What Is a Retain Sample, and Why Keep One?
A customer says the product they bought six months ago "has changed its smell". Are they right? Did they store it wrongly, was it a different lot, did the formula change? The only way to answer that question is to have a sample from the batch of six months ago in your hands. That sample is the retain sample.
A retain sample system makes three things possible: assessing a complaint objectively, seeing the difference between lots, and tracking shelf life in real time. For cosmetics manufacturers it is part of good manufacturing practice; for fragrance oil producers and sellers it is just as necessary.
The system holds two distinct kinds of sample: the raw material retain (from every incoming fragrance oil and raw material lot) and the product retain (from every finished product batch produced). Both follow the same logic and are kept on separate shelves.
How Much, for How Long, and How Is It Stored?
The answers to these three questions vary by material type; the table below is a practical starting point.
| Sample type | Quantity | Retention period | Conditions |
|---|---|---|---|
| Fragrance oil / aroma chemical lot | 20–30 g (enough for two full evaluations) | Shelf life + 1 year | Amber glass, filled to the top, 15–20°C, dark |
| Natural oil lot | 20–30 g | Shelf life + 1 year | Same; a cool cabinet is preferred for citrus and conifers |
| Solvent, alcohol | 50 ml | 1 year | Amber glass, closed |
| Finished product (perfume, room fragrance) | 1 retail unit, preferably 2 | Shelf life + 1 year | In retail packaging, in its original box, dark, room temperature |
| Finished product (candle, soap, cream) | 1 retail unit | Shelf life + 1 year | In retail packaging; away from temperature fluctuations |
The quantity rule: a retain sample must be enough for a full evaluation (odour, appearance, density) twice if needed. A sample used up in one evaluation is useless at the second complaint.
The storage condition is the one on the product label, not a better one. If you keep the retain sample in the fridge, it can no longer be compared with the product on the customer's shelf. The aim is not to protect the sample but for it to represent the real ageing of the product.
Setting Up the System: Step by Step
A retain sample system consists of a shelf, a logbook and a habit. Setting it up takes a day; running it takes five minutes per lot and per batch.
- Set aside the shelf
A lockable cabinet, or at least a separate one; dark, cool, away from the production area. Raw material and product retains on separate shelves.
- Define the numbering rule
Raw material retain: raw material code + supplier lot + date of receipt. Product retain: product code + batch number. The number is written on the label and in the logbook in the same format.
- Take a sample from every incoming lot and every batch
20–30 g for every lot that passes incoming inspection, 1–2 retail units from the filling of every production batch. The sample is taken from the middle of the batch, not the beginning.
- Label
Number, product name, lot/batch, date, end of retention period, "RETAIN – not for use". Use a fade-proof marker; it will be read for five years.
- Record in the logbook
Number, what, when, where it was put, when it is to be disposed of. When an evaluation is done, the date and result are added on the same line.
- Plan periodic smelling
Fragrance oil and product retains are smelled at months 6 and 12, then once a year; appearance is checked and the result goes in the logbook. This is real-time shelf life data.
- Dispose of expired samples
A sample whose retention period has ended is disposed of and the disposal is recorded in the logbook. Samples whose period has not ended are not thrown away just to free up the shelf.
When Is a Retain Sample Opened, and How Is It Evaluated?
A retain sample is opened in three situations: a customer complaint, a lot comparison and a periodic check. In every case the method is the same: the retain and the sample under question are smelled at the same dilution, on the same blotter, at the same time and the differences are recorded numerically.
For a complaint: ask the customer to return the product. Three samples side by side: the retain, the customer's product, and a product from the same batch on your shelf. If the retain and the shelf product are the same and the customer's differs, the problem is in storage conditions; if all three differ, the problem is in the batch or in shelf life; if all are the same, the complaint is about perception or expectation. Each outcome calls for a different answer, and without the retain none of them can be known.
For a lot comparison: the new lot alongside the approved retain; if there is a difference it is confirmed with a triangle test, and density and refractive index are measured. Does the accepted new lot become the retain for the next comparison? No; the retain remains the approved reference lot. Changing the reference is a separate, written decision.
For a periodic check: the sample is opened, smelled, its appearance checked, and closed immediately. Every opening ages the sample a little; this is why keeping two samples and storing one as "never opened" is good practice.
Frequently Asked Questions
The most common questions about the retain sample system.
Is a retain sample a legal requirement?
Should I set aside a sample per lot or per order?
Isn't it better to keep the sample in the fridge?
How much space is needed?
If the odour of the retain sample changes over time, does it stop being a reference?
Is an opened product enough as a finished product retain?
Who should do the periodic smelling?
How is the retain system linked to the batch record system?
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