 Yikes. That was great. I can't tell you how it feels to be here. Renee, colleagues of Renee's, this has been an amazing event. And of course this is just part of it. I have never in my life thought that I would have the chance to smell 35 varieties of hay. But that's what I did yesterday and I'm really glad I did. If you get a chance as you're leaving, check out the hay. It's amazing. And I'm going to be taking you from the sublime and the poetic what was it just on the table here. Back to school. Sorry. To chemistry class. My justification for that is that what underlies that poetry is chemistry. Plants are the sort of chemical masters of the universe. They're the only creatures there are that can start with rock and air and sunlight and turn those materials into what was just on this table. They're amazing creatures. And what I'd like to do today is tell you a little bit about one small part of their lives. We've been hearing about all different aspects of their lives over the last couple of days. I'm going to focus very much on flavor which is the part of their lives that gives us the most pleasure. And talk a little bit about what science can tell us about the nature of their flavor. Why they have these flavors. Why should we be so lucky as to have these amazing things to nourish ourselves with. And I hope along the way to be able to provide the cooks in this room with a few useful pieces of information. So somewhere around here here. So don't worry I'm going to be flashing molecules on the screen. There's no test at the end. It's just to remind you that this is what it's all about. This is what it comes down to. When we taste something when we smell something when we experience the flavor these are what we're experiencing. Molecules. And I've got just four examples. Water which has no taste or smell right next to it something that looks very similar. Same structure but one atom has been changed. The oxygen has been changed to sulfur. And now you've got something that smells like eggs. Rotten eggs if it's too strong. Nice eggs just a little hint. Acetic acid the smell of vinegar and on the right there molecule of sucrose which is sweet sugar. This is what this is the way we experience plants and foods in general it's the chemical senses. Let's see. There we go. So just a few words about kind of different categories of our nourishment. Fruits are delicious. So what's the recipe for the deliciousness of a fruit? Molecules. And in the case of fruits it's dozens to hundreds of molecules. So this is the recipe for the deliciousness of strawberry. In fact this is only a partial list of the flavor compounds that are found in strawberries. Fruits are amazingly complicated and I think in fact my feeling is that fruits are sort of the model for what cooks do when they're trying to make something delicious. In the background in the recesses of our brains are the example of these natural materials that kind of excite so many of our receptors that we don't need anything else in our mouths and I think cooking is kind of an attempt to create by human ingenuity what plants have been doing for millions of years. Herbs and spices are a different story. So where fruits are combinations of hundreds of different aroma molecules and taste molecules herbs and spices tend to be characterized each one by one or a small number of taste or smell molecules. I've just shown examples here of these very common herbs and spices and the molecules that define them. And it's as I say a completely different situation. Very simple chemistry when it comes to herbs and spices. So why is that? Why do herbs and spices have the flavors they do? Is it for the same reason to attract animals to do some kind of delivery service? The answer is no. And I discovered this for myself the first time when I discovered that herbs and spices can be characterized by essentially one molecule. I went to the chemical supply houses and I ordered Essence of Time, Essence of Oregano and there they are, Time All Carvacral, the flavor impact compounds of those two herbs. What I wasn't expecting when I got them was the message printed on that same label which is that they're toxic. If you see up here harmful by inhalation in contact with skin and if swallowed which is what we're usually doing with Time, swallowing it. Oregano, where's the button here it's not, there we go corrosive causes burns harmful by inhalation in contact with skin and if swallowed. So what's going on there? Why are these things toxic and why do we go ahead and use them? Well, it has to do with the lives of these plants and so if you take for example Mediterranean herbs like Time and Rosemary and Oregano and so on, what you find is that they evolved in a part of the world where they're pretty exposed. This is typical limestone of the Mediterranean area and plants that manage to grow in it and there aren't that many of them are obvious to any goat that happens to be walking by or any slug that happens to be crawling by. In fact slugs have been a very important force in the evolution of our herbs and spices so every time you enjoy something like Time or Oregano or Rosemary you should be thanking the slugs for forcing them to make those chemicals. So what happens is that the plants who live in that kind of environment have to protect themselves otherwise they're just going to be eaten and some of them protect themselves with spines. So there's a plant underneath there and it's grown up above itself this network of thorns that's impossible to penetrate without getting badly scratched. Here's a rosemary plant that's growing out of a hole in the limestone that you can't even see because it's plugged it so completely. There's probably a millimeter of soil in there and it's somehow still managing to grow but it's completely exposed and the way plants that grow in environments like this where they're really threatened by being consumed by hungry animals is that they use chemistry to protect themselves. So these plants make chemical weapons, they're full of them that's what makes them taste the way they taste. Why don't we get sick off of them? Why aren't they toxic to us? Well if you take a rosemary branch and put it in your mouth and chew it like a sheep it'll be toxic to you, right? Your mouth will burn and if you manage to swallow it it's probably going to irritate you all the way down but we don't do that. Instead we use these materials as flavorings. We make our foods more interesting by adding complexity from these compounds and that's why we're not so much bothered by them. It also seems that for many of these compounds these plant defenses end up kind of goosing up our chemical defenses. We're not trying to poison