Learn the science behind:
No matter where you look, there’s a good chance you’ll find some surprising science hidden in a seemingly not sciency dish. That is definitely the case for these kurma, which we lovingly call “Trini kurma” since the recipe comes from Trinidad & Tobago. It’s a fried cookie, coated in ginger sugar syrup. Apart from it being delicious (once you start eating them, it’s hard to stop) they are a perfect demonstration of the crystallization science of sugar and the layering of fats in dough!
What is “Trini kurma”
Trini kurma comes from Trinidad & Tobago. There’s a good chance you will find these ginger-spiced cookies on special occasions such as Diwali, religious ceremonies or festivities in general. Nowadays you can also find them in supermarkets and smaller stores outside of these occasiosn, they’re a great treat.
The kurma consists of two main components: a deep-fried cookie and a sugar coating on the outside. The cookie itself isn’t sweet and doesn’t contain any sugar, but does contain a mix of spices. All the sweetness instead comes from the outer sugar layer. It’s a layer of crystallized sugar that’s been boiled down with ginger for an amazing overall flavor. The combination of the coating and cookie is what makes this snack work so well and they each have their peculiarities in making them!
Kurma cookie science
As you can see in the photo above, kurma cookies are long narrow cookies, a little wider than they are thick (though that does depend on the cookie, some make them wider than others). If you bite in the cookie you will notice a very important characteristic: its layered texture. Thanks to the layers of dough and air the cookie is crunchy, without being too hard to bite through!
You create this flaky cookie texture by creating pockets of fat through the cookie dough. Once you heat the cookie, the fat will melt and seep into the rest of the cookie, leaving behind a pocket. The fat has prevented the different dough layers from touching each other on forehand, and once they’re cooked they will remain separated. The process is actually very similar to that of short crust pastry.
Creating these fat pockets isn’t that hard. All you need is a fat that is solid at room temperature, but that will melt during frying. Examples of this can be butter, ghee, shortening or even coconut fat. Start by rubbing the fat (see for recipe the bottom of the post) into flour. By just mixing the butter and fat by hand, you will create little pockets of fat throughout the flour. Aim to only have small pieces of fat left, barely visible to the eye. The fat is ideally well surrounded by flour so it doesn’t just seep out completely during cooking.
Why fry kurma?
Kurma cookies aren’t baked in the oven, instead, they are deep-fried in oil. It’s another reason why they’re narrow and long. This makes them a great shape to fry. Once the cookie is surrounded by the hot oil the heat travels through in a matter of minutes, cooking the cookie quickly.
While cooking the cookies expand slightly, their thickness roughly doubles whereas the length and width remain pretty much the same. That expansion happens because of the evaporation of moisture and the melting of the fat in the cookie. The evaporated moisture pushes onto the dough to expand and the melting of the fat helps create those air pocket that expand.
You could also bake the kurma in the oven. However, that will take a lot longer. The so-called heat capacity of hot oil is a lot higher than that of hot air in the oven. That is, it contains more ‘energy’. It is why frying can cook and heat food a lot fast than an oven would (oven-baked chicken also takes considerably longer than a fried version, as is the case for oven-baked potatoes vs. french fries). The shorter, more intense cooking of the kurma makes them turn brown faster and improves the expansion of the cookie.
We did try oven baking kurma (see photo below). However, even after 20 minutes in the oven at 180C they were still pale in color, even though the were cooked through. Also, they clearly hadn’t expanded as much. As such, don’t skimp on the deep frying!
Tips for frying kurma
When you’re deep frying kurma, or any other food for that matter (especially french fries) you’re trying to achieve two things:
- Fully cooking the inside: you don’t want any raw dough left in the center. Even though these cookies are thin, it takes a while for them to fully cook through.
- Brown the outside: the final cookies should be a nice light brown, but not burnt. This browning happens faster and faster at higher temperatures.
In order to achieve this balance you want to fry them at a constant, moderate temperature. In our case 160-180C (325-350F) works very well. Of course, thinner cookies cook through faster so can handle higher temperatures. The opposite is true for very thick cookies, they need longer to cook, so you’d better use a temperature on the lower end of that scale to prevent them from burning before being cooked through.
