How to Choose Bleaching Earth for Edible Oil Refining

What bleaching earth does in edible oil refining

Choosing bleaching earth for edible oil refining starts with understanding what the adsorbent has to remove. Bleaching is the refining step in which an adsorbent clay is mixed with hot, degummed or neutralised oil under vacuum and then filtered out. Despite the name, colour reduction is only part of the job.

A good bleaching earth adsorbs pigments such as carotenoids and chlorophyll. It also removes trace metals, residual soaps and phospholipids, and primary and secondary oxidation products. Removing these impurities protects the oil during deodorisation and supports its flavour and oxidative stability. Bleaching performance is therefore judged on several results, not colour alone.

Types of bleaching earth

Most bleaching earths are produced from bentonite-type clays rich in montmorillonite. They fall into three broad groups.

• Natural or neutral bleaching earth: clay that is dried and ground without acid treatment. It has moderate activity and a near-neutral pH, and is used for lightly coloured oils or where acidity must be kept low.
• Acid-activated bleaching earth: clay treated with mineral acid to increase surface area and open its pore structure, then washed, dried and milled. Activation markedly increases its capacity to adsorb chlorophyll and other pigments. Most edible oil refineries use activated grades.
• Low free acid grades: activated earths processed to reduce residual acidity. They are used where acid-catalysed reactions in the oil are a concern, and some refiners evaluate them as one of several measures for managing process contaminants such as 3-MCPD esters and glycidyl esters.

Key specifications and what they mean

A Technical Data Sheet for bleaching earth typically lists the parameters below. Ranges vary widely by product type, so treat any figure as guidance and rely on the guaranteed limits on the supplier's TDS and batch CoA.

Ask how bleaching efficiency was measured, which reference oil was used and at what dosage. A colour result means little without those details.

Matching the earth to your oil

Different oils carry different impurity loads, so the best grade for one oil is rarely the best for all. The points below are general tendencies rather than rules.

• Soybean, rapeseed and canola oil: chlorophyll removal is often the main challenge, which normally calls for an activated grade with good chlorophyll capacity.
• Palm oil: in physical refining much of the carotene is broken down by heat during deodorisation, so the earth is chosen mainly for removing trace metals, residual phosphatides and oxidation products that affect colour stability.
• Sunflower and corn oil: usually lighter in colour, so moderate activity may be enough, with attention to waxes and filtration behaviour.
• Rice bran and other speciality oils: impurity profiles vary considerably, trials are essential, and low free acid grades are often evaluated where acidity is a concern.
• Oils for further processing such as hydrogenation: thorough removal of soaps, phosphorus and metals helps protect downstream catalysts.

Dosage, process conditions and laboratory trials

Bleaching earth dosage typically ranges from about 0.5 to 2.0 % of oil weight, depending on oil quality and the target colour. Bleaching is commonly carried out at around 90–110 °C under vacuum, with a contact time of roughly 20–40 minutes, followed by filtration. These are general industry figures; your own process sets the optimum.

The most reliable way to compare products is a controlled laboratory bleaching trial. A sound trial follows a few simple rules.

• Use the same batch of pretreated oil for every sample.
• Test each earth at two or three dosages to build a dose-response curve.
• Keep temperature, vacuum, contact time and agitation identical across samples.
• Measure Lovibond colour, chlorophyll, peroxide value and free fatty acids before and after, using AOCS or equivalent methods.
• Where possible, deodorise the bleached samples, because colour after deodorisation is what the end customer sees.
• Record filtration time and oil retention, since a lower-cost earth that holds more oil can cost more in lost yield.

Filtration, handling and spent earth

Filtration rate matters in a busy refinery. Earths with a high fines content can blind filter leaves and lengthen cycles, so some refiners pair bleaching earth with a filter aid such as diatomaceous earth.

Store bleaching earth in dry, covered conditions and keep bags sealed until use, because moisture pickup changes performance. Handle the powder with the dust controls described in the Safety Data Sheet. Spent bleaching earth contains retained oil and can self-heat if left in heaps, so it should be handled and disposed of according to local regulations.

Bleaching earth used in edible oil refining is subject to food-related regulations that vary by country. Customers should verify suitability for their application and confirm local regulatory requirements before use.

What to ask your supplier

Before approving a new bleaching earth, request the information needed to compare it fairly and to control every later delivery.

• A Technical Data Sheet with typical properties, guaranteed limits and test methods.
• A batch Certificate of Analysis for every lot delivered.
• An MSDS/SDS covering handling, storage and disposal.
• Samples large enough for a full dose-response trial.
• The activation type and residual acidity of the grade offered.
• Packaging suited to your dosing system, whether manual bag tipping or bulk bag discharge.

How Obsidian Minerals can help

Obsidian Minerals manufactures bleaching earth in Gujarat, India. The range includes Standard Bleaching Earth for edible oil refining and a Low Free Acid Grade for speciality oils, alongside a High Activity Grade intended for mineral oil purification. Filter-grade diatomaceous earth is also available as a filter aid.

Products are tested in an NABL-accredited laboratory under ISO 9001 certified processes, and each shipment includes a batch CoA, Technical Data Sheet and MSDS/SDS. Packing options are 25 kg or 50 kg HDPE or paper bags and 1 MT or 1.2 MT jumbo (FIBC) bags, with custom packaging on request. Samples are available on request for your own bleaching trials, and custom grades can be developed with customers.

Frequently asked questions