Jam and preserves cost: cook-down loss and jars

To cost jam you need three weights: the fruit you bought, the fruit left after preparing it, and the finished jam that comes out of the pan. Between the first and the last you can lose a large part of the weight, which is why working out jars from what went into the pan always gives a cost lower than the real one. The cost per jar is the cost of all the ingredients divided by the jars you actually fill, plus the jar, lid, label, your time and the energy, which matters more in jam than in most products because the boil is long.

Three weights to write down

1. Bought weight: what the receipt from the market says.
2. Prepared weight: what is left after hulling, stoning, peeling and throwing out bruised fruit.
3. Finished weight: the jam, sugar included, when you turn off the heat.

You cost from what you bought, because that is what you paid for. You count yield from what you fill, because that is what you sell. In between sit two losses you have to measure yourself: preparation and cook-down.

Preparation: from bought kilo to usable kilo

If you buy 5 kg of strawberries and after hulling and binning the soft ones you have 4.6 kg, your preparation yield is 4.6 ÷ 5 = 92%. That percentage is yours, and it moves with the quality of each batch and each seller. The guide on yield percentage: as purchased vs usable shows how to measure it, and the yield tool gives you the real cost per usable kilo.

At 92%, strawberries that cost you $3.20 a kilo really cost 3.20 ÷ 0.92 = $3.48 per prepared kilo.

Cook-down: weigh the pan before and after

Jam is made by boiling off water. That makes it the product where the gap between what goes in and what comes out is most obvious. To measure it:

1. Weigh the empty pan and write down the tare.
2. Weigh everything that goes in: prepared fruit, sugar, lemon juice, pectin if you use it.
3. When it reaches setting point, weigh the pan with the jam and subtract the tare.

The difference between in and out is your cook-down loss. It changes with the water in the fruit, the width of the pan, the heat and how firm you like the set. Measure several batches and use the average. The guide on how to measure recipe yield shows how to keep it consistent.

One detail people miss: if one day you boil five minutes longer for a firmer set, you get fewer jars from the same batch. The set is a cost decision too.

From finished batch to jars

From the finished weight you still lose what sticks to the pan and the ladle, the jar you open to taste, and the few grams of overfill you add so no jar comes in under the label. It is the same sum as for sauces; the guide on cost per jar for sauces and chilli pastes goes through it step by step.

Then add per jar the glass, the lid and the label, as in the guide on how to cost packaging and labels, plus your time and the energy, to reach the loaded cost per unit.

Worked example: strawberry jam in 340 g jars

You buy strawberries at the end of the day at the farmers market for a batch of jam.

The three weights:

• Bought: 5 kg of strawberries
• Prepared: 4.6 kg. With the sugar and about 150 g of lemon juice, 4.6 + 3.0 + 0.15 = 7.75 kg goes into the pan
• Finished: you weigh the pan at the end, subtract the tare and get 6.0 kg. You boiled off 7.75 − 6.0 = 1.75 kg, which is 1.75 ÷ 7.75 = 23% of what went in

Jars. About 120 g stays in the pan and on the ladle, so you fill from 5.88 kg. You put 345 g in each jar to be sure of the 340 g on the label.

• 5,880 ÷ 345 = 17.04, so 17 jars. The last 15 g is a taster.

Cost per jar:

• Ingredients: 23.00 ÷ 17 = $1.35
• Jar and lid $0.95 + label $0.20 = $1.15
• Your time: 3 hours to hull, boil, sterilise, fill and label; 3 × $15 = $45; 45 ÷ 17 = $2.65
• Energy for the boil and the sterilising: $3.40; 3.40 ÷ 17 = $0.20
• Total: 1.35 + 1.15 + 2.65 + 0.20 = $5.35 per jar

The going-in mistake. If you divide the 7.75 kg that went into the pan by 340 g, you plan on 22 jars. With 22 jars the cost looked like 23.00 ÷ 22 + 1.15 + 45 ÷ 22 + 3.40 ÷ 22 = $4.40. That is $0.95 a jar off, with five jars in your plan that never existed. Price on $4.40 and every jar you sell leaves you $0.95 less than you think.

One more useful number: your fillable jam costs 23.00 ÷ 5.88 = $3.91 a kilo in ingredients alone. With that you can cost other jar sizes quickly.

What moves the cost of jam

• The fruit price. It is the most expensive ingredient and the one that moves most with the season. Run the sum at the expensive months' price as well; the guide on handling seasonal prices helps you plan for it.
• Preparation yield. A cheap tray of bruised fruit can cost more per prepared kilo than a good one at a higher price. Always compare per prepared kilo.
• The set. More cook-down, fewer jars. If you change the recipe, measure again.
• Time at the stove. Jam needs stirring and watching. Those hours are yours and go into the cost.
• Shelf life. If you sell through shops, the jar has to last its time on the shelf. The guide on shelf-life tests and batch records covers what it costs to check.

With the cost per jar settled, the next step is the price. The guide on how to price a packaged food product takes that number up to the shelf price, through the shop's and the distributor's margins.

Do it with the calculator

In the cost calculator you enter the fruit at the price you paid, the sugar, the jars you actually filled and the cost of the jar and label. It gives you the loaded cost per jar, which is the number you set your price on.