I Have Half a Drum of an Older Fragrance Batch and a New Drum Has Arrived — Should I Mix Them Together or Transition Between Batches Separately?

Why topping up is tempting, and wrong

A half-used drum takes up the same space as a full one. Pouring it into the new drum, or the new oil into the old one, seems like the obvious way to tidy the store and avoid working from two containers. It is also the most common way workshops lose track of their fragrance batches.

Three things go wrong at once. First, traceability goes. Every candle made from the combined drum now contains an unknown ratio of two batches, and you cannot say which candles contain how much of which. Second, any change in the older oil travels into the new stock. A container that has been opened repeatedly and is half empty has had more air above the oil for longer, and some fragrance materials change with time, air, light and heat. Third, the transfer itself is a risk: decanting a flammable liquid between large containers invites spills, splashes and contamination from a funnel or jug that was used for something else.

There is a fourth, quieter problem. Once the drums are combined, you can never again compare the old batch with the new one, because neither exists on its own any more. If customers later say the fragrance has changed, the one test that could settle the question has been made impossible.

None of this means the old oil is bad. It means the two batches should meet only in a measured, recorded way, if at all.

Use the old drum first, after checking it

First in, first out is the right principle for fragrance oil, as long as the older material still performs. So before you commit the remainder to customer stock, confirm that it has not drifted. Compare the old oil on a smelling strip against a retained reference candle or a sealed reference sample from when the drum was approved. Look at its colour in a clean beaker against a white card. If anything seems different, make a small comparison candle before using it.

Look at how much production the remainder supports. Suppose your drum held 25 kg and roughly half remains, about 12.5 kg. At 8% of total candle weight, each 200 g candle takes 16 g of oil, so 12.5 kg supports about 781 candles, or around 742 after a 5% wastage allowance. That is weeks of work for many workshops, which is plenty of time to validate the new drum properly rather than in a hurry.

If the old oil has drifted

Sometimes the check shows the older oil is no longer quite what it was: flatter on the strip, darker in the beaker, or weaker in a comparison candle. Do not try to rescue it by blending in fresh oil or by raising the load. Take it off customer production, label it clearly as on hold, and compare it against the new drum once that has been validated. If the new drum matches your reference and the old one does not, the old remainder has aged or been affected by storage. Decide separately whether it has any use, such as internal testing, and record that decision, so it never drifts back into stock by accident.

Validate the new drum in parallel

While the old drum is being used, test the new one. The aim is to have it approved before the old one runs out, so there is no pressure to switch to an untested oil because production cannot wait.

For CSI oils, ask on WhatsApp (+91 7397976926) for IFRA and MSDS documents if you do not have them on file, and ask what batch information CSI can share for the new delivery. Record only what they confirm.

Plan the changeover point

Choose where the switch happens before you reach it. The best point is an order or SKU boundary: finish the corporate order on the old oil, then start general stock on the new. If the old drum will not quite cover the current order, it is often better to start that order on the new drum from the beginning, so one customer's candles all share one oil batch.

The two handover candles, one from the last old-drum batch and one from the first new-drum batch, are your evidence that the change was invisible to customers. Keep them with the batch records.

Make the plan visible on the floor. A simple tag on each drum, IN USE on the old one and NEXT on the new, with the planned changeover batch written on both, stops a busy team member from opening the new drum early because it was closer to hand.

If the remainder is too small

If the old drum ends with a small amount that will not make a full batch, you have two sound options. Make a short batch from it on its own, or combine it with new oil inside a single production batch, weighed and recorded: for example, 300 g from the old drum and 500 g from the new in a 10 kg batch at 8%. The combination happens in the batch, never in the drum, and the batch sheet shows both references and both weights.

Closing out the old drum

When the old drum is empty, close it on your raw-material record with the date and the batch code of its last use. Do not refill it with new oil. If you reuse drums, clean and dry them thoroughly first, remove or cover the old labels, and relabel clearly, because a cleaned drum still carrying an old label is a trap for someone later.

Store fragrance drums tightly closed, upright, in a cool, dry, dark place away from heat and ignition sources. Some oils have stated flashpoints below 100°C, such as Roasted Coconut at 93°C and Gardenia at 98°C, so storage near a hot melter is never appropriate for any of them.

Where this page fits

CSI already has guides that cover parts of this question. This page takes the production-floor angle; these go deeper on the rest:

Three things to buy for this job

Frequently asked questions