Potato density vs Age (expiration date of potatoes 1^st March 2011)

As discussed we have been measuring the density change of the potato over a number of days. The potato was left out at room temperature and the density measurements were carried out using the same method as before (filling measuring jug with water to assess volume/mass change).

The density change has been fairly minimal, and the precision of the scale (accurate to 1 gram) has perhaps hindered the experiment somewhat. Having said that there is clearly a negative correlation between density and age.

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New density measurements and Calibration

As advised from the last meeting we placed the measuring jug on an electronic scale, reset the scale to zero and filled it with 400g worth of water. We found that there was a small error in the jug which produced the systematic errors in our previous measurements. We marked the real 400ml mark with a pen and took new volume and weight measurements. I also skinned two of the potatoes to check the removal of skin didn’t significantly change the density (The rows highlighted in the same colour correspond to the same potato). Below is a table of results of potatoes with the skin on:

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As part of his MSci project Karim Bahsoon has been investigating the effects of varying blanching time on the properties of french fries. Jason Chang, who works with Karim, is involved in measuring surface starch content and crunchiness of the ready chips.

Potatoes were cut into fries and placed in boiling water for times varying from 0-12 minutes. These were then submerged in vegetable oil at 170C for 4 minutes and then fried again at a higher temperature of 190C for a further 2 minutes. The second fry is thought to help with crust formation and adds to the crunchiness of the fries.

By measuring the density of the fries before and after the cooking process, we found that the density ratio of the fries decreased with increasing blanching time. We also saw thicker crust formation and sustained crunchiness of fries blanched for longer. Unfortunately prolonged blanching times also meant the fries were fragile and almost falling apart before frying, so care had to be taken when handling these.

Density ratio vs. blanching time of french fries

We plan to test alternative methods such as introducing a drying stage to the process as well as looking at the transportation of starch during blanching to get a better understanding of how to make the perfect french fries.

Dr József Baranyi visited Imperial College to discuss the predictive food pathogenic models Sergey Goryunov and Vedish Bhatoolaul are developing. Sergey is looking at developing new methods in Population Level Modelling (PLM) and Vedish is working on an Individual Based Model (IBM).

Imperial College FoodCycle is organising a charity dinner cooked by Tom Aikens. It will be held on the 21 March 2011 at Whole Foods Market, High Street Kensington. FoodCycle is an organisation that uses raw food ingredients donated by various supermarkets and other suppliers, that would otherwise be wasted, to cook meals for people who cannot afford a hot meal. An excellent example to follow!

As a part of the MSci project on Cooking a Steak, we would like to communicate the physics and those physical processes that take place during cooking to the general public. Karim Bahsoon and Jason Chang are the two fourth year undergraduate students working on this project.

The dessert course of the menu will be a chocolate mousse by Tom Aikens. Tom is a Visiting Researcher at the Physics Department and he has been advising us on the menu. In addition to his help Tom actually cooked all the courses for us so that we know how the original versions taste.

So this Monday I was at the Tom Aikens restaurant where Tom showed me the secrets to his amazing chocolate mousse. The main ingredients are italian meringue, a milk chocolate creme anglaise and whipped cream. The easiest way to make the creme anglaise is in the Thermomix which provides a well controlled cooking environment with exact temperatures that can be set. Too many spoilt custards even in professional kitchens justify the use of this wonderful machine. In this picture Tom is using his Thermomix for making creme anglaise:

Creme anglaise in the making with Thermomix

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Yesterday we submitted our first paper on food research to Journal of Food Engineering entitled “Tenderising effect of sodium bicarbonate on pork loin”. The paper is based on the work Xiao Liu Chu has done on comparing the effect of sodium bicarbonate with sodium chloride solution (brine). The authors are XL Chu, P. Török, C. Paterson, Tom Aikens. Here is the abstract of the paper:

“We investigated the effect of a 3% concentration solution of sodium bicarbonate (treatment A) and pure sodium bicarbonate (treatment B) on pork loin samples. These were compared to a 5% salt brine (treatment C), controls consisting of tap water (treatment D), and untreated samples (treatment E). The effect of the treatments was investigated by measuring weight change at 30-minute intervals during marinating (treatment A and C), the changes in cooking loss after heating at 60˚C (treatment A – C) and the relative mechanical load (N) (treatment A and C).

Pork loin samples under treatment A experienced a (50 ± 14) % higher increase in weight after 390 minutes of marinating as compared to treatment D. This suggests an increase in water holding capacity. The result of heating pork samples subjected to treatments A and B showed a significantly smaller cooking loss than the controls, losing (39 ± 7) % and (33 ± 10) % less in weight, respectively. This implies that sodium bicarbonate caused the meat to better retain water. The mechanical testing showed that meat fibers from treatment A required a smaller force to cut compared to treatment D. Altogether, our study shows that sodium bicarbonate causes a change to the texture and the water content of meat.”

I have visited Dr József Baranyi, leader of the Computational Microbiology Research Group at BBSRC’s Institute of Food Research to discuss possible collaboration on predictive microbiology. We have strong interests in developing reliable ways of constructing models for non-isothermal predictive microbiology. Currently population level modelling is based on first order kinetics for both growth and inactivation. This model however, is only applicable on a very limited and constant temperature range. Both professional and home cooking, on the other hand, take raw food ingredients through rather complicated heat cycles which in turn violate the validity conditions of the model. We have two fourth year undergraduate students, Sergey Goryunov and Vedish Bhatoolaul, working on this project.

This blog will keep a record of our research that we carry out at the Physics Department of Imperial College relating to food. The projects include heat diffusion modelling in meat products, understanding of the physics of different cooking processes, and predictive microbiology. More entries will follow shortly.