Friday, October 22, 2010

All You Need to Know about Cooking Oils

Are you sure you are using the correct cooking oils or fats for different purposes? And are you sure you have not turned the nutritious oil into toxic oil during the cooking process? If you are not sure, please read on.

First of all, do our bodies need fat?
Yes, our bodies need fat, the right fats in right amount.

What are the fats in cooking oil?
All cooking oils have a combination of unsaturated fats(which are monounsaturated fat & polyunsaturated fat) and saturated fat. Some cooking oils have trans-fat.

Most of us know that monounsaturated fat and polyunsaturated fat are good fats that decreases overall cholesterol level especially bad cholesterol level. No doubt trans-fat is the bad fat that increases bad cholesterol level while decreases good cholesterol level. But how about saturated fat? Nutritionists, doctors and media all have told us that saturated fat is bad fat and it causes heart disease. But there are studies/articles(read here and here) showing that saturated fat is essential at small amount. It is not confusing at all. We just have to say NO to trans-fat and limit our fat intake per day.

What is Smoke Point?
Smoke point refers to the temperature where cooking oil starts to break down to glycerol and free fatty acids, and later acrolein. Different cooking oils have different smoke point. But whenever the cooking oil reaches its smoke point, it goes from good to bad. A simple rule of thumb is never overheat oil until it starts to smoke.

I notice that most of the cooking oil labels do not specify their smoke point. The table below can be used as a reference. It presents smoke point for different cooking oils(source from wikipedia). I purposely have it sorted from lower smoke point to higher smoke point.

What are the factors that will decrease the smoke point of a cooking oil?
1. purity of the oil(Blended oils have different smoke points)
2. presence of salt(Salt will reduce the smoke point)
3. presence of foreign properties(For example batter)
4. number of times the oil is used(Smoke point drops when oil is reused)
5. length of time oil is heated(Smoke point drops with time)
6. Storage of oil(Smoke point drops when it is exposed to light and heat?)

Unrefined oils vs Refined oils?
Extracted oils which do not go through any further process are called unrefined oils. These oils are rich, outburst and true about their flavors. It tends to have greater nutritional qualities, but has a lower smoke point compare to refined oil. Refined oils are extracted oils followed by degumming, bleaching, deodorization at high temperature to obtain a clear and bland oil. Hygrogenated vegetable oils are considered refined oils too. Refined oils are more stable in high temperature, however it is chemically processed and less nutritive.

Expeller Pressing vs Cold Pressing?
Expeller pressing is a mechanical process to extract oil. There is no external heat applied to the process. However, the process itself will generate heat, up to or above 120 degrees F(depends on the hardness of the raw material). Cold pressing is done in a heat-controlled environment to keep the temperature below 120 degrees F(50 degrees C).

What is High Oleic?
High Oleic oils, as its name suggests, is the oils which have bred with higher amount of oleic acid for stability. Since high consumption of oleic acid(omega-6 polyunsaturated fatty acids) is believed to increase the risk of breast cancer, it is better to avoid it.

What is vegetable shortening?
Shortening is fat that solid at room temperature. Margarine, substitution of butter is one of the vegetable shortenings. The word "vegetable" made people believe that it is healthier. However, vegetable oils go through hygrogenation process before it can solidify. The chemical process is complicated, but we just have to know that vegetable shortening contains trans-fat, which raises the level of bad cholesterol(LDL) and decreases the level of good cholesterol(HDL).

How do we read olive oil grades?
Extra Virgin: 100% unadulterated olive oil contains no more than 0.8% acidity, highest quality of olive oil
Virgin: 100% unadulterated olive oil contains no more than 2% acidity
Refined: Refined olive oil blend with very little virgin olive oil, "Pure", "Light" and "Extra Light" are in this category.
Pomace: produced from ground flesh and pits left after pressing, and undergo some refining process.

Cooking Method(temperature) vs Cooking Oil?
Basically, we could categorize our cooking methods according to the required temperature to 4 groups. Cold Preparation does not involve heat, therefore could use any oils. Low Heat cooking normally involve boiling liquid, for example blanching and stewing. Baking and sauteing are considered Medium Heat while browning and frying(including deep frying, stir frying, pan frying and shallow frying) are considered High Heat. Chinese cooking which has a lot of "wok hei" falls into high heat category. The cooking oils in the table below are unrefined oils as I do not encourage the use of refined oils. Besides that, I also put some buffer for the smoke point as the smoke point will drop due to several factors mentioned above. Do note that lower temperature groups can use the cooking oils in higher temperature groups but not the other way.

Is Ghee suitable for high temperature cooking?
Ghee is a clarified butter which is widely used in Indian cooking. It is popular with its toasted flavour and high smoke point. But note that ghee has very high saturated fat content Natural ghee does not contain trans-fat, but restaurants may substitute with the cheaper version of "vegetarian ghee", Vanaspati/Dalda(hydrogenated vegetable oil) which contain trans-fat. Therefore, use ghee moderately and avoid "vegetarian ghee".

How many type of oils should we have in a kitchen? 
I would say at least 2 types, or even better 3 types of oils. Choose oils from different category depending on your cooking habits. It is also best to buy different oils each time as they all have different nutritional content. For me, I do a lot of Chinese cookings(sometimes deep frying snacks), therefore I normally have one bottle for high temperature cooking and another bottle(mostly extra virgin olive oil) for cold or low temperature cooking.

 What to note when we shop for oil?
1. If you see "refined" and "hydrogenated" at the label, put them back to the shelf.
2. Look for trans-fat at the nutrition table. Get the one with 0g trans-fat. But this is not true all the time, some manufacturers still claim their cooking oil with 0g trans-fat while their cooking oil actually has 0.5g trans-fat.
2. Watch out for vegetable cooking oils like canola, sunflower, safflower, soybean, corn oil etc. These oils, when they are unrefined, have very low smoke points. So even though some is not labeled as "refined", but the fact is most of them are "refined" to withstand higher cooking temperature.
3. Do not use vegetable shortenings(margarine). They contain trans-fat.
4. Keep a bottle of high smoke point oil for high temperature cooking. Never heat oils above their smoke points.

So it is time to review your cooking oils and shop for new oil if needed.

Have a good weekend and let me know if you like this post. If most of you find this helpful, I am going to do another post on the cooking oils available in the market. And do let me know if you find any incorrect facts in this post, I will verify and fix it.