Agriculture & Future Food Systems · Article

Yield, by-products and process losses

Reconcile a food-process input with products, remaining fractions, water leaving the boundary and material still in equipment.

Preparation and related reading

Shared Foundations

This article helps you

Close a process mass account with explicit inputs, outputs and inventory.
Distinguish wet-product yield from dry-material recovery.
Explain why a remaining fraction is not automatically waste or a usable ingredient.

Ask where the input went

A processor receives 100 kg of apples but collects only 65 kg of juice. Thirty-five kilograms have not necessarily vanished or been wasted. Material can leave in a pulp fraction, water vapour or another stream, and some can remain inside equipment. A useful account names those destinations.

Define the interval and boundary first: for example one processing run from weighed input to weighed collected streams. Record any added water or ingredients and any material left from a previous run. This article uses a simplified hypothetical separation with no additions, no starting equipment inventory and no chemical conversion.

Close the whole material account

In the hypothetical run, the 100 kg input gives 65 kg juice, 25 kg pulp and 7 kg water vapour leaving the boundary. Another 3 kg remains in equipment at the end. The account closes: 65+25+7+3 = 100 kg. Equipment inventory is a storage term; it is not a collected output and is not automatically lost food.

The figures are stipulated teaching quantities. A real unresolved difference could reflect unmeasured streams, scale error, sampling or changed inventory. First investigate the measurements rather than assigning the difference to one convenient explanation. The shared Measurement Uncertainty record develops how reported quantities can differ from their actual values.

Hypothetical run, with all stated mass destinations
Destination	Mass	Role
Collected juice	65 kg	Selected product stream
Collected pulp	25 kg	Separate remaining fraction
Water vapour leaving	7 kg	Water removed
Final equipment inventory	3 kg	Material still inside
Total accounted material	100 kg	Matches input

Account for all 100 kg

Original hypothetical mass account with a table identifying the other terms. Arrow widths do not encode mass; not all remaining material is food loss.

Read the diagram as text

The hypothetical input is allocated to 65 kg juice, 25 kg pulp, 7 kg water vapour and 3 kg final equipment inventory, with no additions or initial inventory.

Parts

100 kg input: No additions or initial equipment inventory.
65 kg juice: Collected product stream; acceptance is separate.
35 kg other terms: 25 kg pulp + 7 kg vapour + 3 kg inventory.

Connections

100 kg input → 65 kg juice: selected product
100 kg input → 35 kg other terms: remaining account

Give yield its denominator

Wet juice yield by incoming mass is 65/100 = 65%. It describes this product stream and basis. It is not 65% recovery of every constituent, and it does not establish that 65 kg has been accepted for sale. Composition and product specifications remain separate.

Added water can increase a product’s wet mass without increasing its recovered apple material. Comparing processes therefore needs the same input basis, product form and reporting point. State whether a number concerns all collected material, a selected fraction or accepted final food; the word “yield” alone leaves that question unanswered.

Follow dry material separately

Assume the incoming apples contain 20 kg dry material and 80 kg water. The recorded dry material is 8 kg in juice, 10 kg in pulp and 2 kg in final equipment inventory. Those terms sum to 20 kg. Corresponding water masses are 57, 15 and 1 kg, plus 7 kg vapour: 80 kg in total.

Recovery of incoming dry material into juice is 8/20 = 40%. Juice dry-matter content is instead 8/65 ≈ 12.3% by wet mass. These calculations use the same 8 kg numerator but different denominators. Neither result is a protein fraction or a measure of retained vitamins. Constituent-specific recovery needs its own measurements.

Distinguish side streams from food loss

A by-product is a material with another actual use in the defined process context; calling a fraction a by-product does not create a destination or establish suitability. The pulp might be assessed for a food ingredient, another productive use or disposal. Its composition, contamination risks, handling and actual destination determine what is feasible.

Food-loss reporting uses a specified edible-food and supply-chain definition. It is not identical to the mass that did not enter the main product. Intentional removal of water, material stored inside equipment and collected usable fractions need to remain visible in a process account. Record their fate before applying a particular loss framework.

Improve recovery without hiding tradeoffs

A higher main-product yield may require more water, energy, processing or rejected material elsewhere. It can also change texture or dilute composition. Improvement means more suitable output for the intended function within an explicit resource and quality account, rather than maximizing one percentage.

Track several terms together: accepted product, composition, usable remaining fractions, final inventory and utilities. Investigate repeatability across actual runs before predicting performance. The resources branch develops circular use and full-system comparisons; food safety and ingredient functionality determine whether a recovered fraction can responsibly become food.

Worked examples

Find the final inventory

What remains inside after the hypothetical 100 kg input gives 65 kg juice, 25 kg pulp and 7 kg water vapour?

Collected and escaping mass: 65+25+7 = 97 kg.
Final inventory: 100−97 = 3 kg, with the stated zero starting inventory and no additions.
Check closure: 65+25+7+3 = 100 kg.

Three kilograms remain in equipment under the stipulated complete account. A real unexplained difference would require investigation.

Use the two dry-matter denominators

What do 8 kg dry material in 65 kg juice and 20 kg incoming dry material imply?

Recovery into juice: 8/20×100 = 40%.
Juice composition: 8/65×100 ≈ 12.3% dry matter.
Dry material closure: 8+10+2 = 20 kg.

The juice recovers 40% of incoming dry material and contains approximately 12.3% dry matter by wet mass; these are different quantities.

Check your understanding

Does 65% wet juice yield mean 65% dry-material recovery in this example?
Show answer and reasoning
No; the stipulated dry-material recovery is 40%.
Use the 20 kg incoming dry-material denominator, not the 100 kg wet input.
Can the 3 kg remaining in equipment automatically be reported as discarded food?
Show answer and reasoning
No.
Inventory has not yet been collected or assigned a destination; food-loss classification needs its actual fate and chosen definition.
Does a named pulp by-product establish that it is safe to add to food?
Show answer and reasoning
No.
Its identity, specification, hazards, processing and intended use must be assessed; a useful-sounding name is not evidence.

Key ideas

Include outputs, additions and inventory when closing a material account.
Define each yield or recovery denominator and retain moisture basis.
Determine actual destinations and suitable uses before labeling side streams as waste or recovered food.

References

Sources supporting the explanations and examples in this article.

Food and Agriculture Organization of the United Nations3 sources