Yum....chemistry of flavours

As chef Tristan started his cake and sausages cooking on the Naked Scientists BBQ, Katie Haylor asked chemist Jane Parker about the science of flavour...

Chris - Right Tristan I suppose you've now got the tins full. So you've got greaseproof paper lining the tin, there's the piece of pineapple in the bottom with the cherry. Spoon the mixture on top, and now what are we doing?

Tristan - So we use the tin to bake the actual pineapple upside down cake. I've lined it carefully with greaseproof paper, popped up on the grill, so there's intense heat coming from underneath it. And we're going to pop the lid down, let it bake essentially.

Chris - You've also got them on there alongside the sausages, you're cooking up some nice sausages. We're not going to get sausage flavoured upside down cake though?

Tristan - Maybe this is a new thing, who knows? I think we'll get some of the smoke from it. And that's a really important part of the flavour and all this sort of stuff. But it's one of those sort of crazy days with pineapple upside down cakes, sausages, and cake, and cooking in the rain, right?

Chris - It's already smelling really delicious. Katie get a quick whiff of this down the mic...

Katie - Oh haha! I'm so jealous!

Chris - I mean this is the sausages. Oh, it smells amazing, I'm telling you!

Katie - Jane, you're a flavour expert. Before we, well, before they get to try some of this delicious food, what exactly is flavour? Are we talking smell, taste?

Jane - Well all these words - flavour, aroma, taste - all get a little bit confused in the English language and as scientists, we've got a clear distinction between them. So taste is what you perceive on the tongue. So that's things that are sweet, sour, salty, bitter, and umami, which is the savoury taste. And aroma is what you perceive in the olfactory bulb through your nose. And these are very volatile compounds. The combination of these is what we describe as flavour. And as Barry was alluding to earlier it's flavour, aroma and taste, but it can also be colour and texture and sound and other things as well.

Katie - But how will those pork cylinders that they've put on the barbecue, how will they translate to sausages in their brains? What's going on?

Jane - Well, to start off with as you start cooking the sausages you've got changes in the protein structure as it denatures and aggregates again to tenderise. And you've got colour formation, but the key thing is the flavour that's developing. And there's four different ways that you can develop flavour while you're cooking sausages. And one is the Maillard reaction that's very well known, and it's the reaction that occurs between proteins or amino acids really and sugars as you heat things up. And that gives you these roasty, toasty, and meaty aromas. Fats - they start to degrade as well. And when they degrade, they release aroma compounds. And these help you work out whether it's a beef sausage or a lamb sausage or a pork sausage, because they give you that ‘species’ character. These go on when you're cooking meat anywhere, but once you're putting things on the barbecue, you're starting to get caramelisation as well. So that's when the surface is really hot. And if you've marinaded your pork sausage in anything sweet and sticky, you'll get even more caramelisation going on. And the final thing is the flavour that comes from the charcoal itself. The charcoal is made from wood, wood contains lignin, and there will probably be some remnants of lignin in your charcoal. And as you burn the lignin you generate a lot of smokey and spicy compounds, which are phenols and glycols, and you can even get vanilla as well. So you can get quite a fragrant aroma. And we've got some sunshine over here and that's a smell that's coming in through my window as my neighbours are barbecuing. It's definitely that smokey element that gives the key barbecue element to your sausage.

Katie - It sounds delicious. I really wish I'd had some dinner before the show. I think Chris' barbecue, is it gas, Chris?

Chris - Yeah. I was just listening to what Jane was saying and thinking: oh dear! Because I've subjected Tristan to cooking on gas, is that bad? He's shaking his head and he's rueing the day.

Tristan - It's a little bit of a faux-pas to be honest.

Chris - Ah sorry Tristan! So is that a problem, Jane? Can I get away with this?

Jane - I think you can get away with it because you've got the high temperatures. You've got the Maillard, you've got the flavour from the lipid and you've got the interactions...

Tristan - I almost went home!

Chris - It's a no from Tristan Jane

Jane - Oh dear. I'll leave. I'll go home!

Tristan - I'm a temperamental chef!

凯蒂-哦亲爱的!

Tristan - It's alright, I think actually it works because you've got the fats hitting the flame and the flames are licking the outsides of the sausages and stuff like that. So it works. But there is a little smokiness that you get from the charcoal, which is something really special.

Katie - Chris, I'm rather jealous.