Introduction

Sifting is a simple-looking operation, but it is important in pharmaceutical manufacturing.

During manufacturing, powders and granules may contain lumps, oversized particles, or foreign particles. Sifting helps separate particles according to size and provides a more uniform material for the next processing step.

In the pharma industry, the sieve used for a material should not be selected just because a particular mesh size is commonly used. The required sieve size should be based on the approved process, material specification, particle-size requirement, and validated procedure.

For example, a sieve may be used during raw material dispensing, before blending, after milling, or during granulation-related operations. The exact sieve size can therefore vary from one product or process to another.

GMP requires manufacturing operations to be clearly defined, controlled, documented, and suitable for consistently producing products of the required quality.

What Is Sifting in Pharmaceutical Manufacturing?

Sifting is the process of passing pharmaceutical powder or granules through a specified sieve to separate particles based on their size.

The sieve contains openings of a defined size. Smaller particles can pass through the openings, while larger particles are retained.

In simple words:

Sifting removes oversized particles and lumps and helps achieve the required particle-size distribution.

It may be performed manually using a sieve or with equipment such as a vibratory sifter, depending on the batch size and manufacturing process.

Why Is Sifting Important in Pharma?

Sifting is performed for several practical reasons:

To remove lumps from powders
To remove oversized particles
To improve particle-size uniformity
To break soft agglomerates where permitted by the process
To improve material flow during subsequent processing
To prevent unwanted foreign material from entering the next stage
To maintain consistency between batches
To meet the specified particle-size requirement

Particle size can influence downstream processing. For example, granule size can affect powder flow and tablet-die filling, so controlling particle size can be important for consistent manufacturing performance.

However, sifting should not be treated as a substitute for milling or other particle-size reduction operations. If the material contains hard or oversized particles that require size reduction, the approved manufacturing process should define the appropriate operation.

If you are learning pharmaceutical manufacturing, these topics are closely connected with sifting:

Sifting Procedure in Pharmaceutical Manufacturing

The following is a general GMP-oriented procedure. The actual steps, sieve number, equipment, and acceptance criteria should always follow the approved site SOP and batch manufacturing record.

Step 1: Check the Manufacturing Documents

Before starting the activity, verify:

Product name
Batch number
Material name
Material code
Quantity to be sifted
Required sieve size
Sifting equipment, if applicable
Relevant SOP
Batch manufacturing or dispensing instructions

Do not select a sieve based only on personal experience.

Step 2: Verify Line Clearance

Before starting sifting, check that the area and equipment are properly cleared.

Confirm that:

Previous product/material has been removed.
Previous labels and documents are removed.
The area is clean.
The sifting equipment is clean.
The required sieve is available.
No unrelated material is present.
Equipment status labels are correct.

The line-clearance requirements should be defined in the site’s approved procedure.

Step 3: Verify the Sieve

Before use, inspect the sieve carefully.

Check:

Correct sieve number/size
Sieve identification number, if applicable
Sieve integrity
Mesh condition
Frame condition
No visible damage
No holes or broken wires
No powder or foreign material trapped in the mesh
Cleaning status
Calibration/inspection status where applicable

A damaged sieve should not be used.

Important: A sieve with a damaged or broken mesh can allow unwanted oversized particles to pass into the processed material.

Step 4: Assemble the Sieve

If a mechanical sifter is being used, assemble the sieve according to the equipment SOP.

Make sure:

The sieve is correctly positioned.
The gasket/seal is properly fitted where required.
Clamps are secured.
The equipment is correctly assembled.
The collection container is properly positioned.
The system is ready for operation.

For manual operation, place the sieve securely over the clean and identified receiving container.

Step 5: Transfer the Material

Transfer the required quantity of material into the sieve.

Avoid dropping large quantities at once.

Overloading the sieve can reduce the efficiency of sifting and may increase the possibility of mesh blockage.

For dusty materials, use the approved dust-control arrangements and avoid unnecessary handling that can generate airborne powder.

Step 6: Perform Sifting

Start the sifting operation according to the approved SOP.

For mechanical sifting, use the specified:

Sifter
Speed/frequency
Sifting time
Feed rate
Screen configuration

For manual sifting, gently move the material through the sieve as specified by the procedure.

Do not force material through the mesh by using excessive pressure or unsuitable tools unless the approved procedure specifically permits it.

The purpose is to pass material through the sieve—not to damage the mesh.

Step 7: Monitor the Sifting Operation

During operation, observe the process for abnormal conditions.

Look for:

Excessive vibration
Unusual noise
Mesh blockage
Material leakage
Dust leakage
Sieve damage
Abnormal accumulation of material
Equipment malfunction

If an abnormality is observed, stop or hold the operation according to the applicable SOP and inform the responsible department.

Step 8: Collect the Sifted Material

Collect the sifted material in a clean, suitable, and properly identified container.

The container should be labelled according to the site’s material identification system.

