The butyro-refractometer (BR) reading of ghee is a measure of how strongly melted ghee bends light, read at 40 °C on an instrument scale designed for butter fat. FSSAI's standard for milk fat products requires ghee to read between 40.0 and 44.0; a result outside that range suggests a fat other than milk fat. It is a screening test, and it has known blind spots.
Our guide to ghee quality parameters lists every FSSAI limit for ghee. This article takes one line from that table and explains it: what the number is, how a laboratory gets it, what moves it, and what it cannot tell you.
At a glance
- FSSAI regulation 2.1.8, the Standard for Milk Fat Products, sets a butyro-refractometer reading at 40 °C of 40.0 to 44.0 for ghee, the same range as for butter oil and anhydrous milk fat.
- FSSAI's Manual of Methods of Analysis (2015) gives milk fat a general BR reading of 40 to 43 and most vegetable oils and fats a reading above 50.
- The same manual puts animal body fats at 44 to 51, coconut oil at 38 to 39 and palm oil at 39 to 40, which is why the test cannot catch all of them.
- In a 2017 Indian Journal of Dairy Science study, soybean oil read 63.50 against 41.76 for pure cow milk fat, but buffalo depot fat (45.81) went undetected in cow milk fat at levels up to 15 per cent.
- The FSSAI manual allows duplicate readings to differ by no more than 0.1, and corrects the reading by 0.55 for each degree the instrument is away from 40 °C.
What is the butyro-refractometer reading of ghee?
It is the refractive index of melted ghee expressed on the butyro scale. Light slows and bends as it passes from air into a fat, and how much it bends depends on the fat's chemistry. An Abbe refractometer reports the true refractive index; a butyro-refractometer reports the same property on an arbitrary scale built for butter fat.
FSSAI's Manual of Methods of Analysis of Foods for milk and milk products (2015) explains why the reading is taken at 40 °C: ghee is often solid or semi-solid at room temperature, and at 40 °C the sample is clear and transparent. The manual's conversion table links the two scales. A BR reading of 40.0 corresponds to a refractive index of 1.4524, 42.0 to 1.4538 and 44.0 to 1.4552, so the whole legal band for ghee spans less than three thousandths of a refractive-index unit.
What BR reading does FSSAI allow for ghee?
Between 40.0 and 44.0 at 40 °C. That figure is in the composition table of regulation 2.1.8, the Standard for Milk Fat Products, in Chapter 2.1 of FSSAI's food product standards. The same range applies to milk fat, butter oil, anhydrous milk fat and anhydrous butter oil, and the extracted fat from butter and khoa must meet it too.
The current table carries one national range for ghee, with no separate figure for cow or buffalo ghee and no regional variant. Older regional limits survive elsewhere in the manual. Its test for foreign fat in milk, where fat is first separated from a milk sample, says foreign fat may be suspected if the reading is above 42 in non-cotton-tract areas or above 45 in cotton-tract areas. That note applies to fat taken from milk, not to the ghee standard, so do not read it against a ghee report.
The legal range is wider than the manual's description of normal milk fat, which is 40 to 43. A ghee reading of 43.5 passes the standard while sitting above the typical band.
How is the BR reading taken?
By melting and filtering the ghee, placing a few drops between the instrument's two prisms held at 40 °C, and reading where the light and dark halves of the field meet on the scale. FSSAI's manual, which follows the Bureau of Indian Standards method IS 3508, sets out each step, and most of them exist to keep water, particles and temperature from distorting the result.
- Melt the ghee in a water bath at no more than 50 °C and filter it hot through a fluted filter paper so that it is bright, clear and free of water and suspended matter.
- Check the instrument with a calibration liquid of known refractive index at 40 °C, with hot water circulating to hold the prisms at 40 ± 1 °C.
- Place a few drops of ghee on the prism so that it fills the space between the two prisms with no air bubble, and close them firmly.
- Wait two to five minutes until the sample and instrument are at the same temperature, and take two or more readings to confirm it is steady.
- Turn the compensator until the coloured band at the border becomes a sharp, colourless line, and read the BR value directly from the scale.
Temperature matters because the reading falls as the sample warms. If the instrument is not exactly at 40 °C, the manual adds 0.55 to the observed reading for each degree above 40 °C and subtracts 0.55 for each degree below, and it says the temperature should not normally deviate by more than 2 °C. A reading of 41.0 taken at 42 °C therefore becomes 41.0 + (2 × 0.55) = 42.1. Duplicate readings on the same sample should not differ by more than 0.1.
Why do vegetable oils push the reading up?
Because the reading rises with unsaturation and with longer fatty acid chains, and milk fat is unusual in its short-chain fatty acids. FSSAI's manual says a double bond raises the refractive index, and that the reading rises when short-chain fatty acids fall or when longer saturated or unsaturated fatty acids increase, especially unsaturated ones.
The manual's examples make the point at the level of single fatty acids. Stearic acid has a lower refractive index than oleic acid, which in turn is lower than linoleic acid. Among saturated fatty acids from butyric to stearic, the index climbs steeply over the short chains and then levels off. The manual also notes that the presence of these lower fatty acids is peculiar to milk fat; it is what the Reichert-Meissl value counts.
