4 Feb 2007

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.


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.

3 Feb 2007

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.

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).


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