Does "light" really mean light?

In a simple demonstration playing around with light products floating/sinking in water a fascinating contrast emerges.

Try submerging the following two pairs of products: ordinary and light mayonnaise, and diet coke (or other cola vs. cola light).

Light mayonnaise floats lower than ordinary mayonnaise. In the case of the soft drink, cola light floats while ordinary cola sinks! What's going on?



Explanation
The term in question is density:

Mayonnaise
The main ingredients in mayonnaise are water and fat/oil:
Ordinary mayo: 80% fat, 16% water
Light mayo: 40% fat, 50% water

Fat floats in water. A larger proportion of fat makes the mixture closer to pure fat and vice versa.


Cola
Cola can be considered as water with some dissolved material. Ordinary cola is, as such, a sugar solution with a few other additives (taste, aroma, colour etc.).

Cola light contains the artificial sweeteners Sucralose and Acesulfame K. Both are far sweeter than table sugar, sucrose (650 times and 180-200 times, respectively, ref. Belitz). Thus, far less sweetener is needed. If we assume that all other ingredients are the same, then far less material is dissolved in the light version. The same total volume with less material --> lower density. Thus: pure cola light would float up in ordinary cola taken that they didn't mix.


In both the mayo and cola cases, there is some air (or trapped gas) inside the tube/can. This makes the tube/can float higher than in the case of the pure mayo/cola. However, as long as the volumes are the same, this doesn't make any difference. If it wasn't for the air, both cans would in fact sink, and the experiment wouldn't be.


A question of using and understanding scientific concepts
The concepts relevant to this is not only "light", but also (amongst others) "(chemical/dietary) energy" and "density". If something floats, we usually say that it's "lighter than water". However, two kilograms of wood is heavier than one kilogram of water, but it still floats. To me as an adult, it's probably easy to grasp, but placing this in an educational context makes it important to use the correct terms. So, "cola has higher density than cola light" would be more correct.

It's quite easy to put this to the test: measure both the volume and weight of a can/bottle of cola and compare. The one that sinks (highest density) weighs the most taken the same volume. Another version of this experiment is concealing the labels, letting the students know the content without telling which is which. The task is then to use knowledge and reasoning to deduce which is which.

Using the term "diet" rather than "light" would of course make the whole case less diffuse, but then a fascinating aspect in the experiment and following discussion is lost. This is the reason for using "light" instead of "diet" in the first hand. However, this may be a nice way of introducing the energy concept of (chemical) energy, kcal and kJ, and contrast this against "light" used in different contexts.


Natural sciences are evidently not only concerned with nature itself, but just as much the language describing nature.

Erik


Refs.:
- Belitz et al., Food Chemistry 3rd ed., Springer 2004
- A Swedish version of the cola experiment at SkolKemi pages of University of Umeå

Do we need to know about dispersions: addition

Slightly embarrassing, I forgot to include Hervé This' work on dispersions.

Hervé This has done some beautiful systematic work on dispersions which he has termed "Modelling dishes". He has several publications on this, but one of these is a paper in British Journal of Nutrition: "Modelling dishes and exploring culinary ‘precisions’: the two issues of molecular gastronomy". It's (at the moment, at least) free for download through IngentaConnect.

Although probably not suitable for the everyday school teacher (but who knows), this is great stuff for those with a more-than-average interest in science vs cooking.

Erik


Post addition, February '09: the Swedish book "Den tekniske kocken" (The Technological Chef") uses in a very consistent manner the different dispersion terms, and show graphically what sorts of dispersions are important in various foods and dishes (although the book recieved a harsh review, "worst cookbook of the year", in Matälskaren).


Reference: This, H., Brit. J. Nutr. 2005, 93, S139.

Do we need to know about dispersions?

Most of the matter and materials that surround us aren't pure compounds or true, homogeneous solutions. If we want to give a science education that is relevant and connected to everyday life, why then is so much of the labwork we do focussed on pure substances and solutions? ...and will the home-/professional cook benefit from knowing a little about dispersions?

A look in the kitchen cupboard and fridge revealed, apart from water and air, the following pure compounds and true homogeneous solutions: sugar, salt, natron (sodium bicarbonate), some of the soft drinks, and some refined vegetable oils. All the other stuff is dispersions, i.e. more or less stable mixtures of compounds/phases that don't mix.

Dispersions and colloids
A related word is colloids, but to my knowledge the word dispersions has lately been adopted as a collective term for colloids, aerosols, foams and emulsions. A dispersion is a homogeneous mixture of two or more phases that are immiscible (won't mix). What is mixed are solids, liquids and gases. The table below gives an overview. In fact, it's quite an enlightening exercise to have a look around and try categorizing the stuff around you. Bread is a foam; cheese, most vegetables and meat are gels; milk, butter and mayonnaise are emusions, just to mention a few.


Click picture for full size version in new window. Click here for Norwegian version


Why dispersions?
In Norwegian school science books and science teacher training literature, matter is divided only into pure compounds and mixtures, see below. The problem with this is that students (and teachers) don't get a language to deal with the stuff that surrounds them. To most of us, foam is a known phenomenon, and emulsions are also known to some. However, these are secondary terms rather than the primary term dispersion.

