Should Mixing Speed and Mixing Time Be Recorded in My Candle Production SOP Just Like Temperature and Fragrance Percentage?

Why mixing belongs on the SOP next to temperature

Most makers record two things religiously: the fragrance percentage and the temperature at which the oil went in. Both matter. But on a 1 kg test, mixing is almost invisible. You stir a small jug with a bamboo stick, the oil disappears into the wax within seconds, and nothing about the stirring seems worth writing down. At 20 kg that changes. The same oil now has to travel through a much larger, deeper mass of wax, and how you move that wax decides whether candle 1 and candle 100 carry the same load.

So the short answer is yes. Mixing method, speed and time should sit on the production SOP with the same status as temperature and fragrance percentage. The reason is not paperwork. It is that mixing is a process variable that changes finished performance, and any variable that can change the candle has to be fixed, recorded and checked, or it will drift from batch to batch without anyone noticing.

There is a second reason that makers often miss. When a batch fails, the first question is always what was different? If the batch record shows the same oil lot, the same wax, the same temperature and the same load as the last good batch, but has a blank where mixing should be, you have no way to rule mixing in or out. You end up blaming the fragrance oil, raising the load, and paying for more oil to fix a distribution problem that more oil will not fix.

What “mixing speed” means when you stir by hand

A mechanical mixer has a dial, so speed is easy to log. Most small and mid-size makers do not use one. CSI does not sell mechanical mixers either, and you do not need one to write a useful mixing record. For hand stirring, speed becomes a description of the motion rather than an rpm figure. What you are trying to capture is enough detail that a different person on a different day would move the wax the same way.

For hand mixing, the useful fields are: the tool (a long stainless paddle, a spatula, a bamboo stirring stick for small pitchers), the pattern (full-depth figure-of-eight, scraping the base and walls, lifting from the bottom), an approximate pace such as strokes per minute counted over a short interval, the total time from the moment the last of the oil went in, and who did it. For a mixer, record the model, the impeller or paddle type, its height in the vessel, the speed setting and the time.

Record what actually happened, not what the SOP says should have happened. A record that always reads “10 minutes” because that is the target is worse than no record, because it hides the day someone stopped after four.

Worked example: what a blank mixing field cost

Take a maker producing 200 g container candles in CSI 464 soy flakes with Lavender at 8% of total candle weight. A 20 kg scented batch is 18.4 kg of wax plus 1.6 kg of oil, enough for 100 candles before losses, or 95 after a 5% planning allowance.

The material cost of that batch, using CSI's live prices, is easy to work out. CSI 464 costs ₹5,074.00 for 10 kg, which is ₹507.40 per kg at every pack size, so 18.4 kg × ₹507.40 = ₹9,336.16. For 1.6 kg of Lavender, the cheapest pack combination is one 1 kg pack at ₹5,221.00, one 500 g pack at ₹2,620.00 and one 100 g pack at ₹540.00, which totals ₹8,381.00. Wax and oil together come to ₹9,336.16 + ₹8,381.00 = ₹17,717.16, before wicks, jars, labour and packaging.

Now suppose two batches were made a week apart. The first was excellent. The second produced candles whose cold throw varied noticeably from the start of the pour to the end. The batch sheets show identical wax, identical oil lot, identical load and a similar addition temperature. The mixing line on both sheets is empty. One operator remembers stirring “for a while”; the other thinks it was “the usual”.

Without a mixing record, there are only two expensive options: accept the variation or remake the batch with guesses. With a record, the investigation takes an afternoon. If the good batch shows ten minutes of full-depth stirring and the poor one shows four minutes of surface stirring, you have your lead, and you can confirm it with a controlled repeat rather than another ₹17,717.16 gamble.

How to set the mixing numbers you will write down

A recorded number is only useful if it was chosen for a reason. Do not copy your 1 kg stirring time and call it a specification. CSI's only published mixing instruction is for Eco Soy CSI 400, which says to add fragrance at 80–90°C and stir for 2 minutes. That is stated for that wax; it is not a rule for a 20 kg batch.

Instead, establish your numbers with a short validation, then write them into the SOP with a note saying how they were set.

Putting it into the SOP without making it unusable

An SOP that runs to four pages will not be read at the melter. Keep the mixing section to a few lines: the method, the minimum time, the check, and the action if the check fails. Then keep the fuller justification, including the validation results, in a separate file that you revisit when something changes.

Things that should trigger a re-check of the mixing specification include: a larger or different melter, a change in batch size, a new fragrance with a very different feel (thicker, sweeter, heavier), a change of wax, a new operator, and a switch from hand stirring to a mixer or back. Each of those can change how well the same written method distributes the oil.

Keep the thermometer reading and the mixing record on the same line of the sheet. Temperature and mixing interact. Wax that has cooled a few degrees while you stirred is thicker, and thicker wax resists being moved. If the SOP records a single temperature at addition and nothing afterwards, add a second reading at the end of mixing. The melter's display is a guide only, because the product page states a ±10°C deviation, so use the pen thermometer for the recorded figure.

Finally, keep safety on the sheet. Add oil below its published flashpoint, never with the melter at its maximum setting, and keep hands and sleeves clear of any rotating shaft if you do use a mixer. Large melters hold a lot of hot wax and draw significant power, so check the socket and wiring are rated for the load.

If you want help deciding which of your current records to extend first, send a photo of a recent batch sheet to CSI on WhatsApp at +91 7397976926 and we will point out the gaps.

Where this page fits

CSI already has guides that cover parts of this question. This page covers the failure investigation for the question above; these go deeper on the rest:

Three things to buy for this job

Frequently asked questions