Soy bean oil; degumming and refining process

Soy bean oil refining refers to the process of using oil refining equipment to remove impurities from crude oil, extract essence, and purify it. The impurities contained in unrefined soybean oil mainly include cake crumbs, peptized impurities, free fatty acids, pigments, and odor substances. The reason for refining soy bean oil is to reasonably filter out the cake crumbs, peptic impurities, free fatty acids, pigments and odor substances contained in the pressed or leached crude oil. Therefore, it is more suitable for edible and storage, and enhances the edible value and market value of soybean oil.

The presence of impurities in crude soy bean oil not only affects the edible value and safe storage of the oil, but also brings difficulties to the deep processing of soybean oil. The purpose of refining is not to remove all the impurities in the oil, but to remove the harmful and unhelpful impurities such as gossypol, protein, phospholipids, mucus, moisture, etc., and beneficial “impurities” , Such as tocopherols, etc. should be retained.

CRUDE SOY BEAN OIL REFINING PROCESS

The process of refining crude soy bean oil involves series of steps from degumming, neutralizing, bleaching to deodorizing.

DEGUMMING OF SOY BEAN OIL

Crude soy bean oil contains two kinds of phospholipids: hydratable and non-hydratable. Degumming involves adding of food grade acid(phosphpric acid, citric acid)  into the oil, which transforms non-hydratable phospholipids into hydratable. All hydratable phospholipids are then removed by the addition of water (hydration), which causes agglomeration of the phospholipids into flakes, which are subsequently centrifuge separated. Phospholipid removal is always the first step of vegetable oil processing. It can be done together with free fatty acid (FFA) removal, which carries out the process of neutralization, which is an optional feature of the degumming technology. Hydratable gums can be removed from the oil by water-degumming and non-hydratable gums are removed by addition of phosphoric acid.

NEUTRALIZATION AND WASHING OF SOY BEAN OIL

The process of neutralization f soy bean oil involves breaking of bonds in free fatty acids using caustic soda (NaHO) and making the oil free from moisture, hexane, sludge e.t.c. after the washing process.

Process of Neutralization

The quantity of NaHO to be used is calculated and dissolved in water depending on the percentage of FFA in the oil.

Steam is sent through the steam line to the neutralizer which already contains the desired quantity of oil to be neutralized

Heat the oil to 40-45 degree celcius

At 68-70 degree celcius stop heating but keep stirring the oil

Add NaHO (calculated quantity)

The oil is now neutralized

Stop stirring

Allow oil to settle for 5 minutes

Wash down process

Add hot water and allow to settle for 3 hours

Drain the soap

Washing process

Heat oil t 85 degree celcius with stirrer on

Stop stirring and heating

Allow to settle for 5minutes

Add hot water and allow to settle for 45minutes

Drain

Repeat the process three times at higher temperatures until the oil stops foaming and is well washed.

phenolptaleine indicator is used in drops, slight pink color shows the oil is well neutralized and colourless shows the oil is well washed.

BLEACHING OF SOY BEAN OIL

Oil bleaching is a step in the process of crude oil refining. In the bleaching technology, bleaching earth is applied to crude oil, minimizing its content of pigments (e.g., carotenes and chlorophylls), heavy metals, and the phosphorus remaining after degumming. This improves the appearance and taste of the oil.

Bleaching process

Vacuum is created to -760mmHg in the bleacher

Oil is sent from the neutralizer to the bleacher

Heat the oil to 110-115 degree celcuis while stirring and build up the vacuum back to -760mmHg

Stop heating but keep stirring

Add the bleaching earth (tonsil) and keep stirring for 20minutes

Break the vacuum and release pressure

Send the oil to the Pressure Leaf Filter (PLF) which separates the oil from the spent earth which is steam dried and discarded

Then send the oil to the polish filter which removes any remains of bleaching earth

DEODOURIZING OF SOY BEAN OIL

Vacuum is built in the deodourizer to -760mmHg

Bleached oil is sent to the deodorizer

The thermopac is started which heats the oil to 120-125 degree celcius

Steam is then sent t keep heating the oil to 250-300 degree celcius

The booster is started and the steam valves are opened and direct steam is sent to the deodorizer which evaporates along side the aldehydes, ketones and poisonous gases hence the oil is heated above boiling point of water

The oil is allowed to rest for 5minutes

If the oil is well deodorized,

Break the vacuum and open the outlet valves to send the oil to the cooler

Cool the oil to room temperature to avoid reverse of colour

Send the oil to the polished filter t remove remaining impurities

Send the polished and deodorized oil the deodorized oil tank

Add vitamin A

Finally send the oil to the refined  oil tank

The oil is now well refined and ready for packaging and distribution or storage.