Conclusion
The term dispersion is not mentioned in the Norwegian curriculum for primary,secondary and high school (Kunnskapsløftet, eng.: "The Knowledge Promotion"). Do I think the term dispersion should have been included in the curriculum? Maybe, maybe not. This new curriculum isn't meant to give detailed instructions to what should be taught, but to what competences the students should have inherited after a certain level. It's up to the school/teacher to fill he subjects with a content as long as the students achieve these competences.

So, if we want the kids to experience a science education related to their everyday life, rather than stuff they'll meet only in science lab, maybe we should start talking about (and playing with) dispersions.

Also, for those of us who would like to benefit from scientific knowledge when we cook, this may afford a good way of viewing ingredients and foods (i.e. previous entries on Tomato foam and Egg white foam).

Erik

Post comment:
Addition to this post in the following post "Do we need to know about dispersions: addition"

Five cardinal rules in cooking

Inspired by Martin's blog entry "Ten tips for practical molecular gastronomy", I came to remember Östen Dahlgren's five cardinal rules in cooking:

1. Be critical of recipes
2. Stop and think - should I really do [it like] this?
3. Keep in mind how the heat is distributed/transferred
4. Keep in mind what is soluble in what
5. Taste while you're cooking - often
   

(my translation)

Dahlgren has written the book "Laga mat - Hur man gör og varför" ("Cooking - How to do it and why"), which is a Swedish counterpart to McGee's "On food and Cooking".
Dahlgren's list is a simpler version of the ten rules that Martin lists up. Although less comprehensive, the short list is easier to keep in mind whenever you're cooking, and I think that's a virtue. I could have commented further on each point, but I think I'll keep it short this time.

What is soluble in what? Blueberry juice in chili oil
(Photo: Erlend Krumsvik)

Furthermore it seems to me that the various tips in Martin's list demand quite different degrees of knowledge and experience. "Learn how to control the texture of food" and "Learn how to control taste and flavor" demand quite a lot of either knowledge or experience (or both) from the cook. On the other hand, "Know what temperature you’re cooking at" doesn't demand much more than the skill of using a thermometer. Of course, Dahlgren's list also operates on different levels, but maybe less so than Martin's. Or is it maybe me seeing things a little too much through my own eyes here, being more accustomed to Dahlgren's rules knowing them for a longer time?

One of my personal favourites is by the way Martin's 9. tip, being imperative in science and science education: "Keep a written record of what you do! ".

Maybe should we go for a happy marriage, making one complete list for the Molecular Gastronomy enthusiasts and a shorter one for everyone else? A future post, either here or at Martin's blog, should certainly have two such differentiated lists. A joint venture?

Erik

A kindred spirit

My first experience with the annual ASE (The Association for Science Education) conference was at The University of Birmingham 3.-6. January. A paradox was that I had to go all the way to England to find that one of the most interesting experiences was to be a Swedish lecturer.

A packed programme with hoards of parallel sessions, spanning most thinkable and unthinkable science education issues; from the highly inspiring/enthusing to the one that give you the feeling "I never thought it was possible to completely ruin something so inherently fascinating". However, one experience left all of the other sessions in the shadows: Hans Persson at the Swedish National Centre for Education in Physics (and The Stockholm Institute of Education) had two sessions: "Creativity in the Science Classroom" and "Curious About Science?". His approach to science teaching was so fresh, vital and inspiring that the session ended in the audience giving standing ovations (the first time I've experienced such after a conference lecture).

What makes this special? First of all, the strong focus on students' interest/attitudes towards science in addition to the knowledge. Interest before knowledge, maybe. If you don't enjoy dealing with science, you won't learn much. Other key factors are having courage to be truly playful and enthusiastic, and utilising every aspect of everyday life to impart science. I also share his quite strong criticism of the kind of science teaching that is separated from everyday life, i.e. lab equipment which its sole purpose is for use in science education, but which doesn't exist anywhere else (note that this primarily applies to primary and secondary school, college/university level may be quite a different ballgame).

The other thing that makes this stand out is that he managed to convince me that he's got a firm foundation for this approach, possibly both theoretical/ideological and empiric, both from primary/secondary school and teacher training. His book on concept building is sure to find it's way to my bedside table soon (only in Swedish, unfortunately, but he's published books in English as well).

Anyway, I don't think I've seen such a fresh approach to science education during my five years in the game, and I decided to post this although strictly it doesn't deal with food and science education (although he touched in on that as well).

A visit at his web page, which bears the subtitle "How can we awaken interest in science and then keep that interest alive?", gives a small glimpse of his thoughts and work. I find this so important that I've put the link in the permanent links list in the right hand margin.

Erik

Link: www.hanper.se (both English and Swedish, but the Swedish pages are somewhat more comprehensive).

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

Erik

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.

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)

Erik

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

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.

Erik

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

Erik

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).

Erik