a bunch of carbs.

It's really got that protein, and that protein plays such an important role in the beer foam that you get.

- The protein is coming from the malt in the grains that we're using in the brewing process.

So that malt contains proteins, it contains carbohydrates that are broken down into sugars, and all those components come together to give us this wonderful product that, as you pour it, the CO2's interacting with that protein, rising to the surface, and creating this head.

- So it has that nice, is it called effervescent, that nice way of wafting up?

- Yeah, it just bubbles up into your nose.

- Mm-hmm, that it definitely does.

What's all this fuss about nitro beers that use nitrogen gas instead of CO2 in the carbonation process?

- You can add different gases to beer for different effects.

So traditionally, it's CO2 is added to the beer, and that's called carbonation.

If you add nitrogen to it, it's generally called nitrogenation, which is a bit of a mouthful.

All right.

(beer can hisses and snaps) - [Sheril] So does it makes a big difference in how that beer foam forms?

- [Chad] Absolutely.

So with the nitrogen being less soluble than the beer itself, forms much smaller bubbles, and you get a tighter, more stable head.

- [Sheril] Oh yeah, looks a little different.

It's bubbling up.

- What that is is the CO2 and the nitrogen mixing together.

The CO2 is dropping, and the nitrogen is rising.

And it's giving you this really stable head that's forming.

Now the reason that it's so stable is because there's more nitrogen in the atmosphere, so there's less reason for the nitrogen to leave the bubbles.

- So it's a nice accent - Yes.

- to your drink throughout.

- It adds mouthfeel to the beer.

- Tell me about mouthfeel.

What do you mean by mouthfeel?

- So mouthfeel is, in general, how the beer feels in your mouth.

- [Woman] (laughing) Sorry.

(everyone laughing) - Huh!

- Is that too much?

- [Man] So not how it feels in your pocket.

(everyone laughing) - [Woman] (laughing) Tell me about mouthfeel.

- I guess we're not using mouthfeel.

I don't know, could it be grainy, could it be smooth?

- [Man] That's it, that's it.

- And that's nitrogen.

- Cheers.

- Cheers.

(glasses clink lightly) (chime dings) Boy, that's a mess.

- Here you go.

Well, I see you also brought this glass that I don't think I don't wanna drink from.

It's kinda dirty.

- Yes, that's a dirty glass.

(camera clicks) Another aspect of beer foam is how clean your glassware is.

So if you have soil on your glassware, it will cause premature foaming, foaming around the edges of the glass, the inside, which is, again, what you don't want.

- [Sheril] So by soil, it could be soap or even chapstick or lipstick.

- [Chad] Chapstick, things that are oily.

- So gross, Chad, ugh.

(people laugh) - [Chad] I'm looking at the sides and yeah, it's definitely dirty.

- Zero tip for that.

(people laugh) - Yeah, see how it's breaking up right here?

- Yeah.

Oh, can I turn it for you?

Tell me more about nucleation and how the bubbles form as I sip this lovely amber ale.

- So an example of nucleation is if you take a beer.

I have some rice here.

So what you can do is you can add rice or anything, really, to a beer and create nucleation points.

So now you can see in the bottom of the glass, you're getting CO2 released.

- Yeah, let's put some more in there and make it a party.

- So what's happening here is CO2 is reacting with the, there we go, with the rice, and it's being released from solution.

- Nice.

And look, we're adding to the foam at the top.

I didn't expect it to get that high.

Well, thanks so much, Chad, for coming.

For thanks, thanks.

Thanks so much for joining me, Chad.

- Thank you, Sheril.

Cheers.

- Cheers.

(upbeat music) (chime dings)