other creatures but we do have to deal with molecules like time all the time in our diet and our bodies have developed ways of detoxifying them and getting rid of them and the more of these we have up to a certain point the better because these induce the enzymes in us that are necessary to do a good job of that detoxification. So up to a certain point it can be actually good to get these things and again that probably reflects our evolution along with them as hunter-gatherers. So fruits, herbs and spices then there are the other kinds of plants that we eat vegetables in particular and the same thing turns out to be true for vegetables. It's kind of obvious in the case of the onion family onion and garlic and so on it's kind of obvious in the case of the cabbage family especially things like Brussels sprouts which can be very bitter. You can tell that the plant is making an effort to discourage you to eat it and part of what's happened in domestication is to lower the levels of those compounds to make them more palatable which may not be a good thing for our health even if it does make them easier to eat. But it's also true of lots of other plants in our environment that make them more as people look around to see what's edible and what have we been ignoring. So evergreen trees for example the pine-iness of pine, the spruci-ness of spruce those come from terpenes that are related to the terpenes in herbs that make that typical evergreen forest smell. Those are defensive compounds. We find them pleasant but the bugs that try to eat the plants don't. Clovers in leucerne all around this site there's clover growing and in that hay smelling there was one bin that was nothing but leucerne I think and those have a very special aroma. The aroma that comes from coumarin which is also found in the tonka bean and which is closely related chemically to vanilla. So if you found it as the sun kind of comes in and out it hits a patch of vegetation out here and you end up with that kind of sweet clover smell that's what it's coming from. It's coumarin. Coumarin is a defensive compound that keeps bacteria and insects in and around the soil from eating those plants. And it turns out that even the most ordinary green leafy vegetables their aromas come from defensive compounds. So it turns out that green leaves have chloroplasts that's what makes them green those little green dots in the cells up there. And within the chloroplasts are molecules related to oils. We don't think of leaves as being high in fat and oil but in fact they do have a significant amount and those fats themselves don't have any aroma those molecules are too big this molecule down here is the kind of fat that you find in the chloroplasts and those molecules are just too big to have any kind of aroma or taste. But if those molecules are broken down into pieces those pieces are small enough that they can give us an aroma sensation. And that's exactly what happens whenever those leaves are broken the cells are damaged enzymes mix up with the chloroplasts the structural molecules are broken down into smaller pieces and that's where the smell of grass comes from. When you cut the grass if you mow the greenery out here and you get that very typical green smell that's coming from hexanal and its relatives these breakdown products. And it turns out that different families of plants have different enzymes that give you different breakdown products when the tissue is damaged. So the cucumber-y aroma of cucumbers comes from little chains that are 9 carbons long instead of 6 in the case of hexanal. And of course if you've ever tasted borage an herb that makes these beautiful blue flowers those flowers smell exact and taste exactly like cucumber and it's because that family also has this enzyme that gives you a 9 carbon fragment instead of a 6. And then mushrooms it turns out the mushroomy smell of mushrooms are all coming from 8 carbon chains of exactly the same kind. They don't have chloroplasts but they have other structures in them that generate these compounds. So the characteristic aromas of many of our vegetables come from these breakdown products and the breakdown products are part of the plant's defensive system. Otherwise why would it be breaking down those molecules? Plants generally don't do things for no good reason. So if you take a plate of sprouts and you spray them with hexanal which is what those sprouts would make if they began to be eaten by insects or if they began to be attacked by moles and then you let them sit around for a few days if you've done the spraying they don't get mold at all but if you don't do the spraying they do. So if you kind of pre-inoculate them with hexanal they're much longer lasting and in fact these breakdown products are now being used commercially as preservatives but natural preservatives because that's what the plant would be doing anyway. And this is kind of a complicated diagram but speaks to much of what Stefano was talking about this morning that the moment an insect begins to bite into a leaf that damage takes place, hexanal is produced and that has an immediate reaction in about a minute or less but in addition to that those same hexanal molecules diffuse into the rest of the leaf and act as a signal to the rest of the leaf to start making more of its defensive compounds before the caterpillar gets there. And beyond even that because the molecules are volatile some of them kind of float off of the leaf into the air where they can reach neighboring leaves on the same plant or neighboring plants and give the same message to those plants. So plants do communicate with each other and they let them know and kind of prime each other to defend themselves against predators that have just arrived on the scene. Now in the case of green herbs like mint you've got both things going on. You've got the essential oils that are the sort of immediate and specialized version of the defense but then if you break into the leaf you're also going to generate hexanal and those elements of the defense. You don't always want to do that and this is a wonderful diagram from a paper a few years ago studying the effects of different ways of handling an herb in order to see what kinds of flavor profiles you can get from exactly the same leaf depending on how you treat it. The leaf is Japanese pepper or asansho which has several different qualities to it but the ones that they were looking at are not the buzzy numbing kind of sensation but the different aromas that you can get from it and there are two different ways that you can handle asansho in Japan one is to grind it up in a mortar or blend it or something like that but the other is to slap it. You put the