Friday, August 12, 2011

Notes: A Soupçon of Science: Creativity at the interface of chemistry and cuisine

Although I will be going down to Wellington for the tail end of their annual food festival Wellington on a Plate, I was sorely disappointed that I would miss out on the lecture by Professor Kent Kirschenbaum of New York University titled A Plate of Molecules: Chemical Gastronomy.  Quite apart from the fact that I am only spending a weekend in the capital, and the lecture is on a Wednesday, the tickets for the talk sold out months ago.  So, it was like all my Christmasses had come at once when I discovered only a few days ago that he would also be presenting in Auckland.  Unfortunately, there was so little advertising of the lecture, brought to us by the New Zealand Institute of Chemistry as part of the celebrations for the International Year of Chemistry 2011, that the room was less than half full!

No matter, for those of you that didn't manage to make it for whatever reason, I hereby give you my version of events.

A Dessert Topping and a Floor Wax?

Professor Kirschenbaum started off by playing a video of the New Shimmer commercial, a 1976 parody aired on Saturday Night Live.  You can watch it here (from 02:49).  In the skit, the same product is used both as a floor wax and a dessert topping.  Is this possible?

Basically, we are looking for a substance which is an edible soap.  Soap is an amphiphile, with both water-loving and fat-loving properties. It turns out there is a class of chemical compounds, called saponins, which suits our purposes exactly.  Saponins are phytochemicals, which means they can be extracted from plants.  In fact, the word "saponin" is derived from a plant called soapwort, a.k.a "Bouncing Bet".

The two major commercial sources of saponins are Quillaja saponaria (soapbark tree) and Yucca schidigera (another desert plant), but saponins can also be found in everyday food items, as you can see from the foam when you soak chickpes, for instance.  They are often added to drinks such as root beer to give them a foamy "head". 

Here is the saponin content of some selected plant materials (from Saponins: Properties, Applications and Processing, Critical Reviews in Food Science and Nutrition, Volume 47, Issue 3, 2007):
SourceSaponin content (%)Reference
Soybean0.22–0.47Fenwick et al., 1991
Chickpea0.23Fenwick et al., 1991
Green pea0.18–4.2Price et al., 1987
Quillaja bark9–10San Martin and Briones, 1999
Yucca10Oleszek et al., 2001
Fenugreek4–6Sauvaire et al., 2000
Alfalfa0.14–1.71Fenwick et al., 1991
Licorice root22.2–32.3Fenwick et al., 1991
American ginseng (P. quinquefolium L).
Young leaves1.42–2.64Li et al., 1996
Mature leaves4.14–5.58Li et al., 1996
Roots (4 year old)2.44–3.88Li et al., 1996
Oat0.1–0.13Price et al., 1987
Horse chest nut3–6Price et al., 1987
Sugar beet leaves5.8Price et al., 1987
Quinoa0.14–2.3Fenwick et al., 1991

Professor Kirschenbaum proceeded to attempt to make his own "New Shimmer' using the following recipe:
    3mL Quillaja saponaria extract
    70mL water
    5mL lemon juice
When he whisked these things together in a bowl, it began to turn into foam.  This could be used as a mild cleanser or shampoo, as he demonstrated by smearing the bubbles onto his shirt and through his hair.

He then added a bit of sugar to make the foam more palatable, and gave it to an enthusiastic young volunteer from the room to sample.  Only then did he mention the bitter aftertaste.  The child pulled a face.

Actually, the idea of making a foamy dessert using a saponin is not new.  In Aleppo in the Middle East, they make a white, fluffy, meringue-like dip called natef, commonly eaten with a semolina cookie called karabij, using something commonly translated as soapwort root.

(As an aside, did you know that licorice is made from the root of Glycyrrhiza glabra? It contains glycyrrhizic acid which is 50 times sweeter than sugar.)

Can something further be done with the foam?  For instance, a NZ company called Angel Food sells a product called  Vegan Meringue Cookie Mix.  Could we also make an eggless meringue?  The answer is yes, though the result is not quite the same as a real meringue, and one of Professor Kirschenbaum's assistants in New York spent ages piping the foam and baking it for us to try. (Not sure how the speaker managed to bring so many over, but we ate some after the lecture and the "meringue" bites did indeed have a bitter aftertaste.  You also have to keep them dry as the ones I tried to take away melted into my hand.)  Professor Kirschenbaum was going to try to bake a pavlova with the foam in Wellington, but thought he was going to fail, because pavlova has a complex texture, crunchy on the outside and soft on the inside (can anyone in Wellington let us know how that went?).

The Quillaja saponaria eggless meringue had a bitter aftertaste and drew moisture from my hand
 Liquid Smoke

natural.  Look at the popularity of the Slow Food Movement and the numbers of the farm-to-table advocates.  Just because something is natural, however, does not mean it is good for you.

Take smoke for instance.  We like the flavour of smoked fish, meats, and cheeses, so what is actually in smoke?  Molecules such as guaiacol, camphor and eugenol help provide an attractive flavour profile, but smoke also contains anthracene, pyrene and benzo(a)pyrene, which are not only 100% natural, but 100% carcinogenic.