Once the cookies come out of the fryer they will be super crispy and crunchy. The heat has not just achieved those two goals above but it also evaporates moisture, which makes them even crunchier! These cookies stay crispy for really long, as long as they are protected from humidity (best to pack them in an airtight container).
Ginger sugar coating science
The cookies are great, however, what really makes these cookies shine is the ginger sugar layer on the outside. The ginger and sugar lift the cookie to a whole other level. They make it almost impossible to resist eating more.
Super saturated sugar syrup
As you can see in the photos above, the sugar on the cookies is hard and crystallized, it has even turned white. In order to achieve this effect, you’ll be making a supersaturated sugar solution, that you pour over these cookies. This may sound more complicated than it is.
Sugar dissolves in water. As you have probably seen in several instances (e.g. adding sugar to tea or coffee) more sugar is able to dissolve in water if it is warmer. If you’ve made caramel before, you’ve used this as well. When you put a pot of water + sugar on a stove and bring it to the boil, you will notice that more and more sugar dissolves as it heats up.
Once a sugar syrup is boiling, you are starting to evaporate moisture. As a result, you’re concentrating the sugar solution even more. The ratio of sugar : water increases when more water evaporates. You have now dissolved more sugar in water than would have been possible at room temperature. If you would cool this syrup back to room temperature it will be supersaturated, that is, more sugar is dissolved than is technically stable at that temperature. The slightest disturbance will now cause the sugar to crystallizes, thus not being dissolved in water anymore! (Phase diagrams help explain this science in even more detail!)
This is exactly what you’re doing when making the kurma syrup. You make a supersaturated sugar solution. By then pouring it over the cookies and stirring it through you’re cooling the syrup and forcing the sugar to recrystallize again. While you’re stirring the syrup through your cookies you will notice that it is first very sticky. However, once it starts crystallizing and properly cooling it will be more crunchy than sticky.
In order for this effect to happen, you have to concentrate the sugar solution just enough, but not so much that there isn’t enough liquid anymore to help the syrup spread over the cookie. Expert kurma makers can judge that they have reached this stage by looking at the consistency of the sugar syrup. They are looking for the “thread stage“. However, if you’re not (yet) as much of an expert, a thermometer is your best friend here. You’re looking for a temperature of about 112-114°C (233-237°F).
Fixing kurma sugar syrup
Keep in mind, whenever you’re making sugar solutions like these, it’s hard to really mess them up! If you’ve heated the syrup a few degrees too hot, chances are it will still work for these cookies. However, if you want to be sure, you can always add some more water. This will reduce the sugar concentration, reduce the boiling point and you can just heat it again to the correct temperature.
If it seems your sugar syrup just doesn’t want to crystallize even though you’ve cooked it well, you can help it along. Just add a little bit of icing sugar (a teaspoon for the recipe below is already enough). By adding icing sugar you’re adding sugar crystals. These sugar crystals will serve as growth sites for sugar to crystallize from the syrup, speeding up crystallization.
What about the ginger?
Trini kurma wouldn’t be kurma if it weren’t for the ginger in the sugar layer. Apart from some spices in the cookie, most of the flavor of kurma comes from the sugar coating. When making kurma the ginger is actually cooked with the sugar syrup. This is done on purpose. For one thing it helps the flavor of ginger to disperse throughout the sugar syrup. But, it also helps create the right type of ginger flavor.
One of the major flavor molecules in ginger is gingerol. It is what makes fresh ginger slightly pungent. By cooking the ginger this molecule gets converted into zingerone. This molecule is less pungent and as such works a lot better with a sweet snack like kurma!
Now bring all that science together, by actually making kurma :-). Enjoy!
Jehan Can Cook, Mithai: How to make Guyanese mithai, Oct-14, 2019; It seems to be that Guayana has a very similar snack! However, there it’s called mithai. Flavors and preparation methods are very similar though!
Crosby, Guy, Cook’s Science, 2016, Chapter 30: Ginger