The checks before a sample leaves
A sample goes to a laboratory only when the bench work is finished and documented. The first check is that the formula adds to 100.00%, with every line in grams and the water line closing the total. The second is that the preservative is at the supplier's stated dose and inside the legal ceiling, with the actual mass and the delivered percentage recorded. The third is that the pH is inside the target and has been rechecked after 24 hours, because a pH that drifts overnight is a different product by the time it reaches a client. The fourth is that there is no split, graininess or oil ring after the heat screen. The fifth is that the sample is packed in the final jar, with the final lid and the final fill mass, because a lab result on a different pack is a result for a different product. The sixth is that the batch record is complete.
If any one of those six fails, the sample is not ready. A formula that sums to 100 but has the preservative below the supplier dose will fail a challenge test, and sending it wastes the test and the sample. A pH that was measured once and not rechecked may be outside the target by the next morning, and a stability trial started on that sample is a trial of the wrong product. A split after heat is a formulation fault that the lab cannot fix, and a record with a missing lot number cannot be linked to the raw materials that were used.
The order of the checks matters only in that the cheap ones come first. The formula sum and the record review cost nothing. The pH recheck costs a day and a few grams of sample. The heat screen costs a few days. The lab tests cost money and time, and they should be the last step, not the first. A maker who sends a sample to find out whether the formula adds to 100 is paying a laboratory to do arithmetic that belongs on the batch card. Spend the cheap checks first, and let the laboratory answer the questions that only a laboratory can answer, with a sample that is already known to be well made.
Write the checks on a release sheet with a date, a result and an initial for each. The sheet stays with the record. When the lab report comes back, the release sheet shows what state the sample was in when it was sent, which matters if the result is borderline. A sample that was already changing at the time it was packed cannot be rescued by a good report, and a sample that was clean and stable at packing gives a result that can be interpreted. Sign the release sheet, date it, and file it with the record; a check that was done but not written down is a check that cannot be shown.
- 1. Confirm the formula sums to 100.00% in grams.
- 2. Confirm the preservative is at the supplier dose and under the ceiling.
- 3. Recheck the pH after 24 hours and record it with temperature.
- 4. Run the heat screen and confirm there is no split or grain.
- 5. Pack the sample in the final jar with the final lid.
- 6. Complete the batch record, including lots and actual masses.
- 7. Fill in the release sheet with a date, result and initial.
- 8. Only then book the laboratory tests.
Bench example
A maker has a 300 g batch of face cream ready for a laboratory. The release sheet is checked line by line. The formula sums to 100.00%, and the water line is 231.30 g, which matches the batch mass minus the other lines. The preservative is at 0.80%, inside the supplier's range of 0.50 to 1.00%, and the actual mass is 2.41 g against a target of 2.40 g. The pH was 5.38 at combine and 5.36 after 24 hours, both at 25 degrees Celsius. The heat screen at 45 degrees for four weeks shows no split, no grain and no colour change. The sample is packed in two 50 g final jars with the final lids, labelled with the batch code, the date and the tests requested. The record includes the raw material lots and the deviation note for the 0.01 g overshoot. The lab is booked for a total plate count, a yeast and mold count, and a challenge test, and the release sheet is signed the same day. The release sheet is the last page of the record, and it is the page that says the sample was fit to send, not merely available to send.
Caution: Six checks are not a menu. If one fails, the sample stays on the bench; a laboratory cannot test a formula problem out of a jar.
The three tests and what they mean
The total plate count estimates the general bacterial load in the sample at the time of test. A low count means the batch was made cleanly and the preservative is holding at that moment. A high count means the batch, the water, the jars or the handling introduced organisms, and the product should not be sold. The count is a snapshot, not a prediction, and a good result on one batch does not clear a changed supplier, a changed formula or a changed pack. The test method and the acceptance limit come from the laboratory and the applicable rules, not from this book.
The yeast and mold count looks for fungal contamination, which a general plate count may not show well. Mould can grow slowly and appear weeks after filling, especially in a product with high water activity and a preservative system that is strong against bacteria but weak against fungi. A yeast and mold result above the laboratory's limit is a stop signal for the batch, even if the plate count looked acceptable. The two tests are read together, because a product can pass one and fail the other. Read the counts with the pH and the water activity, because those three numbers together describe the environment the organisms had to survive.
The challenge test is the proof that the preservative system holds. The laboratory inoculates the product with a defined mix of organisms, then measures how well the system reduces them over a set period. A pass means the preservative can cope with a reasonable microbial challenge in that formula and that pack. A fail means the system is underdosed, incompatible with another ingredient, or defeated by the pH or the packaging. A challenge test is not a guarantee for every batch; it is evidence that the system works when the formula and the process are followed. If the challenge test fails, the answer is a formulation change, not a larger dose of the same preservative added at the bench without re-testing.
