Oil quality is judged partly by free fatty acid (FFA) content and partly by oxidation markers such as peroxide value (PV) and anisidine value. The bleaching step plays an important role in oxidation control. This guide explains what activated bleaching earth can and cannot do for these parameters.
Peroxide Value and the Bleaching Step
Primary oxidation produces peroxides, measured as peroxide value. Activated bleaching earth adsorbs and decomposes peroxides during contact, so bleached oil typically shows a lower PV than the incoming oil. Effective bleaching therefore improves the oxidative starting point for deodorisation.
Secondary Oxidation Products
Peroxides break down into aldehydes and ketones (secondary oxidation products), measured by anisidine value. Bleaching earth adsorbs many of these polar carbonyl compounds, improving flavour stability and reducing the load on the deodoriser.
What About Free Fatty Acids?
Bleaching earth has limited direct effect on FFA. FFA is mainly reduced by alkali neutralisation or, in physical refining, by steam stripping during deodorisation. However, by removing pro-oxidant trace metals, bleaching earth slows the future development of FFA during storage.
Trace Metals: The Hidden Driver
Iron and copper are powerful pro-oxidant catalysts. Even at parts-per-million levels they accelerate peroxide formation. Activated bleaching earth adsorbs these metals, which is one of its most valuable contributions to long-term oil stability.
Getting the Most from Bleaching
Using a high-surface-area, correctly acidic earth such as Bleach Master maximises peroxide decomposition and metal removal, giving deodoriser feed with a clean oxidative profile.
Frequently Asked Questions
Does bleaching earth lower peroxide value?
Yes. Activated bleaching earth adsorbs and decomposes peroxides during contact, so bleached oil generally has a lower peroxide value than the incoming oil.
Does bleaching earth reduce free fatty acids?
Only indirectly. FFA is mainly removed by neutralisation or steam stripping. Bleaching earth removes pro-oxidant metals that would otherwise accelerate FFA formation in storage.
What is anisidine value and does bleaching help?
Anisidine value measures secondary oxidation products (aldehydes/ketones). Bleaching earth adsorbs many of these polar carbonyls, improving flavour stability and easing the deodorisation load.
Why does trace metal removal matter for oxidation?
Iron and copper catalyse oxidation even at trace levels. Removing them during bleaching significantly slows peroxide and off-flavour development during the oil's shelf life.
Need Activated Bleaching Earth for Your Refinery?
Contact Umiya Minerals for product samples, technical data sheets, and bulk pricing. We supply pan-India from Bhuj, Gujarat.