If you live in an apartment, you wouldn't be able to use a smoker anyway.  You could, however, add a smoky flavour to your food using something called liquid smoke, a substance produced from passing smoke through water.  The flavour could then be concentrated using a rotovap, which speeds up evaporation by reducing the pressure, thus lowering the boiling point of water.  Although the safety of using liquid smoke as a food flavouring is still being assessed, it does seem as though it would be better for you than actual smoke, since some of the larger insoluble components that are bad for you would drop out as tar.


If you've been at all interested in the science of food, you will have heard of a cooking technique called sous-vide, which involves holding food in vacuum-sealed bags at a lower temperature for long periods of time.  This is to ensure that the food cooks evenly, rather than having the outsides done long before the insides come up to temperature.  It also means there is no chance of overcooking.  Eggs cooked at 63 degrees C for an hour will still be soft with a slow-running yolk, for instance.

The French Culinary Institute blog has some pretty amazing pictures of various foods cooked at different temperatures, such as this one of salmon, which interestingly has two temperatures resulting in goodness.  Cook between these temperatures, however, and the fish will squeak when you chew it.

One of the amazing pictures and diagrams from
Mango Caviar

The application of science can turn food into a delightful and magical experience.  One of the dishes produced in El Bulli, the most famous and widely respected restaurant in the world at the forefront of molecular gastronomy (unfortunately now closed), is their mango caviar.

Mango caviar from El Bulli restaurant, courtesy of
To make this, you mix mango juice and sodium alginate and put it into a dropper.  Then you squeeze out little pearls into a calcium chloride bath.  The calcium ions form a cross linked gel with the alginate ions in what is known as polymer ion exchange, and you end up with a liquid surrounded by a thin jelly coating.

Making mango caviar
Ferran Adrià of El Bulli has also used the same technique to make spherified pea soup, which apparently "explodes in your mouth like ravioli".  Cute.

Stretchy Icecream

The concept of stretchy icecream wasn't invented by a mad scientist.  Salep dondurma has been made in Turkey for 300 years already, and is believed to have originated in the southeastern part of the country.  Made from milk, salep (a flour made from the tubers of the wild purple orchids of the Orchis species) and mastic (a resin from the mastic tree, Pistacia lentiscus), the icecream is denser, more elastic and slower to melt than Western icecream.  In some places, it is eaten with knife and fork, and it has a "pillowy", marshmallow flavour.

Turkish icecream sellers even make a whole show around the properties of their product:

Here is a recipe for maraş dondurması, a variety which has more salep than usual:
    3 Tbsp salep
    5 cups milk
    1 cup sugar
    1 small piece mastic, ground
    other flavour ingredients, e.g. pistachio

"Salep" comes from the Arabic for "fox testicle", and can refer to the orchid as well as the flour made from it, which is also used to make a popular Turkish beverage.  It contains glucommannans, chain molecules which contribute to the unique texture of Turkish icecream.
Salep increases viscosity
As for mastic, it is a tree resin or sap which has been used in food for over 2000 years.  It may even have been found in an ancient shipwreck in the seabed of the Mediterranean.  Only in 1998 was this resin identified as Cis-1,4-poly-β-myrcene, and it is one of the original chewing gums.  Not too sure whether it is added to dondurma just for its flavour, or whether there is also a functional component.  (Professor Kirschenbaum was planning to investigate Kauri gum in New Zealand, as the resin from the Agathis australis tree has also been used as chewing gum in the past.)

A tin containing pieces of mastic, and a box of salep flour

It is now forbidden to export salep, as the purple orchids it comes from is not a sustainable ingredient.  Fortunately, it is possible to make stretchy icecream using a similar ingredient instead.  The konjac plant, from the tubers of which shiritaki noodles are made, is also high in glucommannans.  A number of people have now tried making "konjac dondurma", and it seems to be pretty successful, by all accounts.  Professor Kirschenbaum's recipe went something like this:
    2g mastic (Chios Gum Mastic, Large Tears)
    8g konjac flour
    dry ice
    1.6L milk
    400g sugar
Cool with liquid nitrogen.

Experimental Cuisine Collective

Professor Kirchenbaum is a founder of the Experimental Cuisine Collective, along with pastry chef and former dessert restaurant owner Will Goldfarb, and Amy Bentley of the Department of Nutrition, Food Studies and Public Health at New York University.  The group was founded in 2007 and now has over 1,800 members.  Its mission is to advance delicious cuisine while educating students in the natural sciences.

One inspiring young person Professor Kirschenbaum mentioned is Lauren Hodge, the winner of the inaugural Google Science Fair 2011 in the 13-14 year old age group.  She studied the effect of marinades on the amount of carcinogens produced by barbecuing chicken and discovered that having a more acidic marinade component (lemon juice) inhibited the production of a carcinogenic compound, while soy sauce actually increased it.

Suggestions for Chemists and Chefs:
Be creative

Recommended reading:
Harold McGee, On Food and Cooking
Jeff Potter, Cooking for Geeks
Hervé This, Molecular Gastronomy
Myhrvold et al., Modernist Cuisine

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