27 Dec 2006

Christmas dinner trimmings - a hot potato? (part two)

Many a Christmas dinner, we end up with the potatoes falling apart in the dish and pale olive-green Brussel sprouts. Does it have to be like this? Using a little scientific knowledge in the kitchen can help.

Part two - green vegetables
Brussels sprouts and the broccoli: Do you prefer a fresh, vivid green colour, or a dull olive green? The colour in green vegetables is due to chlorophyll, which is a compound well suited to play around with. The green colour in chlorophyll is due to a magnesium atom (in fact, an ion) attached to a porphyrin ring, and acid can substitute this magnesium altering the colour. Try adding a little lemon juice or vinegar to the water next time you cook green vegetables if you want to do a “sabotage experiment” just to see what you may want to avoid. This kind of sabotage experiments are, in my opinion, just as important as the “successful” ones.

Chlorophyll molecular structure at pH = 7 (neutral/basic) to the left, and pH<7

Fruit and vegetables contain a little acid, so if we use pure water or steam the, this acid is in fact sufficient to alter the colour in a negative way. As a remedy, try adding a couple of teaspoons of (sodium) bicarbonate/natron per litre of water. This makes the water slightly basic. The water will turn green as well, but there is more than enough chlorophyl left for the vegetables. Short cooking times is also recommended, as chemical reactions take time, and the replacement of magnesium is no exception. This is probably the reason that the colour change is more visible in Brussels sprouts than broccoli, the sprouts cook longer and thus more of the chlorophyll is degraded.

Left: cooked with a little bicarbonate (pH ca. 9), right with a little lemon juice or vinegar (pH ca. 4.5)

So, in the two posts conclusion: treat the potatoes and vegetables the opposite way.

Happy New Year


Background info:
McGee, H. (2004): McGee on Food and Cooking – An Encyclopedia of Kitchen Science, History and Culture. London: Hodder and Stoughton.
Belitz, Grosch og Schieberle (2004): Food Chemistry (3. utg.). Berlin: Springer.

PS: have any idea why the water turns green on adding bicarbonate? Please let me know.

18 Dec 2006

Christmas dinner trimmings - a hot potato? (part one)

Many a Christmas dinner, we end up with the potatoes falling apart in the dish and pale olive-green Brussel sprouts. Does it have to be like this? Using a little scientific knowledge in the kitchen can help.

Part one - potatoes
In Norway, Christmas dinner is often accompanied, amongst several things, by boiled potatoes and Brussels sprouts. The potatoes are often of a mealy sort, and peeled before cooking rather than after.

Mashed potatoes are a result of the outer parts of the potato being cooked too much before the inner parts are tender. Potatoes contain pectin, the cement which holds the cells together. Pectin is soluble in hot water, and when mealy potatoes are boiled, the pectin dissolves in the water. The cement is gone, and the potato fall apart in it’s separate cells. There is, however, an enzyme in the potato that helps the pectin molecules to cross-link internally, so the pectin stays in the potato. This enzyme is active between 50 and 60 °C. The solution is: leave the potatoes in water at this temperature for 20-30 minutes before heating further up, and your potatoes will not fall apart (use a standard cooking thermometer). But beware; the cooking time will be longer. Cooking bacalhau a couple of weeks ago, I had a fascinating experience (in Norway it goes by the name bacalao. Bacalhau is a Portuguese/Brazilian fish dish, in this case a hot pot with tomatoes, potatoes, onion, clipfish, black olives and olive oil). The potatoes were pre-cooked as described above, peeled and cut in large pieces, and added to the hot pot. After 75 minutes simmering, the potatoes were still not tender, and the guests had to wait another 15 minutes. One and a half hour’s simmering before the potatoes were tender! The potatoes, by the way, kept their shape perfectly even when the dish was reheated.
If you deliberately want the potatoes to fall apart, i.e. to thicken soup, you should do the exact opposite: put the pre-peeled potatoes directly in boiling water.

One problem with such pre-cooking is the off-colour (enzymatic browning). This can be fixed by adding a little acid, a tea spoon of vinegar or some lemon juice, or an antioxidant; a C-vitamin tablet or a tea spoon of pure ascorbic acid does the trick. The acid retards the reaction, while the ascorbic acid (C-vitamin) sacrifices itself in the reaction.

A drawback is that vitamin-degrading enzymes are also efficient at temperatures between 50 and 60 °C, so focusing on texture results in lower vitamin content. For everyday dinner I’d put unpeeled potatoes directly in boiling water to deactivate the vitamin-degrading enzymes, alas deactivating the pectin reinforcing ones as well.

Part two will deal with the Brussel sprouts - how to achieve a fresh green colour rather than a pale olive-green colour. A Norwegian version of this post can be found at www.naturfag.no/mat.

