On this page
- Where are the FSSAI microbiological standards published?
- What do n, c, m and M mean in FSSAI microbiological standards?
- What is the difference between a 2-class and a 3-class sampling plan?
- Worked example: a 3-class sampling plan for pasteurised milk
- What is the difference between process hygiene criteria and food safety criteria?
- What are the FSSAI microbiological limits for dairy?
- How should a lab report FSSAI microbiological results?
- What mistakes do labs make with m and M?
- Where Tanush LIMS fits
- Frequently asked questions
- Sources
FSSAI microbiological standards set limits for organisms such as aerobic plate count, coliforms, Salmonella and Listeria using sampling plans. In these plans, n is the number of units tested, c is how many units may exceed m, m is the lower limit and M is the limit no unit may exceed. Results are classed satisfactory, acceptable or unsatisfactory.
This guide explains the FSSAI microbiological standards for analysts, microbiologists and quality managers in Indian food labs. It uses FSSAI's own definitions and wording, works through a 3-class plan for pasteurised milk, and shows how to report results so that a customer or a Food Safety Officer reads them correctly.
Where are the FSSAI microbiological standards published?
They are in Appendix B of the Food Safety and Standards (Food Products Standards and Food Additives) Regulations, 2011. FSSAI publishes a consolidated Appendix B; the version used here is Version 2, dated 4 November 2024.
Appendix B is organised by food category, each with its own tables. For example, Table 2 covers milk and milk products, Table 3 spices and herbs, and Table 4 fruits and vegetables and their products. Most categories are split into two tables: an "A" table of process hygiene criteria and a "B" table of food safety criteria. Each table also names the reference test methods, usually IS or ISO methods.
FSSAI amends Appendix B from time to time, and the amendment numbers are printed in the text. Always check the current consolidated version on fssai.gov.in before you set up a specification.
What do n, c, m and M mean in FSSAI microbiological standards?
FSSAI defines the four terms in the sampling plan notes of Appendix B:
| Term | FSSAI definition |
|---|---|
| n | Number of units comprising a sample |
| c | Maximum allowable number of units having microbiological counts above m for 2-class sampling plan and between m and M for 3-class sampling plan |
| m | Microbiological limit that separates unsatisfactory from satisfactory in a 2-class sampling plan or acceptable from satisfactory in a 3-class sampling plan |
| M | Microbiological limit that separates unsatisfactory from satisfactory in a 3-class sampling plan |
In plain terms, m and M in microbiology are two limits. A count at or below m is good. A count between m and M is tolerated in a few units, up to c of them. A count above M is never tolerated.
The plan always applies to a set of units from the same batch or lot, not to one container. That is the point most often missed in day-to-day reporting.
What is the difference between a 2-class and a 3-class sampling plan?
A 2-class plan has one limit, m. A 3-class sampling plan has two limits, m and M, and therefore three classes of result. FSSAI's interpretation rules in Appendix B are:
| Plan | Satisfactory | Acceptable | Unsatisfactory |
|---|---|---|---|
| 2-class (n, c and m given) | All values observed are ≤ m | Not used | One or more values observed are > m, or more than c values are > m |
| 3-class (n, c, m and M given) | All values observed are ≤ m | A maximum of c values are between m and M and the rest are ≤ m | One or more values observed are > M, or more than c values are > m |
Two-class plans are used where any count above the limit matters, for example "less than 10 cfu/mL" coliforms in pasteurised milk with c = 0. Three-class plans are used for indicator counts such as aerobic plate count, where some spread between units is expected.
Worked example: a 3-class sampling plan for pasteurised milk
FSSAI Table 2A sets this aerobic plate count criterion for pasteurised, boiled and flavoured milk: n = 5, c = 3, m = 3 × 10⁴ cfu/mL, M = 5 × 10⁴ cfu/mL.
