The RM (Reichert-Meissl) value of ghee is the number of millilitres of 0.1 N alkali needed to neutralise the water-soluble, steam-volatile fatty acids distilled from 5 g of the fat. FSSAI's standard requires at least 24.0, and pure cow and buffalo ghee usually read near 28 or above. Those volatile acids, mostly butyric, are peculiar to milk fat, so a low figure suggests something else is in the jar.
This article covers that one number. For the full list of limits, see our table of FSSAI ghee quality parameters.
At a glance
- FSSAI's standard for milk fat products sets a Reichert-Meissl value of at least 24.0 for ghee, butter oil and anhydrous milk fat alike.
- FSSAI's manual of methods says butyric acid supplies about three-quarters of the RM value and caproic acid about one-quarter.
- A National Dairy Research Institute study found pure cow ghee at 28.60 to 30.36 and pure buffalo ghee at 31.46 to 34.98.
- FSSAI's manual gives ghee from cotton-seed-fed animals an RM value of about 20, and coconut and palm kernel oil about 7.
- In a laboratory study, the RM value alone caught palm olein or sheep body fat only once it made up 15 per cent of the ghee.
What does the RM value of ghee measure?
It measures the short-chain fatty acids that dissolve in water and boil off with steam. FSSAI's manual defines it as the millilitres of 0.1 N alkali that neutralise those acids, distilled from 5 g of ghee under fixed conditions. Butyric acid (C4) supplies about three-quarters of the figure and caproic acid (C6) about one-quarter.
The method in the manual, taken from the Bureau of Indian Standards' 1966 test methods for ghee, runs in four stages:
- Weigh 5.00 g of ghee into a Polenske flask and saponify it with glycerol and sodium hydroxide until the liquid is clear.
- Dissolve the soap in boiled water, acidify it with dilute sulphuric acid, and distil 110 ml in 19 to 21 minutes.
- Cool the distillate and filter it. The water-soluble acids pass through; the insoluble ones stay on the paper.
- Titrate 100 ml of the filtrate with 0.1 N alkali, and run a blank with the same reagents and no ghee.
The result is RM value = 1.10 × (sample titre − blank titre). The 1.10 scales the 100 ml titrated up to the 110 ml distilled (110 ÷ 100 = 1.10). As an illustration with made-up titres, a sample needing 26.8 ml and a blank needing 0.3 ml gives 1.10 × 26.5 = 29.15. The manual allows duplicate determinations to differ by no more than 0.5 units.
Our article on butyric acid in ghee covers the acid itself and what the evidence says about it.
What is the FSSAI limit for the RM value of ghee?
The limit is a minimum of 24.0. It appears in the ghee column of regulation 2.1.8, the FSSAI standard for milk fat products, and the same 24.0 applies to butter oil and anhydrous milk fat. The table gives one figure for all ghee, with no separate value for cow or buffalo ghee and none by region or season.
You will often see 28 quoted instead. FSSAI's own 2015 manual of methods says that "in general, ghee is required to have a R.M. value not less than 28", and IIT Kanpur's virtual dairy laboratory describes pure ghee as "typically around 28 or higher". Those are descriptions of what ghee usually reads. The legal minimum in the standard table is 24.0, and that is the one to check on a report.
What RM values do cow and buffalo ghee usually show?
In the best-documented Indian figures, the upper 20s for cow ghee and the low to mid 30s for buffalo ghee. In a study by the Dairy Chemistry Division of the National Dairy Research Institute, Karnal, pure cow ghee read 28.60 to 30.36, average 29.50, and pure buffalo ghee 31.46 to 34.98, average 33.3. FSSAI's manual gives both about 28 in general.
On those averages buffalo ghee sits 3.8 units higher (33.3 − 29.50 = 3.8), meaning more of the volatile acids came off the same 5 g. Both comfortably clear the legal 24.0. The manual records one natural exception: ghee from the milk of animals fed cotton seed has a much lower RM value, about 20, below the legal minimum with nothing added. It also notes that "no significant seasonal variations have, however, been recorded" for ghee's fat constants.
Why do vegetable oils and animal body fats lower the RM value?
Because they bring almost none of the acids the test counts. FSSAI's manual says the presence of these lower fatty acids "is peculiar to milk fat". Any other fat mixed in dilutes them, so the same 5 g of sample yields less volatile acid and needs less alkali. Of the common vegetable oils, only coconut and palm kernel contain steam-volatile acids, at an RM value of about 7.
So the RM value is an identity test, not a quality one: it says nothing about freshness or moisture. Our guide to reading a ghee lab report shows where the RM value sits among those other lines.
How does the Polenske value pair with the RM value?
