The Science of Ghee & How It’s Made

After kneading the chapati dough, rolling it into circles and baking it on our tawa, we never skip one essential last step. Adding a thin layer of ghee on top. Whereas the ghee is hard when it comes from the fridge, it melts away as soon as the ghee touches the hot chapati.

The chapatis are then devoured while dipping them into a delicious portion of butter chicken (of course, containing ghee) or some palak paneer. Ghee coated chapati does wonders in lifting any dish up and eats great just as is, well after all the other sauces and dishes have disappeared.

Ghee is an core ingredient of Indian cooking. It is used to add fat and flavour to a whole range of dishes. Its role is somewhat similar to that of butter in French cuisine and is essential to get that flavour balance just right. Butter and ghee aren’t even that different at all, both start out as cow’s milk. So where does ghee deviate into its own unique process and uses?

What is ghee?

Cows play a very important role in the Indian Hindu society and as a result, so do the dairy products that can be made from their milk. Ghee is just one of many products made from the milk of a cow and also plays an important role in various religious ceremonies.

Milk is made up of mostly water as well as some proteins and fat. Most milk contains less than 5% fat and that happens to be the one component you’re after when making ghee. Ghee consists of >99% milk fat with just a little bit of water and a few other minor components. Since milk only contains quite a small amount of fat, which is fully dispersed throughout, the main challenge of making ghee is trying to separate out as much of the fat as possible. Ghee manufacturing really just is a separation process.

Milk fat

Milk fat, or ghee, is made up of a mixture of different fats, each called a triglyceride. Each of these triglycerides contains a central backbone (called glycerol) with three fatty acids attached to it. The properties of these fatty acids impact the behaviour of the fatty acids and triglycerides as a whole. The two most common fatty acids in milk fat are myristic acid and oleic acid, but there are several others as well as is shown below.

When milk is transformed into ghee, nothing happens to these fatty acids. Ghee is made up of the same fatty acids as the fat in milk is at the start. As mentioned earlier, ghee manufacturing is all about getting these fats separated from the rest of the milk.

Science of splitting fat from milk

When making ghee you need to get rid of both the moisture and the majority of the proteins in the milk. Since most of the proteins (not all) dissolve very well in water, generally those two can be taken care of simultaneously to a large extent.

You can use three different scientific principles to split fat from water: density differences, churning or boiling off moisture.

Separation using density differences

If you’ve ever made chocolate milk at home using cocoa powder and milk, you will have noticed the cocoa powder sinking down if you leave it too long without stirring. This is caused by a density difference between the powder and the milk which can be described using rules around sedimentation.

A similar effect happens in milk. The density of fat is lower than that of water. As a result, water will sink down to the bottom whereas the fat will rise to the top. Gravity by itself can accomplish this. You can speed it up by using centrifugation. This effect is barely non-existent in store bought milk because the fat droplets in that milk have been homogenized. The droplets are so small that they won’t sink or rise fast enough for you to notice over shelf life. In fresh milk though, this can happen within a matter of days (at room temperature).

Churning

Another way to separate the fat from milk is to help the separate fat particles to clump together. Once they’ve formed a clump of fat large enough for us to see and touch we can sieve it out, for instance by using a cheese cloth. This method is called churning. It is almost always combined with the previous one.

Cooking off moisture

Water evaporates when it is heated up warm enough. If you leave a pot of water to boil on the stove without a lid, the level will go down over time. Fat on the other hand does not evaporate. It might break down or catch fire, but it won’t evaporate like water does. As such, if you boil milk carefully for an extended period of time, theoretically, you will end up with just fats and proteins.

Boiling off moisture is very energy intensive. As such, it is never used by itself by it is often a crucial step towards the end of ghee manufacturing when a lot of the water has already been removed using one of the other methods.

Ghee manufacturing

Using these same principles there are roughly two ways to make ghee. All methods start by getting rid of the first large quantity of water by transforming milk into cream. Cream has a fat content just below 50%. Centrifugation, so using a difference in densities, is the most common large scale method for this. Once you end up with cream, the two methods can differ.

Method 1: Cream → Butter → Ghee

Once you have your cream, it can be made into butter using the churning process. During churning all the fat globules will clump together. By keeping the butter cool (below its melting point) the fats will all remain solid in these clumps. As such, it is possible to drain of the rest of the moisture. By kneading the butter for a while even more moisture can be pushed out. This process brings the moisture level down to about 20%, still way too high for ghee.

