» Maillard Bringing food chemistry to life

October 29, 2009

Teapots, fluid dynamics, and baked potatoes – but what are we to do with the buttery taste?

Filed under: Baking, Uncategorized, barley, food chemistry — rossand @ 12:56 pm
Tags: Baking, barley, food chemistry, Maillard, physics

Beating the teapot effect

Authors: C. Duez, C. Ybert, C. Clanet, L. Bocquet

(Submitted on 17 Oct 2009)

Cyrill Duez’s team show that superhydrophobic surfaces stop the tea from wetting the inner surface of the spout and pretty much stop the dripping.

Richard Alleyne, science correspondent for the UK Telegraph newspaper, says this backs up the old adage that putting butter inside the spout stops the drip.

But no-one is saying what we should do with the buttery taste – maybe get used to it like the Tibetans have with tsampa (toasted barley flour, green tea, and yak butter) – see picture on the last page of the linked PDF file

Of course all this leads to some interesting side trips on the internet, this time to the web page of Lydéric Bocquet an the Liquids @ interfaces’ group at the Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Lyon 1, and a link to a paper of his from The American Journal of Physics from 2007 called “Tasting edge effects“. The paper backs a hypothesis that, to quote him, “the baking of potato wedges constitutes a crunchy example of edge effects” . He goes on to say in the abstract- “A simple model of the diffusive transport of water vapor around the potato wedges shows that the water vapor flux diverges at the sharp edges… This increased evaporation at the edges leads to the crispy taste of these parts of the potatoes“.

All I can say is, thank goodness this happens and that baked potatoes have extra tasty edges, all a function of increased drying rates that speed Maillard browning.

FotoosVanRobin via Flickr

Coffee stains explained

And an hour later – even more interesting things – like the paper 12 years ago in “Nature” that explained the nature [pardon the unintentional but awful pun] of the rings in coffee stains via a flow from the interior of the liquid to the exterior, bringing suspended material with the flow and depositing it at the edge of the drying droplet. And coffee is a good example because oft he amount of dispersed but not dissolved material in the cup. It would be interesting to see if the effect is more pronounced with espresso than drip filter given the far higher level of suspended solids in an espresso cup.

“Capillary flow as the cause of ring stains from dried liquid drops“ Robert D. Deegan et al

Nature 389, 827-829 (23 October 1997) | doi:10.1038/39827 – even folks without a full text subscription should be able to access the abstract via this link .

Who’da thought Nature would be interested in coffee stains – still, the journos and editors, they probably live on coffee.

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March 15, 2009

Hopefully some food chemistry came to life…

Filed under: Uncategorized — rossand @ 11:21 am
Tags: bread, Coffee, espresso, foams, food chemistry, genetics, Instruction, Maillard, polymer science, rheology, viscosity

There are many elements needed to create a good and compelling class – good material, a willing instructor, but the essential element is enthusiastic and dedicated students. It is a circular argument: enthusiastic students generate enthusiasm in the instructor, which generates enthusiasm in the students, and around we go again.

I was privileged to have an almost uniquely good natured, good humored, and hard-working group who were willing to participate in this experiment in teaching food chemistry. Of course not everything that was tried worked flawlessly – but no good thing was ever perfect the first time around. And we were not having enough fun…

The key structural element of the class that I believe led to our moderate success was the use of case studies to highlight many of the basic elements of food chemistry. The two more successful ones were bread making and espresso.

Breadmaking was viewed as a system both in narrow and broad senses. In the narrow sense: a matrix of interacting components in the dough and in the finished product. In the broader sense; as the progress of a variable agricultural raw material through its intermediate processing steps (e.g. milling) through to final processing, storage, and consumption.

In the narrow sense we were able to incorporate elements of…

Polymer Science (entanglements, glassy and rubbery states and their responses to changing temperature and plasticization [water])

Rheology (viscoelasticity)

Starch behavior (gelatinization, susceptibility to attack by amylases, & retrogradation [junction zone nucleation and growth] and staling)

Maillard reactions (the effects of water activity, temperature, pH [mostly with the pretzel lab], and the contribution of fermentable reducing sugars from damaged starch)

Foams and foam stability (dough gas cells as a solid/liquid foam stabilized by proteins and lipid-based surface active components, the foam to sponge transition from dough to bread)

Enzymatic activity and thermostability (mostly amylases: the increasing susceptibility to hydrolysis of undamaged and damaged starch granules and finally gelatinized starch; the different windows of opportunity for extensive hydrolysis of gelatinized starch during baking by fungal, cereal, and bacterial amylases )

In the broad sense we were able to observe elements of…

Genetics (the interaction with genetically determined kernel hardness and subsequent starch damage during milling, fermentable sugar production by amylases, and Maillard development of crust color; the genetics of gluten protein variability and its effects on gluten and dough viscoelasticity),

Rheology/Polymer science (fracture mechanics of kernels, polymer entaglements – stress build up and subsequent relaxations as vital steps in the transformation of flour, water, salt, and leavening [yeast or sourdough] to bread)

Espresso was also viewed in these two ways.

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In the narrow sense we were able to incorporate elements of…

Rheology - the contribution of particulates to viscosity, the contribution of polymer size to viscosity and to the persistence of espresso crema as expressed by changes in foam drainage related to viscosity

Maillard (of course) - during roasting, the delay while the beans dry out, the increasing darkness, the formation of aromatic volatiles, the production of carbon dioxide, and the role of carbon dioxide in the formation of the cream foam.

Microstructures and inhomogeneity – the idea of espresso as a polyphasic colloidal system (e.g. Piazza, L; Gigli, J; Bulbarello, A (2008). Interfacial rheology study of espresso coffee foam structure and properties. Journal of Food Engineering 84 (3) 420-429. )

In the broad sense we were able to incorporate elements of…

The idea of coffee as an agricultural product; variability in composition related to species, region of growth, the fact that it needs intermediate processing before it can be roasted (allowing an opportunity to explore cell wall polysaccharides in detail – particularly the pectin in the cherry mucilage).
Of course there was much more – but this is just a summary.

And of course student engagement is vital. The following pictures tell the story, and I need to express tremendous thanks the class for their collective contribution to a successful term !!!

Starch lab