Laboratory figures show how large the gap can be. In a 2017 study in the Indian Journal of Dairy Science, soybean oil gave an average BR reading of 63.50, against 41.76 for pure cow milk fat and 40.75 for pure buffalo milk fat. The manual puts most vegetable oils and fats above 50. The manual also warns about one factor that pulls the other way: free fatty acids considerably lower the refractive index.
| Fat | BR reading as reported | Source |
|---|---|---|
| Milk fat, general values | 40 to 43 | FSSAI manual, 2015 |
| Pure cow milk fat, study average | 41.76 | Kumar and others, IJDS, 2017 |
| Pure buffalo milk fat, study average | 40.75 | Kumar and others, IJDS, 2017 |
| Vegetable oils and fats, most | Above 50 | FSSAI manual, 2015 |
| Soybean oil, study average | 63.50 | Kumar and others, IJDS, 2017 |
| Coconut oil | 38 to 39 | FSSAI manual, 2015 |
| Palm oil | 39 to 40 | FSSAI manual, 2015 |
| Animal body fats | 44 to 51 | FSSAI manual, 2015 |
| Buffalo depot (body) fat, study average | 45.81 | Kumar and others, IJDS, 2017 |
The manual's figures are general reference values; the study figures are averages for the specific samples that one laboratory tested. Neither is a limit.
Why can the BR reading miss tallow, lard, coconut and palm oil?
Because their readings sit too close to milk fat's. FSSAI's manual puts animal body fats at 44 to 51, which begins exactly where the legal range for ghee ends, so a modest amount mixed into ghee can leave the blend inside 40.0 to 44.0. Coconut oil and palm oil read at or just below milk fat, and the manual names them as exceptions the test does not catch.
The 2017 study shows the problem with body fat directly. Buffalo depot fat, the body fat of the buffalo, was added to cow and buffalo milk fat at 5, 10 and 15 per cent, and stayed undetectable by BR reading at every level in cow milk fat. In buffalo milk fat, neither soybean oil nor depot fat was detectable on its own at any level studied, except soybean oil at 15 per cent. Mixtures of the two were easier to catch, and the authors report that a dry fractionation step lowered the detection limit for those mixtures.
Palm oil is less clear-cut. A 2025 laboratory study in the International Journal of Food Science spiked ghee with refined palm oil and found the BR reading rose in step with the amount added, from 42.96 for the pure ghee to 43.18 at 5 per cent, 43.75 at 10 per cent, 44.11 at 15 per cent and 44.46 at 20 per cent. The difference became significant only from 10 per cent, and the authors concluded that BR reading was not an effective way to detect palm oil in ghee at low levels. That direction does not match the manual's reference range for palm oil, which is one more reason not to rest a verdict on this test alone.
The wider picture of what gets added to ghee, and which tests catch each adulterant, is in our article on ghee adulteration in India.
How should you read the BR line on a batch report?
Check three things: that the reading was taken at 40 °C, that it falls between 40.0 and 44.0, and that the other identity values on the same report also pass. A BR reading inside the range is consistent with milk fat but does not prove it; a reading above 44.0 fails the standard and points to a foreign fat.
- The temperature. The FSSAI limit is for a reading at 40 °C. A figure given at another temperature, or as a true refractive index, needs converting before you compare it.
- The band, not the midpoint. There is no ideal value inside 40.0 to 44.0. A reading of 41 is not "purer" than one of 43.
- The neighbours. Read the BR line with the Reichert-Meissl value, Polenske value, Baudouin test and β-sitosterol result. FSSAI requires all of them for ghee, and no one of them settles the question alone.
- The batch code. A report describes the batch it names. Our guide to reading a ghee lab report covers matching the code, the laboratory and the scope of the tests.
Every Himdhara jar carries a batch code, and the report for each batch, beginning with batch HIM101, is published on the lab reports page before the batch ships. Set its identity values against the range above; we do not repeat batch figures here, so the report stays the single source for them.
The short version
The butyro-refractometer reading is the refractive index of melted ghee on an instrument scale, taken at 40 °C. FSSAI requires ghee to read 40.0 to 44.0, and its methods manual describes normal milk fat as 40 to 43. Most vegetable oils read above 50, so a high reading flags them, but animal body fats start at 44 and coconut and palm oil read close to milk fat, so the test can miss them. Treat the BR line as one check among the identity values on a report, never as proof of purity by itself.
Sources
Further reading behind the figures above. Himdhara's own numbers — yields, batch results — come from our production records and the batch reports on the lab reports page.
- Food Safety and Standards Authority of India. Food Safety and Standards (Food Products Standards and Food Additives) Regulations, 2011: Chapter 2.1, Dairy products and analogues, regulation 2.1.8, Standard for Milk Fat Products. FSSAI.
- Food Safety and Standards Authority of India (2015). Manual of Methods of Analysis of Foods: Milk and Milk Products, sections 1.2.9 and 13.3. FSSAI.
- Kumar A, Upadhyay N, Gandhi K, Naik SN, Sharma V (2017). Detection of adulteration in anhydrous milk fat (ghee) using season variation in Butyro-refratometer reading studied by employing dry fractionation technique. Indian Journal of Dairy Science 70(5).
- Ramani A, Hazra T, Tarafdar A, Sirohi R, Das A, Dey S, Kumar Y (2025). Comprehensive Studies on Detection of Palm Oil Adulteration in Clarified Milk Fat (Ghee). International Journal of Food Science.