So five units from the lot are tested. Up to three of them may lie above 30,000 cfu/mL, as long as none is above 50,000 cfu/mL and the rest are at or below 30,000 cfu/mL.
| Lot | Results of the 5 units (cfu/mL) | Units above m | Units above M | Classification |
|---|---|---|---|---|
| A | 1.2 × 10⁴, 2.0 × 10⁴, 2.6 × 10⁴, 3.0 × 10⁴, 1.8 × 10⁴ | 0 | 0 | Satisfactory |
| B | 2.1 × 10⁴, 3.4 × 10⁴, 4.6 × 10⁴, 2.8 × 10⁴, 4.1 × 10⁴ | 3 | 0 | Acceptable |
| C | 3.2 × 10⁴, 3.8 × 10⁴, 4.4 × 10⁴, 4.9 × 10⁴, 2.5 × 10⁴ | 4 | 0 | Unsatisfactory (more than c above m) |
| D | 1.5 × 10⁴, 2.2 × 10⁴, 5.3 × 10⁴, 2.0 × 10⁴, 1.1 × 10⁴ | 1 | 1 | Unsatisfactory (one unit above M) |
Three details from this example are worth noting:
- In lot A, the unit at exactly 3.0 × 10⁴ is "≤ m", so the lot is still satisfactory.
- Lot D fails even though four units are well inside m. One unit above M is enough.
- Lot C fails although no unit is above M. Four units above m is more than c = 3.
Before comparing, apply your method's rules for counting colonies and rounding the count. A count rounded differently can move a unit across m.
What is the difference between process hygiene criteria and food safety criteria?
Process hygiene criteria judge the manufacturing process; food safety criteria judge the product. FSSAI's Appendix B says the process hygiene criteria in Table 2A "indicate the acceptable functioning of the production process" and "are not to be used as requirements for releasing the products in the market". They apply at the end of the manufacturing process.
The food safety criteria in Table 2B "define the acceptability of a batch/lot". They apply to the product at the end of manufacturing and to products in the market during their shelf life. Table 2B for dairy covers pathogens such as Salmonella, Listeria monocytogenes, Enterobacter sakazakii, Bacillus cereus and sulphite-reducing clostridia, depending on the product.
When a process hygiene criterion is not met, Appendix B says the food business operator shall check and improve process hygiene using Schedule 4 of the FSS (Licensing and Registration of Food Businesses) Regulations, and ensure that all food safety criteria are met. So a high plate count is a hygiene warning, while a Salmonella detection is a product failure.
What are the FSSAI microbiological limits for dairy?
The FSSAI microbiological limits for dairy are in Table 2A (process hygiene) and Table 2B (food safety) of Appendix B. A few aerobic plate count examples from Version 2:
| Product | n | c | m | M |
|---|---|---|---|---|
| Pasteurised, boiled or flavoured milk | 5 | 3 | 3 × 10⁴ cfu/mL | 5 × 10⁴ cfu/mL |
| Milk powder, skimmed milk powder, dairy whitener and similar powders | 5 | 2 | 3 × 10⁴ cfu/g | 5 × 10⁴ cfu/g |
| Paneer, chhana and chhana-based sweets | 5 | 3 | 1.5 × 10⁵ cfu/g | 3.5 × 10⁵ cfu/g |
| Khoa and khoa-based sweets | 5 | 3 | 2.5 × 10⁴ cfu/g | 7.5 × 10⁴ cfu/g |
Coliforms in pasteurised milk follow a 2-class plan: n = 5, c = 0, less than 10 cfu/mL. Note the unit: liquid milk criteria are per mL, while most other dairy products are per g. Reporting a milk count in cfu/g, or a paneer count in cfu/mL, makes the comparison meaningless.
Sterilised and UHT products are handled differently in Table 2A, so do not apply plate count limits to them by default. Read the row for the exact product before you build the specification.
How should a lab report FSSAI microbiological results?
Report each unit's count, the plan, and the classification in FSSAI's words. A clear report lets the reader see why a lot is satisfactory, acceptable or unsatisfactory.