Next, the butter is melted down and brought to the boil, just under 100°C. The butter is now warm enough for the moisture to evaporate over time. The butter is kept at this temperature for an extended period of time until most of the moisture has evaporated. The exact time will depend on the volume that’s being heated and the efficiency of the process.

As long as their is still a few percent of moisture in the butter, the temperature can be kept constant quite easily. It takes a lot of energy to evaporate water, so the majority of the heat goes into enabling evaporation. However, once the moisture content gets very low, the temperature of the ghee can easily raise above 100°C. Some manufacturers prefer to go up to 120°C to develop some darker more caramelized flavours whereas others keep the ghee at slightly lower temperatures to have less of such flavour development.

In all processes used, the final ghee will contain less than 1% of water.

Method 2: Cream → Ghee

Instead of turning milk into butter first, you can also convert cream into ghee immediately. Before cooking, the cream is washed a few times to get rid of non-fat solids such as proteins and is then also heated to slowly evaporate the moisture. Generally speaking, this method requires more energy since evaporating water is very energy intensive.

Ghee variations

Within these two different types of manufacturing and few variations can be made to either improve the flavour or further optimize the process.

Fermentation of the cream

Ghee can be made from freshly made cream immediately. However, it is also possible to take some more time and leave the cream to ferment (as is done for cultured butter). This fermentation process is quite similar to the process used to make yogurt for instance. By adding bacteria (often lactic acid bacteria) the cream will turn slightly sour. The bacteria convert all the remaining sugars in the cream into acids. Along the way they produce a lot of other flavour molecules.

After fermenting, which can take anywhere from half (twelve hours) to a full day. The exact conditions will depend on the cream, temperature and the types of bacteria used, among other factors.

Fermentation impacts the flavour of the ghee (which some do and other don’t find desirable) and it tends to extend shelf life. Also, because the cream will have thickened somewhat, it makes churning and separation of the water slightly easier.

Gentler cooking

If you’re using the first method, so converting butter into ghee for making ghee, you can change your cooking procedure at the end. Instead of cooking at temperatures around 90 ° C, heat butter to 80-85°C.

An interesting phenomenon, called stratification will occur at these temperatures. Instead of it rolling and boiling, the butter will separate into three separate layers. The top layer contains some proteins. The middle layer is mostly fat and the bottom layer contains about 80% of all the moisture from the butter. By splitting the bottom layer from the rest of the butter you get rid of a large part of the moisture while using very little energy.

You finish off the ghee by cooking the other two layers at the slightly higher temperatures to get rid of the remainder of the water.

Shelf life of ghee

Butter has a limited shelf life when stored at room temperature (20°C). There still is quite some moisture in butter and as a result, it will oxidize quite easily, resulting in unappealing smells. This might have been fine for a farmer living in a temperate Dutch climate some some hundred years ago.

However, this isn’t good enough if you live in a warm climate, such as that in large parts of India. The butter will be almost continuously molten and won’t be stable at all. Since ghee does not contain any moisture, it is far more stable under these conditions and can be kept for a longer period of time.

Why is ghee stored at room temperature?

Because of its extremely low moisture content, ghee doesn’t spoil because of micro organisms. The low moisture content also slows down (but does not fully prevent) most other chemical reactions which may result in off notes caused by rancidity. As a result, as long as the ghee is stored air tight (oxygen in the air causes oxidation) it can be stored at room temperature for several months.

Once the ghee has been opened and the air tight seal has broken, it will oxidize. In this case storing it cooler or in the refrigerator extends its shelf life.

Luckily, it will still be soft enough in the fridge to dip in your spoon and get a chunk for ghee for your freshly baked chapati. Which should taste even better, now that you know how the ghee has been made.

References

Dairy Technology, Methods of manufacture of ghee, 2014, link

Palanivel Ganesan, Butter, cream and ghee products, 2013, In book: Milk and Dairy Products in Human Nutrition: Production, Composition and Health, John Wiley & Sons Ltd., p.412-434 link

Bhavbhuti M. Mehta, Butter, Butter Oil and Ghee, 2009, Gourmet and Health-Promoting Specialty Oils

Priyaski, J., How to Manufacture Ghee: Process, Methods, Packaging and Storage, link

Pure Indian Foods, Difference between ghee and cultured ghee, 2017, link

Tasmanian Butter Co., Cultured butter, link

YouTube, How to make pure ghee in village style? Jul-14, 2018,, link