Gulab Jamuns and Crystal Structures

Recently we had a Garden Party for the Cambridge University India Society (CUIS), and as in any event that sees mass participation, where one either falls short or has more food arranged for than required, this one had quite a few things left over, and the committee members were given one or more food items as token rewards (and mine was rightly so, given my liking for Gulab Jamuns!).

Wikipedia gives the following description of Gulab Jamuns:

Gulab jamun is a milk-solids-based dessert, popular in countries of South Asia such as India, Sri Lanka, Nepal, Pakistan and Bangladesh. It is also common in Mauritius and the Caribbean countries of Trinidad and Tobago, Guyana, Suriname and Jamaica. In Nepal, it is widely known as lal mohan, served with or without yogurt. It is made mainly from milk solids, traditionally from freshly curdled milk. In India, milk solids are prepared by heating milk over a low flame for a long time until most of the water content has evaporated. These milk solids, known as khoya in India and Pakistan, are kneaded into a dough, sometimes with a pinch of flour, and then shaped into small balls and deep-fried at a low temperature of about 148 °C. The balls are then soaked in a light sugary syrup flavored with green cardamom and rose water, kewra or saffron. These days, gulab jamun mix is also commercially available. Gulab jamun is often served at weddings and birthday parties.

It is one of my favorite sweets, besides rasmalais and rasgullas. So, in this case, the Gulab Jamun was put in a jar filled upto about a quarter with the syrup. And it was in this setting (the sweets in the syrup) that I found a rather interesting and simple demonstration of cell structures. Hexagonal Closed-Packed (HCP) crystal structure, to be precise.


In crystallography, a fraction of volume in a crystal structure is occupied by constituent particles. These structures can be of various types: Hexagonal close-packed, Face-centered cubic, Body-centered cubic, Simple cubic and Diamond cubic.



It is often tough to understand subtle nuances of these structures, initially as a student of crystallography. For one, HCP did create some problems about how consecutive layers pack and fall into place and how that affects the crystal structure in its entirety.

A possible solution: Gulab Jamuns (in syrup)!

The Gulab Jamuns float in the syrup, and given sufficient amount of syrup, the Gulab Jamuns come together in a circular formation. Given the right size and number of Gulab Jamuns, HCP layers can be reproduced. Once the uppermost layer is in place, the rest of the Gulab Jamuns get into place underneath, and so on. Now, one can use a stick or thin ladle to get through the holes in the first layer and manipulate the subsequent layers. If the second layer falls exactly underneath the first and so on, one has a particular formation. One can also have a formation where the Gulab Jamuns in the second layer fall in the holes of the first layer, and so on. One can then remove the Gulab Jamun and measure it’s diameter.

Also, the jar has measurements put (it so happened that this one did), and so the entire crystal structure can be measured precisely (a little more ingenuity can help in measuring diagonal measurements and on-top measurements; maybe reference strings of finite length).

A simple application of Gulab Jamuns kept in syrup that I found interesting and devised while having a few (being so fond of them!).


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