Skip to 0 minutes and 19 seconds chemist here at the University of Reading. I founded and set up the flavour centre, which is also housed here at the University of Reading, in the Department of Food and Nutritional Sciences. What we do particularly up here is look at aroma, and aroma is what you detect in the nose. It’s what you smell. And the difficult thing about measuring aroma is the fact that, in any food, 99.99999% of it is not aroma. So we only want that tiny bit that is aroma. We analyse in a sort of vial that looks a bit like this. And we’ve got the food in the bottom, but what we actually analyse is what’s at the top, in the space in the top.
Skip to 1 minute and 7 seconds So that’s what you smell if you smell a cup of coffee or a cup of cocoa. So we stick a fibre in there that will absorb the aroma compounds onto it. And then we take that over to our instruments, which will separate out the aroma compounds, and then we can identify them and we can also smell them if we need to as well, because in many cases, the human nose is more sensitive than the instruments that we have. My name is Christopher Hew and I’m a final year student at the University of Reading. And I’m taking Food Science BSc as my degree course.
Skip to 1 minute and 40 seconds The work that I’m doing in the flavour lab involves in analysing the aromatic compounds found within chocolate, from the modern day today, as compared to the ones that are from 300 years ago during the Georgian era. The sample that we have here is from the recipe made in the Georgian era, and this is chocolate from the modern day today.
Skip to 2 minutes and 6 seconds This sample here is from the Georgian era and it has more of a fruity and rosy aroma, while this one from the modern age has less of the fruity aroma and it has a more roasted taste as well. In the bulk production of chocolate today in modern industries, the roasting temperature is usually higher and longer, which gives rise to more of pyrazines as compared to the esters that we get in the sample from the Georgian era. This is probably because of the fermentation period that is taken when making the chocolate cake from the Georgian recipe.
Skip to 2 minutes and 53 seconds So what I’ve got here is a sample of the Georgian chocolate that Chris made earlier. What I’m going to do is put it in this instrument and the robot will do all the rest. But what’s going to happen is that it will pick it up and place it in the incubator where we’re going to extract all the aroma compounds. It’ll then inject the aroma into the instrument and this part of instrument is going to identify what’s what.
Skip to 3 minutes and 33 seconds Here we got 59. So what it’s doing now is just incubating the sample. It’s set at 60 degrees, which is about the temperature that we’d be drinking it at. So the fibre’s now waggling around, and it’ll do that for about 30 minutes, to give all the compounds in the chocolate a chance to actually absorb onto the fibre. And then, after 30 minutes, it will inject it into the injection port, because what we’ve got inside here is a 30 metre coil, and all the compounds go round at a different rate, depending on how heavy they are and how volatile they are. So that’s how the separation takes place. And at the end of the column, they go through the mass spec.
Skip to 4 minutes and 25 seconds And the mass spec bombards them and creates a fingerprint, which allows us to determine which compounds have come out when. What we’ve got here is a trace from the Georgian chocolate. And each of these peaks is a compound from the chocolate, and each peak potentially has an aroma. So if we look at some of them, you’ll see that we get a different fingerprint on the bottom. And this fingerprint tells us what’s what. And if we look at that one, for example, that’s a particularly rosy note. So when Christopher was talking about smelling rose, this will be the note that he’ll have been picking up.
Skip to 5 minutes and 5 seconds Further along, if you look at that peak and perhaps that peak, we know what they are, and they’re the ones that give a particularly toasty, roasty note to the cocoa. These are present in the Georgian sample, but they’re higher in the modern day sample. There are lots of other peaks there. These ones for example, there’s a whole group of peaks here and these are all esters. So these are the ones that are giving the fruity notes to the Historic Royal Palace’s chocolate, to the Georgian chocolate. So they’ll smell fruity, strawberry, banana. When combined with all the others, they give you that impression of cocoa.
Comparing chocolate flavour intensity
In the previous Step 3.11 you joined Christopher to find out how traditional ‘cakes’ of chocolate were made from pure chocolate nibs, in the King’s Chocolate Kitchens at Hampton Court Palace.
How do the aromatics in a sample of drinking chocolate made from one of these Georgian ‘cakes’ compare to a sample made from a contemporary cocoa powder? Are the differences in the intensity of the aroma reflected in the flavour intensity of each drink?
Watch this video to find out more as Dr Jane Parker, Director of the Flavour Centre at the University of Reading, analyses and compares the two samples prepared by Christopher in the lab.
Why not try conducting a flavour intensity experiment in the comfort of your own kitchen? Jane mentions that the human nose is extremely sensitive to aromas - this experiment provides an ideal opportunity to put this to the test! Can you smell the difference in aroma intensity between samples of drinking chocolate prepared using different liquids? Is any difference in aroma reflected in any difference in flavour intensity? Why not prepare samples of drinking chocolate, using the same amount of liquid and teaspoons of cocoa, then compare the aroma and the flavour of each.
You will need some basic ingredients; your preferred brand of powdered cocoa and two or more liquids to mix with the powdered cocoa to make a hot drink. You may like to try mixing cocoa with water, milk (any variety such as full fat, skimmed, lactose-free, soya or almond) or alcohol such as wine or port. You won’t need any special equipment; just the cooking utensils you have readily to hand in your kitchen.
Which method of making hot chocolate releases the strongest aroma and richest chocolate flavour? Cocoa powder mixed with water or milk? If you’ve tried mixing it with alcohol, was the flavour intensity any different?
Share your findings in comments area below.
The University of Reading has a long established research interest in chocolate. It is home to the International Cocoa Quarantine Centre (ICQC), the only facility of its type in the world. The University of Reading took over responsibility for cocoa quarantine from the Royal Botanic Gardens at Kew in 1985 and operates to ensure that cocoa breeding can be satisfied without transferring pests and diseases from one cocoa growing region to another. You can find out about the work of the International Quarantine Centre on their website.
© University of Reading and Historic Royal Palaces.