Merry Christmas(-dinner)


Background info:
McGee, H. (2004): McGee on Food and Cooking – An Encyclopedia of Kitchen Science, History and Culture. London: Hodder and Stoughton.

22 Nov 2006

New paper by Hervé This!

Hervé This, co-founder of the term Molecular gastronomy, has published another paper: "Food for tomorrow? How the scientific discipline of molecular gastronomy could change the way we eat
" (EMBO reports, see free html or pdf versions). I've had a brief look, and there are lots of interesting and important issues to be discussed further. He discusses the role of molecular gastronomy in everyday life (and education, although briefly), and confronts the fact that a scientific view on food still has a long way to go if we want to reach people's everyday cooking, and not the high-end restaurants only.

Highly recommended, and I'll give some education-related comments on this in near future.


25 Sept 2006

New curriculum in Norwegian schools (Kunnskapsløftet): Food in science and science in food

(See the posting from 20. June for the discussion on this).

Since June the curriculum (goes also by the name/abbreviations "Kunnskapsløftet", LK06, L06 or R06) has been revised. Now, the final version (at least for primary school) is published (http://www.utdanningsdirektoratet.no/lk06 http://www.udir.no/Lareplaner/Grep). Therefore I've redone the informal food-in-science and science-in-food analyses:

- Food in science - 58 out of 140 subjects may be treated with food as a starting point
Science in home economics - 18 out of 40 subjects may be treated with science as a starting point

This analysis is, of course, a consequence of my personal views of the two subjects. Hence, there may be connections I haven't seen. Also, some of the connections I've made may be far fetched in other's eyes.

Best wishes


20 Aug 2006

Book review: Kitchen Chemistry

It was with immense anticipation i opened the book "Kitchen chemistry" from RS*C (the British Royal Society of Chemistry) when I received it almost a year ago. The book is a collaboration between Ted Lister and the Michelin-star chef Heston Blumenthal known for his Molecular gastronomy-approach to cooking. Upon closing the book after the first read, I must admit I was slightly disappointed (although there are a number of bright spots as well).
Among the things I find attractive is the beautiful layout and extensive digital material following the book, both on CD and on web, including video clips and dynamic Chime molecular structures). Also, RS*C has been very generous in leaving much of the web based resource material for free.

Molecular gastronomy (MG) has afforded a new and very refreshing approach to cooking, bringing science into the home and restaurant kitchen in a wonderful way. The reason for my disappointment is that this book's approach to using science in the classroom (or school kitchen/lab) is, in my opinion, not refreshing in the same sense. This may be exemplified by:

* The table of contents of the book tells us that out of 17 chapters, five are dedicated to salt and its role in cooking. I find this rather lopsided in terms of spending valuable book space trying to catch children's attention to science and food. To me, the sixth chapter "Should beans be cooked with the lid on or off?" also provides an example of what may be interesting to a chef (or an adult), but of limited interest to the children it is claimed to be focused toward: ages 5-11. Is this maybe a result of a chef picking subjects that are the most interesting to him, rather than searching for what may trigger young people? What about taking the French approach of Hervé This and colleagues playing around with egg white foam ("Wind crystals"), an experiment I find fascinating, and which has been successful also in a few Norwegian schools? (see "Egg white foam" posting below)

* Second, the experiments laid out are rather closed ended in the terms that approach, method and result are all given in beforehand. There is little for exploration and imagination for neither teacher nor student if one is to follow the book all the way through using all the resources given on a subject (ppt-files, video and student sheets). Through lack of freedom and open ended experiments, the teacher is in a way relegated. The book seem more directed towards the kind of teacher that would use the resources slavishly, rather than one who would go on experimenting together with the students. Accordingly, teachers wanting to adapt the material to her/his situation and class (rather than following the procedures slavishly) may find that the material has to be revised and readapted to her/his setting, although this seems not to be the intention of the book.

Despite being rather critical, I find a number of fascinating subjects making the book fun to read. Subjects like "The chemistry of flavour" and "The science of ice cream" make my curiosity tick. Furthermore, many home cooks may find it interesting to read about "Why do pans stick?", which by the way R. Wolke has discussed in his book "What Einstein told his cook" posing the wonderful question "Why doesn't anything stick to nonstick cookware? And if nonstick coating won't stick to anything, how do they get it to stick to the pans?". Kitchen Chemistry may be the starting point of fun experiments in the school kitchen, but again - by the teacher that is able to adapt the material to her/his own class and situation rather than following a common path laid out for all.

Maybe the reason for MG being so refreshing, while this book being less, is that MG approaches science on the premises of food/cooking, while this book falls into the traditional pit trap of treating food on the premises of science? For us that are already hooked on science this is a fascinating book with beautiful extra material, but for teachers and students who have not yet fallen in love with the universe of natural sciences, I fear that this may not make it all the way.

