Cold process soap scales by weight, and has to: the lye is set by the oils, so every batch is weighed, never measured by volume, and a recipe change goes back through a lye calculator. Mix in batches sized to your pot, pour into loaf molds, cut, and cure the bars four to six weeks, during which they lose about a tenth of their weight as water. Done this way, a soap maker that made 24 bars at a time makes about 375 in a day, and the cost of a bar falls from $3.75 to $1.36. Below is the recipe at three sizes, the steps, the cure loss, what a bar costs at each size, and a free scaling calculator.
The short version
- Write oils, lye, water and fragrance as percentages, from a lye calculator.
- Weigh everything; lye is never measured by volume.
- Mix in batches sized to the pot, to a light trace.
- Pour into loaf molds, cut after a day or two.
- Cure four to six weeks; bars lose about a tenth of their weight.
- Gloves and goggles every batch; lye into water, never water into lye.
- TaroStack keeps the recipe by weight, takes each batch's ingredients off stock and checks its yield. More below.
The recipe, by percentage
Cedar Hollow Soap Co., the made-up soap maker in Asheville, North Carolina, I use in these examples, made 24 bars at a time until a gift shop asked for a standing order of three dozen a week on top of its markets. The recipe, weighed:
| Ingredient | % of the mix | Kitchen batch, 7.7 lb | One batch, 40 lb | The run, 120 lb | Cost a lb, bought in bulk |
|---|---|---|---|---|---|
| Olive oil | 35% | 2.69 lb | 14.0 lb | 42.0 lb | $2.50 |
| Coconut oil | 22% | 1.69 lb | 8.80 lb | 26.4 lb | $1.80 |
| Water, distilled | 18.6% | 1.43 lb | 7.44 lb | 22.3 lb | $0.00 |
| Shea butter | 10% | 0.77 lb | 4.00 lb | 12.0 lb | $4.50 |
| Sodium hydroxide (lye) | 9.9% | 0.76 lb | 3.96 lb | 11.9 lb | $2.00 |
| Castor oil | 3% | 0.23 lb | 1.20 lb | 3.60 lb | $3.00 |
| Fragrance or essential oil | 1.5% | 0.12 lb | 0.60 lb | 1.80 lb | $18.00 |
| The whole mix | 100% | 7.7 lb | 40 lb | 120 lb |
The 120 pounds cost $273.48 in ingredients; the olive and coconut oils are most of the weight and the cost. The lye is set for a 5% superfat from these oils, so swapping one oil for another means running the calculator again. Pricing a bar is in how to price soap.
The steps, at 120 pounds
- Mix the lye solution. Lye into distilled water by weight, never the reverse, in a ventilated space, with gloves and goggles; cooled.
- Melt and weigh the oils. Coconut and shea melted, then the liquid oils, all by weight.
- Blend to trace. Lye solution into the oils, stick-blended to a light trace, fragrance stirred in, about 40 pounds a batch.
- Pour into loaf molds. 15 pounds a mold, insulated if the recipe calls for it.
- Cut. After a day or two, into bars of one width on a cutter.
- Cure. Four to six weeks on racks with air around each bar; weigh a few bars at the start and the end.
- Wrap and label. Every bar labeled with the batch's lot and what's in it.
The run takes about 8 hours of labor across mixing day and cutting day.
What a bar costs at each size
| Per bar | Kitchen batch, 7.7 lb | Bulk run, 120 lb |
|---|---|---|
| Ingredients | $1.73 (grocery prices) | $0.73 (bought in bulk) |
| Packaging | $0.35 | $0.20 |
| Labor at $20 an hour | $1.67 (5 min a bar) | $0.43 (1.3 min a bar) |
| Cost of a bar | $3.75 | $1.36 |
Oils by the 35-pound jug and lye by the 50-pound bag cut the ingredients by more than half, and the labor falls from 5 minutes a bar to about 1.3. Margins are in soap business profit margin, and the year in soap business plan.
Soap or cosmetic
A bar made of fats and lye, sold only as soap, is regulated as soap; call it moisturizing or say it treats a skin condition and it becomes a cosmetic, or a drug, with FDA's labeling rules. The difference is in cosmetic labeling requirements.
Get the calculator
Download the soap scaling calculator. Two sheets: scale the recipe, where you type each ingredient's percentage and cost a pound and the raw mix you want, and each ingredient's weight for the run fills in, with the batches, loaf molds, what comes out after the cure loss, the bars it fills and the cost of each bar; and weigh the loss, where what went in and came out over a few batches gives your average cure loss. It's an ordinary Excel file with no macros, and it works in Google Sheets, LibreOffice and Numbers.
Where this stops working
Eight soaps, a batch every week, oils from two suppliers, and bars curing on racks from six different weeks. A sheet can say how much olive oil a run needs, but not which bars are ready to sell, which shea butter went into which batch, or whether the cure loss crept up.
How TaroStack does it
TaroStack keeps the recipe by weight, takes each batch's ingredients off stock and checks its yield.
The recipe in the units you use. A recipe holds each ingredient by weight, with oils bought by the 35-pound jug and used by the pound, and the cost of every bar comes from what you paid. "What could I make right now" says how many runs the oils, lye and fragrance on the shelf allow.
Each run a batch. A run takes its ingredients off stock, records the lots of oils and fragrance it used, and gets a lot of its own for the bars, with how much came out good, how much was rejected and the labor minutes.
Yield checked from history. From your own batch history, TaroStack says whether a recipe yields what it claims and which ingredient's quantity is off, so a cure loss that creeps up shows in the numbers. A loaf that seized in the mold is an adjustment with its reason, spoiled, and shows in the waste report.
| The job | Spreadsheet | In TaroStack |
|---|---|---|
| Ingredients for Monday's run | Multiply, then check the shelf | What could I make right now |
| Which shea butter went into a run | Not written down | Lots recorded on the batch |
| The real cure loss | Weighed now and then | Good and rejected on every batch |
| A loaf that seized | Thrown out, forgotten | Adjustment with a reason |
Recipes, batches, lots and yield are on every plan, from $49 a month. The first 30 days are free, with no credit card. If you'd like a hand setting up, ask, and we'll do it with you.