Typical information may include:

Product/material name
Batch number
Material code
Stage/process
Quantity
Status
Date
Operator identification, where required

Step 9: Handle the Retained Material

The material retained on the sieve should not automatically be discarded.

First determine what the approved procedure says.

Depending on the process, retained material may be:

Collected separately
Reprocessed
Sent for milling
Investigated
Rejected
Disposed of

The decision should be based on the approved procedure and material requirements.

Step 10: Check and Record the Quantity

Where required, record the quantity before and after sifting.

If the process requires reconciliation, compare:

Quantity before sifting vs. quantity after sifting + retained/rejected material

Any unexplained discrepancy should be investigated according to the applicable procedure.

Step 11: Complete the Documentation

Record the required details in the relevant manufacturing or equipment records.

Depending on the process, documentation may include:

Date and time
Material name
Batch number
Sieve number
Sieve identification number
Equipment identification
Quantity processed
Operator name/signature
Checker verification
Sifting observations
Retained quantity, if applicable

Good documentation is an important part of GMP control.

Step 12: Clean the Equipment

After completing the operation:

Stop the equipment.
Remove remaining material.
Dismantle the sieve/equipment as per SOP.
Clean the sieve and equipment.
Inspect the mesh again.
Ensure no product remains trapped.
Dry the equipment if required.
Store the sieve in the designated location.
Apply the appropriate clean/status label.

Cleaning should be performed according to the approved cleaning SOP.

How to Select the Correct Sieve Size?

This is one of the most important points in pharmaceutical sifting.

There is no single sieve size that is correct for every pharmaceutical powder or granule.

The sieve should be selected based on:

1. Material Characteristics

Consider:

Powder or granule
Particle size
Flow characteristics
Moisture
Tendency to form lumps
Cohesiveness
Material sensitivity

A fine powder may require a different screen from a coarse granulation.

2. Product Specification

The product or material specification may define particle-size requirements.

The selected sieve should therefore match the approved specification or manufacturing process.

3. Manufacturing Stage

Sieve selection can change depending on where the operation occurs.

For example:

Raw material → Sifting → Blending

may use a different sieve requirement from:

Wet granulation → Drying → Milling → Sifting → Final blending

Therefore, never assume that the same sieve should be used at every stage.

4. Process Requirement

The manufacturing process may specify the exact sieve size.

For example, an approved BMR may state:

“Pass the dried granules through the specified sieve.”

In such a situation, the operator should follow the approved instruction rather than choosing another sieve based on personal judgement.

Understanding Mesh Size

The term mesh refers to the number of openings per linear inch of a sieve.

As a general principle:

Higher mesh number = smaller sieve opening.

For example, a 60-mesh sieve has smaller openings than a 40-mesh sieve.

But there is an important point:

Do not treat mesh number and aperture size as exactly interchangeable across every sieve standard.

For technical specifications, the nominal aperture size in micrometres (µm) is often a more useful way to identify the actual opening.

Pharmacopoeial powder classifications are also expressed using nominal sieve aperture sizes. For example, Indian Pharmacopoeia powder grades use sieve numbers together with nominal aperture sizes.

Common Sieve Sizes Used in Pharmaceutical Manufacturing

The following sizes are commonly encountered in pharmaceutical operations, but they are examples, not universal manufacturing requirements:

Sieve	Approximate opening*	Typical consideration
20 mesh	~850 µm	Coarser particles/granules
30 mesh	~600 µm	Coarse material
40 mesh	~425 µm	Intermediate particle size
60 mesh	~250 µm	Finer material
80 mesh	~180 µm	Fine material
100 mesh	~150 µm	Finer powders

*Approximate values can vary with the sieve standard and specification. For GMP manufacturing, use the aperture specified in the approved procedure rather than relying only on a mesh-number conversion.

Sifting vs. Sieve Analysis

These two terms are sometimes confused.

Sifting

Sifting is a manufacturing operation used to pass material through a specified sieve.

Example:

A raw material is sifted through a specified sieve before blending.

Sieve Analysis

Sieve analysis is a testing/particle-size analysis technique used to determine how particles are distributed across different size ranges.

For example, a sample may be passed through several sieves and the quantity retained on each sieve may be measured.

A pharmaceutical sieve-analysis procedure may use a series of sieves such as 16, 20, 40 and 60 mesh to determine the distribution of granule sizes.

So:

Sifting = processing activity

Sieve analysis = testing/measurement activity

Manual Sifting vs. Mechanical Sifting

Manual Sifting

Manual sifting may be suitable for small quantities or where the approved process specifically requires it.

Advantages:

Simple operation
Easy to perform
Suitable for small quantities

Limitations:

Operator dependent
More time-consuming
Difficult to maintain the same conditions for large batches

Mechanical Sifting

Mechanical or vibratory sifters are commonly used when larger quantities need to be processed.

Advantages include:

Better process consistency
Higher throughput
Reduced manual handling
More suitable for larger quantities

However, the equipment must be operated according to its approved SOP and validated/qualified conditions where applicable.