Kitchen Chemistry (£19.95) may be obtained from the RS*C Kitchen chemistry web pages (see link above).


14 Jun 2006

Recent food-ucation-related podcasts

Lately, there have been (at least) three interesting podcasts related to science and food:

In Norwegian:
"NRK Verdt å vite spesial" 22. May 2006 - about salt.
Salt is definately a fascinating theme crossing several subjects, both within the sciences and across to other subjects (food, history, social sciences etc.). This programme represents just this interdiciplinary approach.

Erik Fooladi on "Superstreng" no. 34 with Eirik Newth on Kanal 24.
I'm talking about food/kitchen in science education and molecular gastronomy with Eirik Newth on his weekly popular science radio programme. The mp3-file may be downloaded directly from the web site.

In English:
Hervé This in "The Leonard Lopate show" on WNYC New York Public Radio
"Host Leonard Lopate lets you in on the best conversations with writers, actors, ex-presidents, dancers, scientists, comedians, historians, grammarians, curators, filmmakers, and do-it-yourself experts". The French molecular gastronomist Hervé This is co-founder of the research field of molecular gastronomy, no doubt one of the big names in the field. The mp3-file may be downloaded directly from the web site.

Happy listening


12 May 2006

"Opposite-boiled eggs" - Cooking an egg with soft white and firm yolk

Cooking an egg we usually use boiling water, and we need to monitor the temperature carefully. One minute too much, and we get a less-than-perfect-boiled egg. Reason: the interior of the egg (aka: the proteins in both white and yolk) coagulates/stiffens at far lower temperatures than 100 °C. According to Harold McGee the "[...]egg white begins to thicken at 63 °C and becomes a tender solid when it reaches 65 degrees". Furthermore, "The yolk proteins begin to thicken at 65 °C and set at 70 °C [...]". (McGee, pp 85)

So, my thought was: Since it's the temperature that counts rather than the time, I can keep the temperature at 64-65 °C, and the egg will be perfect (to my taste) no matter how long they are cooked: a fool proof method to eggs with tender solid white and soft yolk! The pictures show eggs cooked ad 65 and 68 °C for 6 and 26.5 hours, respectively.

Hervé This also writes about this: "[...]at 62 °C one of the proteins in the white (ovotransferrin) is cooked, but the yolk remains liquid because the proteins that coagulate first in this part of the egg require a temperature of 68 °C. Obviously this would mean longer cooking times, but the result is a perfectly cooked egg" (This, pp. 31)

The proof is in the pudding, so I tried cooking an egg at 65 °C exactly for an hour or more, and was to put it mildly surprised. The egg came out with a runny white but firm yolk!! These come out the same whether they're kept for half an hour (to ensure the same temperature throughout the egg) or 26 °C hours. Another proof, provided the temperature is right, for that the time doesn’t matter in coagulating proteins.

There may be several reasons for this, but one is found in McGee (pp 85): "[…]the major [egg white] protein, ovalbumin, doesn't coagulate until about 80 °C".

So, it seems, this time chemistry played me a trick. We will still have to rely on physics: the reason that we can have eggs with firm white and soft yolk is, when using a temperature well above the coagulation temperature, that the white is "overheated" before the temperature of the yolk passes the point where the yolk stiffens.

There is, by the way, a mathematic model/equation for this. Have a look at Martin Lersch's web site on Kitchen chemistry for a nice diagram and explanation of this.

Happy cooking


References and links:
Harold McGee: On Food and Cooking
Hervé This: Molecular gastronomy - Exploring the science of flavor
Martin Lersch's page "Molecular gastronomy and the science of cooking"

Post-comment (feb. 2009):
Douglas Balwin's excellent "A Practical Guide to Sous Vide Cooking" has a section on sous vide cooking eggs

23 Mar 2006

New teacher's resource: egg white foam

New teacher's resource (Norwegian only) published on Norwegian Centre for Science in Education pages www.naturfag.no:

Å fange luft med egg - Om trollkrem, skum og proteiner
("Catching Air With Eggs - Concerning Troll's Cream, Foam and Proteins")

How much foam can you get from one egg white? Why is it so difficult to get good whipped egg white foam if a small amount of grease, soap or egg yolk is present? Playing with tasts on troll's cream (troll's cream is a traditional Norwegian dessert made of egg whites whipped with sugar and lingonberries - a light and tasteful foam).


Inspiration: Pierre Gagnaire and Hervé This (Wind Crystals)

Addition 6. Feb 2007: Gagnaire's pages are now in French only, see
Cristaux de vent.

Addition 2. Jul 2011: Finnish LUMA centre has posted Troll cream on it's experiment pages.