leaf in your hand and you spank it and then you put it into the dish and bartenders these days do that a lot with mint here to illustrate what it is you're doing. If you're working with something like mint and it has these external external hairs and then you damage the leaf by say putting as you make an ordinary cocktail put the leaf in the bottom of the glass and then muddle it break it up then you're going to get the mint aromas but you're also going to get the green aromas from the destruction of the chloroplasts. Sometimes you don't want that sometimes you want just the mint flavor and not the green flavor partly because the green flavor quickly turns into other things it doesn't stay fresh and green forever it begins to the hexanal molecules react with other things in the plant and you end up with off flavors eventually so if you want just the mint aroma what you can do is handle those mint leaves so that you only break the glands on the outside you can take two leaves for example because most of the glands are on the bottoms of the leaves you can take two leaves put them bottom to bottom and just rub them back and forth very lightly you don't break the leaves themselves but you do break the glands then you drop them in whatever you're making and you're only going to get the mint flavor and not the green flavor what the study of the Japanese pepper showed was that slapping does the same kind of thing if you look at the three different lines here one represents what you get if the leaves are intact the dashed line one of the leaves have been slapped the solid line and if they're crushed the dotted line so here's the intact leaves it's a little bit citrusy it's fresh and green to some extent pleasant kind of generic flavor and a little bit woody and then if you slap them you actually get much more citrus more floral about the same fresh green more pleasant because the other aromas have gone up so you've really accentuated the citrusy quality but then if you crush them you end up with a huge boost in what they call undesirable grassy which I think is just way too much of the fresh green and fresh beginning to turn into stale so depending on how you handle the leaves you can get very different qualities out of them ok shifting now from herbs and spices and what happens when you slap them to things that have to do more with the way plants are grown both in agriculture and in the wild either qualities are different so it turns out that I mentioned the herbs that can have very different profiles growing in close but different places because there may be more slugs over here than there are over there or on the mountain top and the valley it turns out that a single plant can undergo that kind of change when it's growing right next to another one so in a study of the differences between conventionally and organically raised bok choy they found that in conventional agriculture because you're protecting the plants from attack by insects they have a certain level of these defensive compounds of various kinds if you let the insects in of course the leaves look terrible but in fact at least judging by flavor and by defensive compounds they're actually much richer than they would have been in the conventional agriculture more over what they found was that if in organic agriculture the plants are not attacked by insects the plants that are not attacked by insects more resemble the conventionally grown plants than they do the attacked organically grown plants in other words stress by insects is in a way a good thing because it induces more defensive compounds, more flavor compounds, more antioxidants and things like that in the vegetable so as I say that may look terrible and it may look un appetizing and you probably wouldn't want to put a whole leaf of that but it would be a shame to throw it out because there's a lot of good stuff in there a slightly better piece of news about trying to get the best out of produce raised in agriculture is that you can in fact fool plants into thinking that they're being attacked by insects when they're not so you can get the same kind of effect as I just showed you in that previous slide but without the leaf being eaten and it turns out that fungi so disease causing organisms in plants and insects which also attack plants their structures are built out of a material called chitin which is not found in any other animals and it's not found in plants themselves it's also found in crustacean sea creatures because crustaceans and land insects are very closely related so all these things contain the substance in them called chitin for the plant the presence of chitin is a sign that it's about to be attacked by either fungus or an insect and so the moment it detects any sign that there's chitin in the vicinity of that as a signal to start making defensive compounds so it turns out that what you can do is take any of those materials but it's easiest to use crustaceans because there are a lot more of them and their exoskeletons are more substantial grind up those exoskeletons treat them so that some of the chitin is soluble and you get something called chitosan on the soil or on the developing seed or on the growing plant and you end up inducing those same defenses the enrichment of flavor the enrichment of antioxidants without the plant actually being attacked by insects which is a pretty cool effect it's only been known for a few years it really hasn't even begun to be exploited this is not meant to make you think that these plants which have been treated are somehow better than these because they actually don't look that good any of them they've all been grown in a laboratory just to demonstrate that growth is enhanced in the presence of these elicitors and defenses and this is a practical way to make more flavor in vegetables and herbs and then it also turns out that physical stress growing plants in restricted water conditions or in high salt conditions even though it ends up making the plants dwarfed because they don't grow as well the plant that does grow is again much much richer in defensive compounds, flavor, carotenoids the B vitamin A and B vitamins as well the plant feels as though it's under stress it's putting more of its effort into protecting whatever tissues it's able to make so those are a few interesting things and I think useful things to know about the chemistry of flavor in plants again as the speakers have said we're just beginning to understand these amazing creatures and it seems to me that the more we stop and pay attention to them, smell them, chew them, get to know how many there are, the better we'll be able to make use of these amazing partners as far as on this planet. Thanks.