Important Precautions During Sifting

1. Never use a damaged sieve

Inspect the mesh before use.

A broken mesh can result in unintended particle passage and possible contamination.

2. Use the correct sieve

Do not change the sieve size without following the approved change-control/process requirements.

3. Do not overload the sieve

Excessive material can reduce sifting efficiency and cause blockage.

4. Do not use excessive force

Forcing material through the sieve can damage the mesh and may alter the material characteristics.

5. Prevent cross-contamination

Ensure proper cleaning and line clearance before starting the next material/product.

6. Control powder dust

Powder handling can generate dust. Follow the site’s engineering controls, PPE requirements, and dust-control procedures.

7. Avoid mix-ups

Keep the sifted and retained materials clearly identified and separated.

8. Check the sieve after operation

Inspect the sieve after use to ensure that the mesh has not been damaged during processing.

9. Record the activity

Important processing activities should be documented according to GMP requirements.

10. Do not ignore abnormal observations

If the sieve suddenly becomes blocked, damaged, or produces an unusual amount of retained material, do not simply continue the operation. Inform the responsible person and follow the applicable procedure.

What Happens If the Wrong Sieve Is Used?

Using an incorrect sieve can affect the downstream process.

Possible consequences include:

Incorrect particle-size distribution
Poor powder flow
Changes in blending behaviour
Variation in granule size
Compression problems
Increased fines
Potential weight variation
Unexplained process variation

The actual impact depends on the material and process.

This is why sieve selection should be controlled through the approved manufacturing process rather than left to operator judgement.

GMP Points to Remember

A good pharmaceutical sifting process should provide control over:

Correct material → Correct sieve → Clean equipment → Intact mesh → Controlled operation → Proper collection → Documentation

From a GMP perspective, the process should be clearly defined and controlled so that it consistently produces the intended result. WHO describes GMP as requiring production and control processes to be clearly defined, validated where appropriate, reviewed, and documented. Pharmaceutical sifting is performed as part of a controlled manufacturing process. For general requirements related to pharmaceutical manufacturing and GMP, refer to the WHO Good Manufacturing Practices (GMP) Guidelines.

Common Mistakes During Pharmaceutical Sifting

Some practical mistakes that can create problems are:

Selecting the sieve based only on habit
Using an unverified sieve
Not checking mesh integrity
Using a dirty sieve
Mixing material from different batches
Overloading the sieve
Forcing lumps through the mesh
Not recording retained material
Ignoring unexplained quantity differences
Keeping sifted material in an unidentified container
Using the same sieve without proper cleaning between products

These may look like small mistakes, but in a GMP environment even a simple sifting operation needs proper control.

FAQ

What is sifting in pharma?

Sifting is the process of passing pharmaceutical powders or granules through a specified sieve to remove oversized particles or lumps and obtain the required particle-size characteristics.

Which sieve is commonly used in pharmaceutical manufacturing?

There is no single standard sieve for all pharmaceutical products. Common mesh sizes include 20, 30, 40, 60, 80 and 100 mesh, but the actual sieve must be selected according to the approved product/process requirement.

What is the difference between 40 mesh and 60 mesh?

A 60-mesh sieve generally has smaller openings than a 40-mesh sieve. Therefore, it provides finer screening. Exact aperture values should be confirmed against the applicable sieve standard.

Why is sifting done before blending?

Sifting can help remove lumps and oversized particles and provide more consistent material for the blending operation.

Can a damaged sieve be used?

No. A sieve with damaged, broken, or otherwise unacceptable mesh should be removed from use and handled according to the site’s procedure.

Is sifting the same as milling?

No. Sifting separates particles according to size. Milling is a size-reduction operation that mechanically reduces particle size.

What should be done with material retained on the sieve?

It depends on the approved process. The retained material may be collected for further processing, milling, investigation, rejection, or disposal. It should not be handled based on operator assumption.

Conclusion

Sifting is a basic pharmaceutical manufacturing operation, but it should not be treated as a casual activity.

The most important controls are:

Correct sieve + intact mesh + clean equipment + controlled sifting + proper material identification + complete documentation.

Most importantly, there is no universal “best sieve size” for pharmaceutical manufacturing. The correct sieve depends on the material, particle-size requirement, manufacturing stage, and approved process.

That approach keeps the operation practical while maintaining GMP control.

Saurabh Saini

Saurabh Saini is a pharmaceutical warehouse professional with over 3 years of hands-on experience in GMP-regulated manufacturing. He currently works as a Junior Officer – Warehouse at Abbott Healthcare and previously served as an Assistant Officer at Mankind Pharma. His expertise includes Raw Material Receipt, Raw Material Dispensing, Warehouse Operations, Inventory Management, GMP documentation, and SOP implementation. Through Pharma GMP Guide, he shares practical GMP knowledge, SOPs, regulatory guidance, and pharmaceutical best practices to help students and industry professionals.