Home canning books say not to double a jam recipe, and at the stove they're right: a big pot cooks slowly, and jam cooked too long tastes of caramel and sets badly. A preserves maker gets around it with a steam kettle, which boils a big batch fast, and by cooking to a number instead of a time: 65% soluble solids, read on a refractometer, the same figure the standard for jam uses. Done this way, a preserves maker that cooked 8 jars at a time makes 200 in a day, and the cost of a 9-ounce jar falls from $7.28 to $2.85. Below is the recipe at three sizes, the steps, the cook loss, what a jar costs at each size, and a free scaling calculator.
The short version
- Write fruit, sugar, acid and pectin as percentages.
- Cook in a steam kettle that boils a big batch fast.
- Cook to 65% soluble solids on a refractometer, not to a time.
- Fill hot, cap and check every seal.
- About a fifth of the weight cooks off; cost the jar from what comes out.
- Jam is an acid food, not an acidified one.
- TaroStack keeps the recipe by weight, takes each batch's ingredients off stock and checks its yield. More below.
The recipe, by percentage
Old Mission Preserves, the made-up preserves maker in Traverse City, Michigan, I use in these examples, cooked tart cherry preserves 8 jars at a time before moving to a steam kettle and batches of 200. The recipe, weighed:
| Ingredient | % of the mix | Kitchen batch, 6 lb | One batch, 50 lb | The run, 145 lb | Cost a lb, bought in bulk |
|---|---|---|---|---|---|
| Tart cherries, pitted | 55% | 3.30 lb | 27.5 lb | 79.8 lb | $2.20 |
| Sugar | 40% | 2.40 lb | 20.0 lb | 58.0 lb | $0.60 |
| Lemon juice | 4% | 0.24 lb | 2.00 lb | 5.80 lb | $2.50 |
| Pectin | 1% | 0.06 lb | 0.50 lb | 1.45 lb | $12.00 |
| The whole mix | 100% | 6 lb | 50 lb | 145 lb |
The 145 pounds cost $242.15 in ingredients, most of it cherries. Fifty-five parts cherries to forty of sugar is well above the standard's minimum fruit share, so the jar can say "preserves"; how the name works is in jam labeling requirements.
The steps, at 145 pounds
- Weigh the fruit and sugar for each cook. About 50 pounds a cook, cherries first, sugar and lemon juice by percentage.
- Boil fast. In the steam kettle, stirred, at a full rolling boil.
- Cook to the number. Pectin whisked in with some of the sugar, and the batch cooked until the refractometer reads 65%.
- Fill hot. Into hot jars, capped at once, and processed or inverted as the kitchen's written process says.
- Check the seals. Once cool, every lid pulled down; a jar that didn't seal goes to the staff shelf.
- Weigh what comes out. Over three runs, about 22% of the weight cooks off.
- Label with a lot code. Every jar from the run carries the run's lot and date.
A run of three cooks takes one person about 8 hours, pitting aside.
What a jar costs at each size
| Per jar | Kitchen batch, 6 lb | Bulk run, 145 lb |
|---|---|---|
| Ingredients | $2.41 (grocery prices) | $1.20 (bought in bulk) |
| Packaging | $1.20 | $0.85 |
| Labor at $20 an hour | $3.67 (11 min a jar) | $0.80 (2.4 min a jar) |
| Cost of a jar | $7.28 | $2.85 |
Cherries by the 30-pound pail from a farm and sugar by the 50-pound sack halve the ingredients, and the labor falls from 11 minutes a jar to about 2. The jar, lid and label are almost a third of a jar's cost at either size. Pricing the jar is in how to price jam, and handing the cooking to someone else in jam co-packer.
Why jam isn't an acidified food
Fruit jams and preserves are naturally acid and high in sugar, so they're acid foods, outside the acidified food rules that cover salsa and pickles; the difference is in acid food vs acidified food. They still need a safe fill and seal, and a written plan for the kitchen, in jam HACCP plan.
Get the calculator
Download the jam 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 kettle cooks, what comes out after the cook loss, the jars it fills and the cost of each jar; and weigh the loss, where what went in and came out over a few batches gives your average cook loss. It's an ordinary Excel file with no macros, and it works in Google Sheets, LibreOffice and Numbers.
Where this stops working
Cherry, strawberry and a cherry-rhubarb, cooks all summer, cherries from three farms, and a grocer asking about one jar. A sheet can say how much sugar a run needs, but not which farm's cherries went into which jar, or whether the cook loss has 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 cherries bought by the 30-pound pail and used by the pound, and the cost of every jar comes from what you paid. "What could I make right now" says how many runs the cherries, sugar and jars on the shelf allow.
Each run a batch. A run takes its ingredients off stock, records the lots of cherries it used, and gets a lot of its own for the jars, 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 cook loss that creeps up shows in the numbers. A pail of cherries that thawed 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 cherries went into a run | Not written down | Lots recorded on the batch |
| The real cook loss | Weighed now and then | Good and rejected on every batch |
| Cherries that thawed | 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.