Smoking Point & Olive Oil

Smoking point is the temperature at which bluish smoke coming up from the cooking oil or fat. The oil begins to break down to glycerol and free fatty acids. The glycerol is then further broken down to acrolein. It is the presence of the acrolein that causes the smoke to be extremely irritating to the eyes and throat. Considerably above the temperature of the smoke point is the flash point, the point at which the vapors from the oil can first ignite when mixed with air.

The smoke point of an oil does tend to increase as free fatty acid decreases and degree of refinement increases. Heating oil produces free fatty acid and as heating time increases, more free fatty acids are produced, thereby decreasing smoke point. The smoke point also marks the beginning of both flavour and nutritional degradation. Therefore, it is a key consideration when selecting a fat for frying.

Oil	Quality	Smoking Point
芥花籽油 Canola (rapeseed) oil	High Oleic	246°C
橄欖油 Olive oil	Extra light	242°C
橄欖油 Olive oil	油渣 Pomace	238°C
花生油 Peanut oil	Refined	232°C
玉米油 Corn oil	Refined	232°C
葵花油 Sunflower oil	Refined	227°C
葡萄籽油 Grapeseed oil		216°C
Olive oil, low acidity	Extra virgin	207°C
芥花籽油 Canola oil	Refined	204°C
橄欖油 Olive oil	Virgin	199°C
橄欖油 Olive oil	Extra virgin	191°C
豬油 Lard		188°C
玉米油 Corn oil	Unrefined	178°C
芝麻油 Sesame oil	Unrefined	177°C
花生油 Peanut oil	Unrefined	160°C
葵花油 Sunflower oil	High Oleic	160°C
奶油 Butter		121-149°C
亞麻仁油 Flax seed oil	Unrefined	107°C
葵花油 Sunflower oil	Unrefined	107°C

Olive oil is composed mainly of the mixed triglyceride esters of (monounsaturated) oleic acid (55-83%) and palmitic acid (7.5-20%) and of other fatty acids. Evidence from epidemiological studies also suggests that a higher proportion of monounsaturated fats in the diet is linked with a reduction in the risk of coronary heart disease. Unlike saturated fats, olive oil lowers total cholesterol and LDL levels in the blood. It is also known to lower blood sugar levels and blood pressure.

Olive oil contains a wide variety of valuable antioxidants that are not found in other oils. Hydroxytyrosol (in extra-virgin olive oil) is thought to be the main antioxidant compound in olives. Hydroxytyrosol's oxygen radical absorbance capacity is 40,000 umolTE/g, which is ten times higher than that of green tea, and two times higher than that of CoQ10. Epidemiological studies suggest that olive oil has a protective effect against certain malignant tumours in the breast, prostate, endometrium and digestive tract. Research has revealed that the type rather than the quantity of fat seems to have more implications for cancer incidence.

Olive oil contains a group of related natural products, called natural phenols, with potent antioxidant properties that give extra-virgin unprocessed olive oil its bitter and pungent taste and are esters of tyrosol and hydroxytyrosol, including oleocanthal and oleuropein. Olive oil is a source of at least 30 phenolic compounds. Oleocanthal is a tyrosol ester and its chemical structure is related to oleuropein that is also found in olive oil. Oleocanthal is a non-selective inhibitor of cyclooxygenase (COX) similar to classical NSAIDs like ibuprofen. 50g of olive oil per day is thought to have the same effect as 1/10 of the adult ibuprofen dose. It has been suggested that long-term consumption of small quantities of this compound from olive oil may be responsible in part for the low incidence of heart disease associated with a Mediterranean diet.

Another health benefit of olive oil seems to be its property to displace omega-6 fatty acids, while not having any impact on omega-3 fatty acids. This way, olive oil helps to build a more healthy balance between omega-6 fats and omega-3 fats.

Olive Oil - Commercial grades
Olive paste is churned slowly or mixed to allow the microscopic oil droplets to concentrate. The oil is extracted by means of pressure (traditional) or centrifugation. After extraction the remnant solid substance, called pomace, still contains a small quantity of oil.

• Virgin means the oil was produced by the use of physical means and no chemical treatment. The term virgin oil referring to production is different from Virgin Oil on a retail label. Virgin olive oils contain the highest levels of polyphenols, antioxidants that have been linked with better health.
• Cold pressed or Cold extraction means "that the oil was not heated over a certain temperature (usually 27 °C) during processing, thus retaining more nutrients and undergoing less degradation."
• First cold pressed means "that the fruit of the olive was crushed exactly one time. The cold refers to the temperature range of the fruit at the time it is crushed." There is no "second" press of virgin oil, so the term "first press" means only that the oil was produced in a press vs. other possible methods.
• Refined means that the oil has been chemically treated to neutralize strong tastes (characterized as defects) and neutralize the acid content (free fatty acids). 
• Pure, Light and Extra-Light are terms introduced by manufacturers for refined oils. They do not have less calories than Extra-virgin oil as implied by the names.
• Olive pomace oil means oil extracted from the pomace using solvents, mostly hexane, and by heat.

Olive Oil - retail grades in IOC member nations

• Extra-virgin olive oil comes from virgin oil production only, contains no more than 0.8% acidity, and is judged to have a superior taste. It is used on salads, added at the table to soups and stews and for dipping.
• Virgin olive oil comes from virgin oil production only, has an acidity less than 1.5%, and is judged to have a good taste.
• Olive oil is a blend of virgin and refined production oil, of no more than 2% acidity. It commonly lacks a strong flavor.
• Olive pomace oil is refined pomace olive oil often blended with some virgin oil. It has the same fat composition as regular olive oil. 

Rancidity, is the chemical decomposition of fats, oils and other lipids.

• Hydrolytic rancidity occurs when water splits fatty acid chains away from the glycerol backbone in triglycerides (fats). More fatty acids are freed from the glycerides, increasing the level of free acidity. 
• Oxidative rancidity is associated with the degradation by oxygen in the air. Oxidation primarily occurs with unsaturated fats.Via a free radical process, the double bonds of an unsaturated fatty acid can undergo cleavage, releasing volatile aldehydes and ketones. This process can be suppressed by the exclusion of oxygen or by the addition of antioxidants. 
• Microbial rancidity refers to a process in which microorganisms use their enzymes such as lipases to break down fat. 

Olive Oil - Culinary use

• Extra virgin olive oil is mostly used as a salad dressing. It is also used with foods to be eaten cold. The higher the temperature to which the olive oil is heated, the higher the risk of compromising its taste.
• Choosing a cold-pressed olive oil can be similar to selecting a wine. The flavour of these oils varies considerably and a particular oil may be more suited for a particular dish.
• Refined olive oils are perfectly suited for deep frying foods and should be replaced after several uses.
•  In time, oils deteriorate and become stale. One-year old oil may be still pleasant to the taste, but it is surely less fragrant than fresh oil. After the first year, olive oil should be used for cooking, not for foods to be eaten cold, like salads.