It comes from the same distillation. The RM value counts the volatile acids that dissolve in water; the Polenske value counts those that do not, which stay on the filter paper, are dissolved in alcohol and titrated. FSSAI's manual says it is about one-quarter caprylic acid (C8) and three-quarters capric acid (C10).
Coconut and palm kernel oil have a low RM value but a high Polenske value, about 13 against ghee's 1.5 in the manual's general figures. The butyro-refractometer (BR) reading, an optical test, adds a third angle. Here are the three side by side.
| Test | What it counts | FSSAI limit for ghee | Pure ghee, as published | Coconut oil, per FSSAI's manual |
|---|---|---|---|---|
| Reichert-Meissl value | Water-soluble volatile acids: butyric and caproic | 24.0 minimum | Cow 28.60 to 30.36; buffalo 31.46 to 34.98 (NDRI study) | About 7 |
| Polenske value | Water-insoluble volatile acids: caprylic and capric | 0.5 to 2.0 | Cow 2 to 3; buffalo 1 to 1.5 (FSSAI manual) | About 13 |
| BR reading at 40 °C | How the melted fat bends light | 40.0 to 44.0 | Milk fat 40 to 43 (FSSAI manual) | 38 to 39 |
One mismatch is worth knowing. The manual puts cow ghee's Polenske value at 2 to 3, while the legal range stops at 2.0, so a cow ghee reading above 2.0 falls outside the legal range even though the manual describes such values as typical of cow ghee. Coconut oil also reads below milk fat on the BR scale, where most vegetable oils read above 50.
Can adulterated ghee be blended to pass the RM value test?
Yes, within limits, and that is the test's main weakness: a modest amount of foreign fat can go unnoticed. In a 2014 laboratory study from the National Dairy Research Institute, palm olein or sheep body fat added on its own was detected by the RM value only at 15 per cent of pooled cow and buffalo ghee.
Mixtures were harder still. A blend of palm olein and sheep body fat was detectable at 20 per cent (6 + 14) and 30 per cent (9 + 21). Separating the ghee into fractions with a solvent before testing brought the detectable level down to 10 per cent (3 + 7).
A 2020 study from the same institute went further. It examined what it called an "RM-adjuster", a component of a highly manipulated adulterant fat, and analysed its triglycerides by gas chromatography. The authors report:
- Using ISO/IDF limits for cow milk fat, the adulterant was detected down to 7.5 per cent in cow ghee; there are no such limits for buffalo ghee, so that approach could not be used there.
- The adulterant and the RM-adjuster showed large signature peaks in the chromatogram between 4.5 and 6.5 minutes that pure cow and buffalo ghee did not.
- Looking for those peaks, the authors could find the adulterant fat at as little as 0.5 per cent in both cow and buffalo ghee.
Both are laboratory studies, not surveys of ghee on sale. The FSSAI standard goes past distillation too: it sets a fatty acid composition determined by gas-liquid chromatography, and requires β-sitosterol to be absent by a method it describes as one for detecting vegetable oil in ghee.
Does altitude change the RM value result?
Only slightly. FSSAI's manual says Polenske values, "and to a much slighter extent Reichert–Meissl values", come out low when the test is done at low barometric pressure, such as may occur at high altitude. It gives a correction to bring a result back to the value at normal pressure, 760 mm of mercury. It matters mainly when comparing a figure from a hill laboratory with one from the plains.
Every Himdhara jar carries a batch code, and the laboratory report for each batch is on the lab reports page, where you can set its figures against the limits above.
The short version
The RM value counts the short, water-soluble volatile acids, about three-quarters butyric, that milk fat has and other fats almost entirely lack. FSSAI requires at least 24.0, and pure ghee usually reads near 28 or higher. Cotton-seed feeding can pull it to about 20 with nothing added, and coconut or palm kernel oil reads about 7. Read it with the Polenske value and BR reading, and remember that a blended adulterant can slip past it: in laboratory studies, gas chromatography found what the distillation missed.
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 13.3 and 13.5. FSSAI.
- Gandhi K, Upadhyay N, Aghav AD, Lal D, Sharma V (2014). Detection of palm olein and sheep body fat adulteration in ghee (clarified milk fat) using Reichert-Meissl (R.M.) value coupled with solvent fractionation technique. Indian Journal of Dairy Science 67(5).
- Pathania P, Sharma V, Arora S, Rao PS (2020). A novel approach to detect highly manipulated fat adulterant as Reichert-Meissl value-adjuster in ghee (clarified butter) through signature peaks by gas chromatography of triglycerides. Journal of Food Science and Technology 57(1):191–199.
- Virtual Labs, IIT Kanpur. Quality Testing of Butter oil / Ghee. Dairy Technology Virtual Lab.