Today’s molecule – furan

I don’t need ANY bad news about my espresso coffee!

From FECYT – Spanish Foundation for Science and Technology, via “Eurekalert

Here is their press release…

“Coffee in capsules contains more furan than the rest”

Coffee in capsules contains more furan than the rest, although the levels are still within safe health limits.

“Preparing a coffee in a drip coffee maker is not the same as making one in an espresso machine or from capsules, because these give rise to differing levels of furan”, Javier Santos, a professor at the Department of Analytical Chemistry at the University of Barcelona and lead author of the study, tells SINC.  Concern has risen over recent years about the presence of this compound in foods, because of its toxic and carcinogenic effects in animals, as well as the fact that the International Agency for Research on Cancer has listed it as a possible carcinogen in humans.

“The results, published online in the Journal Food Chemistry, reveal that higher concentrations are found in espresso (43‐146 nanograms/mililitre) than in coffee made in drip coffee makers, both in the case of normal coffee (20‐78 ng/ml) and decaffeinated coffee (14‐65 ng/ml).  The levels of these toxic products were “slightly lower” (12‐35 ng/ml) in instant coffee, but a great deal higher in those made from the capsules of a well-known brand, which showed up higher levels (117‐244 ng/ml).”

“The reason for these higher levels is due to the fact that hermetically-sealed capsules prevent furan, which is highly volatile, from being released, while the coffee makers used to brew this coffee use hot water at higher pressures, which leads to the compound being extracted into the drink”, says Javier Santos. The longer that coffee is exposed to the air in cups or jugs, meanwhile, the more the furan evaporates. ”

“Different values, but not dangerous: The researcher stresses that, in all these cases, the levels of the substances found are within the limits considered to be “safe” to health. In fact, the team has estimated the amount of furan ingested as a result of coffee consumption in Barcelona, obtaining values of 0.03‐0.38 micrograms/kilogram of body weight, which is less than the maximum acceptable level (2 μg/Kg of body weight). In order for furan ingestion to exceed the maximum acceptable values, a person would have to drink at least 20 cups of capsule coffee or 30 espressos per day (for the brands with the highest furan content), or 200 instant coffees. These estimates were made on the basis of 40 ml cups and an average body weight for coffee drinkers of around 70 Kg.”

“The study also shows that furan concentrations are lower if coffee is roasted at low temperatures over a longer time (140ºC for 20 minutes) than in coffee roasted under usual conditions (200‐220ºC for 10-15 mins).”

Furan, like acrylamide, is one of a group of carcinogenic substances that can form when foods and drinks are subject to heat treatment. They are the result of a reaction, known as the Maillard reaction, between carbohydrates, unsaturated fatty acids and ascorbic acids or its derivatives.”


M.S. Altaki, F.J. Santos and M.T. Galceran. “Occurrence of furan in coffee from Spanish market: contribution of brewing and roasting”. Food Chemistry 126 (4) 1527, June 2011 (Available online December 2010). Doi: 10.1016/j.foodchem.2010.11.134.

A winter of food chemistry instruction

Can’t show the students for administrative reasons, but we had a good and educational time once again.

Bringing you highlights from the second iteration of  “BRINGING FOOD CHEMISTRY TO LIFE”.



Mayonnaise and egg white foams, and ways of messing them up that were instructive for the chemistry lesson.


Using the Brookfield viscometer to show how viscosity changes with molecular weight @ equivalent w/w concentration, and how it changes with w/w concentration @ equivalent molecular weight. The Brookfield with the helipath stand was also good for demonstrating how the viscosity of the mayonnaise decreased with increasing shear rate [shear thinning]. The helipath stand makes sure the sensor is going through an as yet unsheared region, taking time-dependent thixotropic behaviors largely out of play.

Fun with spherification whilst experiencing the gel forming capabilities of biopolymers with different gelling mechanisms [alginates, glucomannans, methylcellulose].

COFFEE WEEK: browning reactions, & foam and emulsion production and stability in espresso as related to roast degree [and therefore  the interplay between arabinogalactan peptide, and maybe galactomannan, extractability [during hot water extraction] and thermal degradation [during roasting] in determining the stability of the espresso crema]

Prepared for a cupping [monsooned, versus washed arabicas, versus robusta]

Color versus roast degree via tri-stimulus color meter.

How fun to have an espresso machine as part of the lab equipment! And coffee roasters too.

The instructor/barista hard at “work”

STARCH WEEK: not just formal viscometric studies, but also hands on experience of the different gelatinization temperatures and pasting behaviors of a variety of starches [e.g. potato versus wheat].

The instructor/starchista hard at work.

Using freshly made noodles as a way of bringing to life the profound  functional influence of differences in starch amylose content on food texture.

MEAT WEEK: As a plant scientist I find this work really hard to clean up because of all the fats!

Water holding capacity, gelation with salt and heat, transglutaminase, effect of pH and nitrites on color


Pretzel logic

Final lab session of our Food Chemistry class this year.

20100311 AR pretzel ANNOT

An experience of the effects of pH on browning reactions.

We make a variant of traditional soft pretzels, using a rather leaner formula than often used [for us no milk or eggs]. The loss of lactose from the milk and glucose from the egg might have contributed to our failure to get the same level of color development we saw last year when we used a full rich formula with egg and milk.

20090312 pretzels

Still it is a great way to experience the effect of pH shift on the color and aroma generated by primarily Maillard browning, allthough at pH 14 in the 4% NaOH, other reactions are very likely.

2010 formulation


2009 formulation

untitled 2009

A poolish is a 50:50 mixture of flour and water BY WEIGHT with about 0.1% of the flour weight as dried [instant] yeast [NO SALT] that is allowed to ferment around 16 hours before being added to the final dough.

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

Beating the teapot effect

(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.

Hopefully some food chemistry came to life…

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.


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

Pretzel lab

Coffee day

Starch again

Meat lab

Baking lab