- Record each of the n units as a separate result, with its own code, in cfu/g or cfu/mL as the table states.
- Name the standard: Appendix B, the table, the product row and the organism.
- Print n, c, m and M beside the results.
- Count how many units are above m and above M.
- Classify the lot as satisfactory, acceptable or unsatisfactory, using Appendix B's interpretation rules.
- If you received fewer than n units, say so. A single unit can be compared with m and M, but it cannot give a lot decision.
For regulatory samples, Appendix B adds rules of its own. It says a set of five samples shall be tested in three different accredited laboratories, the final decision is drawn from the three results, and there is no provision for retesting or re-sampling for microbiological parameters. It also says a food business operator may use other methods for in-house testing, but not for regulatory compliance.
What mistakes do labs make with m and M?
The most common errors are about the lot, the unit and the method:
- Calling a single-unit result "acceptable". Acceptable is a lot classification that needs all n results.
- Treating m as the pass limit and ignoring c, or treating M as the pass limit and ignoring m.
- Using cfu/g for liquid milk, where the criterion is per mL.
- Rejecting a lot outright for a process hygiene result, when Appendix B asks for process correction and checks against food safety criteria.
- Using an in-house or rapid method for a regulatory sample, where Appendix B names reference methods.
Our guide to NABL test report format covers the general report requirements that sit alongside these food-specific rules.
Where Tanush LIMS fits
Tanush LIMS ships FSSAI microbiological standards for dairy, spices, food grain products, cereal products and cooked meat and egg products, with m and M. Like every standard in its library, they load as drafts that your technical manager reviews and activates before any limit prints.
On the review screen, a 3-class limit reads "Acceptable: m = 3 × 10⁴ cfu/mL (n = 5, c = 3)" and "Limit: M = 5 × 10⁴ cfu/mL (n = 5, c = 3)". A result between m and M shows the amber badge "Within permissible †"; above M it shows "Does not comply". The report prints separate m and M columns and the footnote "Results marked † are above m but within M (3-class sampling plan): acceptable for this unit within the number c of units allowed between m and M." The lot decision across all n units stays with your reviewer. See Tanush LIMS for food labs or book a demo.
Frequently asked questions
What is m and M in microbiology?
They are the two limits of a 3-class sampling plan. FSSAI defines m as the limit separating acceptable from satisfactory, and M as the limit separating unsatisfactory from satisfactory. A unit above M makes the lot unsatisfactory; units between m and M are allowed only up to c.
What does c = 0 mean in FSSAI standards?
It means no unit may exceed m. With c = 0 the plan behaves as a 2-class plan: every one of the n units must be at or below m for the lot to be satisfactory, and any unit above m makes it unsatisfactory.
Is "acceptable" a pass under FSSAI microbiological standards?
Yes. In a 3-class plan, "acceptable" means a maximum of c units lie between m and M and the rest are at or below m. It is a conforming result, but it indicates more variation than a satisfactory lot.
Can I judge a lot from one sample?
No. A lot decision needs all n units of the plan. With one unit you can only report whether that unit is at or below m, between m and M, or above M.
Do process hygiene criteria apply to products in the market?
No. FSSAI says process hygiene criteria apply at the end of the manufacturing process and are not requirements for releasing products. Food safety criteria apply at the end of manufacturing and during shelf life in the market.
Which test methods should a lab use?
Use the reference methods Appendix B names for each organism, usually IS or ISO methods, in their latest version. FSSAI also allows its Manual of Methods of Analysis of Foods (Microbiological Testing) to be referred to alongside them.
Sources
- FSSAI, Appendix B, Food Safety and Standards (Food Products Standards and Food Additives) Regulations, 2011, Version 2, 04.11.2024: Table 2A and 2B, sampling plan definitions, interpretation of results, stage of application, sampling guidelines and reference methods.
- FSSAI, Gazette notification on microbiological standards for fruits and vegetables and their products, April 2018: sampling plan definitions and interpretation table.