Stability can run in parallel with the microbial work, and it does not replace it. A stable product can still be contaminated, and a clean product can still separate. The lab report is one input to a release decision, not the decision itself. A pass on one batch does not clear a formula change, a raw material change, a new pack or a new supplier. When any of those change, the questions start again, even if the old report was good. Write the scope of each report on the release sheet, so nobody later assumes it covered a lot or a pack that it never saw.
- 1. Ask the laboratory which tests it recommends for the product type.
- 2. Send enough sample for the test and a repeat.
- 3. Request a total plate count for the general bacterial load.
- 4. Request a yeast and mold count for the fungal load.
- 5. Request a challenge test for the preservative system.
- 6. Run stability in parallel, not instead of the microbial work.
- 7. Read the report against the laboratory's stated limits.
- 8. Treat a pass on one batch as evidence, not as a permanent clearance.
Bench example
A salon sends two samples from the same 300 g batch. The first is tested for a total plate count and a yeast and mold count, and both are reported below the laboratory's limit. The second is put through a challenge test, and the report says the preservative reduces the test organisms as required over the test period. The salon reads the report with the batch record: the preservative was at 0.80%, the pH was 5.36, and the sample was in the final jar. The batch is released for a limited trial. Six months later the supplier of the fragrance changes the carrier, and the salon wants to use the new lot. The old report does not cover the new material, so a new sample is made and sent for the same tests. The old report is kept, but it is not used to clear the new batch, because the formula's inputs changed. The release sheet for the second batch records the new lot numbers and the new date. The second release sheet notes the new fragrance lot and the new test date, and the old report is filed as history rather than as current evidence.
Caution: A plate count, a yeast and mold count and a challenge test answer different questions. Do not treat one passing result as though it covered the other two.
Packing and sending a sample
Packing a sample for a laboratory is part of the test. Use a clean, leak-proof container: a screw-cap jar or a bottle with a seal, not a snap-lid pot that can open in transit. Fill enough for the test and a repeat, and ask the laboratory for the volume before you fill. Label the outside with the batch code, the date, the product name and your contact, and put the same information on a label inside the outer bag in case the outer label is damaged. Keep the sample cool in transit and do not leave it in a hot car or on a sunny loading dock.
Send the batch record, or a copy of the relevant page, with the sample. The laboratory needs to know what it is testing, the preservative and its dose, the pH, and the pack. If the sample arrives without that information, the laboratory may test it correctly and still leave you unable to interpret the result. Ask for a written report rather than a verbal pass, and check that the report names the sample, the batch code, the tests and the limits. Do not invent an accreditation number or a method number, and do not copy one from another report. Ask the laboratory what it needs in writing, and keep that reply with the record, so the sample and the request are documented together.
Keep a retention sample from the same batch, in the same pack, stored the same way. If the laboratory result is unexpected, the retention sample is what allows a repeat test or an investigation. Store it with the record and the release sheet, and write the discard date on the jar. Do not open the retention sample to smell it or to show a client; once it is opened it is no longer a retention sample. If a client asks to see the product, use a separate jar from the trial stock, not the retained one. Write the retention sample's location on the record, because a sample that cannot be found is the same as no sample when a question arrives.
Keep the courier receipt and the laboratory's acknowledgement with the record. If a sample is lost or delayed, the receipt is how the chain is traced. Do not send a sample late on a Friday without checking the laboratory's receiving hours, because a sample that sits in a depot over a weekend is not the sample you packed. A laboratory result is only as good as the sample that arrived, and the sample is your responsibility until it is received. If the laboratory reports a problem with the sample on arrival, write that down too, because a result from a compromised sample is not a result.
- 1. Ask the laboratory for the sample volume and the container type.
- 2. Use a clean, leak-proof jar or bottle with a seal.
- 3. Label the outside with batch code, date, product and contact.
- 4. Add a second label inside the outer bag.
- 5. Keep the sample cool and out of direct sun in transit.
- 6. Send the batch record or the relevant page with the sample.
- 7. Keep the courier receipt and the laboratory's acknowledgement.
- 8. Store a retention sample from the same batch with a discard date.
Bench example
A maker packs two 100 mL samples of a toner for a laboratory. The jars are new, screw-capped and sealed with tape, and each is labelled with the batch code, the date, the product name and the salon's phone number. A second label with the same details goes inside the outer bag. The batch record page is printed and placed in a plastic sleeve, with the preservative, the pH and the pack type highlighted. The samples are packed with a cool pack in an insulated box, and the courier is booked for a Monday morning so the box does not sit in a depot over a weekend. The receipt is kept, and the laboratory acknowledges receipt by email the same day. A retention jar from the same batch stays in the cupboard with a discard date written on the lid. When the report arrives three weeks later, the batch code on the report matches the code on the record, the release sheet and the retention jar, and the result can be read against the sample that was actually sent. The evidence file for that batch is complete: release sheet, courier receipt, acknowledgement, report and retention jar in one place.
Caution: Do not open a retention sample to check the smell. Once the seal is broken it is no longer evidence, and a repeat test needs an untouched jar.
This is a Nandu Nai textbook. It is a private brand book, not a government licence, and it does not give the right to give medical treatment.