Adjusting recipes to the pack sizes you buy

When a recipe uses only part of a pack, its real cost depends on what happens to the rest. If the leftover goes into the next batch, you can cost by the gram. If it spoils or disappears, the real cost of your batch is the whole pack, whatever the recipe card says. The 85 g of chocolate you take from a 180 g bar costs $1.70 on paper. If the other 95 g gets nibbled, forgotten or used as a snack, those 85 g cost you $3.60.

Two ways to cost an opened pack

By the gram: pack price ÷ pack size × grams used. This is the standard method and the right one when the whole pack ends up in product you sell, sooner or later.

By the whole pack: if every time you make the recipe you open a pack and the rest is lost, the batch carries the whole pack. Put another way, every gram you did use cost more than the label suggests. In the chocolate case, 3.60 ÷ 85 = $0.042 per gram instead of $0.020.

One question decides which to use: does the leftover become sold product before it goes off? Not what should happen. What actually happens in your kitchen.

Which leftovers get used and which get lost

It depends on how long the opened ingredient keeps and how often you cook.

• Keep well: flour, sugar, chocolate wrapped tight, nuts in a sealed tub, spices, oil. The leftover waits for the next batch and the per-gram cost is honest.
• Do not keep: opened cream, fresh soft cheese, herbs, ripe fruit, opened tins of coconut milk. If your next batch is next week, the leftover will not make it.

There is a third case that slips past most people: the small remainder that repeats. The recipe takes 85 g and the bar is 180 g. Two batches use 170 g and leave 10 g, which breaks into crumbs and gets eaten. In practice, each batch costs half a bar, $1.80, not $1.70. Raising the recipe to 90 g costs you nothing extra and gives exactly two batches per bar.

If you can only watch one ingredient, start with the one that is expensive and does not keep. A sugar remainder barely moves your cost. A cream remainder does.

Worked example: brownies with a ganache top

You bake one tray of 16 brownies a week for a café. Each tray uses 85 g of chocolate in the batter and 150 ml of cream in the ganache.

• Everything else (butter, sugar, eggs, flour, cocoa, more chocolate for the ganache): $5.20 per tray.
• Chocolate for the batter: 180 g bar at $3.60, or $0.020 per gram.
• Cream: 300 ml carton at $2.40, or $0.008 per ml. Once opened, it does not last until next week.

What the recipe card says (by the gram):

• Chocolate: 85 × 0.020 = $1.70
• Cream: 150 × 0.008 = $1.20
• Tray: 5.20 + 1.70 + 1.20 = $8.10
• Per brownie: 8.10 ÷ 16 = $0.51

What actually happens: the other 150 ml of cream goes off before next week. The chocolate leftover goes into the next tray, but every second tray leaves a 10 g stub that never gets used, so chocolate really costs half a bar per tray.

• Chocolate: 3.60 ÷ 2 = $1.80
• Cream: the whole carton, $2.40
• Tray: 5.20 + 1.80 + 2.40 = $9.40
• Per brownie: 9.40 ÷ 16 = $0.59

Each tray costs $1.30 more than the card says, 16% more (1.30 ÷ 8.10). And if the open bar tends to disappear between bakes, the tray costs 5.20 + 3.60 + 2.40 = $11.20, or $0.70 a brownie: 38% above the card (3.10 ÷ 8.10). That is a price built on $0.51 for a brownie whose ingredients cost $0.59 to $0.70.

The fix:

• Round the chocolate to 90 g. Two trays per bar exactly: 3.60 ÷ 2 = $1.80 per tray, nothing left over, and 5 g more chocolate in each tray for the same money.
• Bake two trays back to back on the same day. One 300 ml carton covers both ganaches: $1.20 per tray.
• Tray: 5.20 + 1.80 + 1.20 = $8.20. Per brownie: 8.20 ÷ 16 = $0.51.

The card is honest again. The catch is that you now make 32 brownies at once, so this only works if the café takes them or they freeze well.

Four ways to fix it

1. Round the recipe to the pack. If the change is small, adjust the quantity so one pack gives an exact number of batches, like 85 g to 90 g. Test a batch before changing the card.
2. Change the batch size. Making two trays at once uses the whole carton, but only pays if you sell them while they are fresh. How cost per unit moves with batch size is covered in how batch size changes your cost per unit.
3. Plan the leftover. If the spare cream goes into another product that same week (a sauce, a second ganache, whipped cream for a cake order), per-gram costing becomes true. Write it into your plan; do not leave it to luck.
4. Buy a different size. Big packs are cheaper per kilo, but buying in bulk only saves money if you use it all. Sometimes the small pack is cheaper per unit you sell. If no pack size fits, look at substituting the ingredient for one sold in amounts that suit you.

Write it on the card

On your recipe card, next to every ingredient that comes in a pack, write the pack size and what happens to the leftover: "kept" or "lost". If lost, cost the whole pack. That way the cost you price from is the one you pay, not the one you wish you paid.

Check again whenever you change supplier or pack size: a 900 ml tub instead of a 1 litre one changes every number. The guide to recipe costing, yield and waste shows how this adjustment fits with the rest of a recipe's cost.

Do it with the calculator

In the food cost calculator you can enter an ingredient with the amount you use or with the whole pack. Try both and you will see, per unit, what the lost leftover costs you.