Agriculture & Future Food Systems · Article

Harvest, ingredients and contaminants

Follow algal biomass through separation and ingredient preparation, keeping composition, product identity and hazards on the correct mass and use basis.

Preparation and related reading

Shared Foundations

This article helps you

Separate dry matter, wet paste and target ingredient recovery.
Explain why species, site and processing affect food-quality assessment.
Calculate a hypothetical constituent amount without turning it into a safety recommendation.

Identify the material and use

A harvested algae lot becomes a food ingredient through a defined process and specification. Macroalgae may be handled as larger pieces; microalgae may arrive as cells suspended in culture liquid. Naming the species, cultivated material, harvest lot and intended use connects those different starting points with the product being assessed.

Whole biomass and an extracted ingredient need different descriptions. A protein fraction, oil or other recovered component is not compositionally identical to the original organism. ETH Zurich’s research summaries illustrate that species and cultivation conditions affect composition and ingredient behavior; a promising laboratory result does not establish a finished food’s performance or safety.

Separate dewatering from recovery

Dewatering removes some liquid from wet material. Ingredient recovery concerns how much of a selected material remains in the chosen product stream. A lower wet mass can arise mainly from water removal, while a high recovery still leaves a wet paste. Record both the material quantity and the denominator.

Consider an invented separation with 1 kg initial dry matter and 90% dry-matter recovery. The retained dry matter is 0.9 kg. If the measured final paste is 10% dry matter by mass, its total wet mass is 0.9/0.10 = 9 kg. Under a two-part dry-matter-and-water account, that paste contains 8.1 kg water. This is not a drying instruction or a complete water balance.

Hypothetical recovery and paste composition
Quantity	Value	Calculation or limit
Initial dry matter	1 kg	Starting material basis
Retained dry matter	0.9 kg	1 × 0.90
Final paste dry-matter fraction	10%	Measured or explicitly assumed
Final wet paste	9 kg	0.9/0.10
Water in final paste	8.1 kg	9 − 0.9; two-part account

Read recovery and composition together

Original hypothetical accounting diagram. The second arrow changes the reporting basis; it does not add biomass or describe a complete water flow. No food-safety result or operating recipe is implied.

Read the diagram as text

One kilogram initial dry matter gives 0.9 kg retained at 90% recovery. A 10% dry-matter fraction then corresponds to 9 kg wet paste containing that retained material.

Parts

1 kg initial dry matter: The starting material quantity for recovery.
0.9 kg retained dry matter: 90% recovery of the initial dry matter.
9 kg wet paste: 10% dry matter: 0.9 kg dry matter plus 8.1 kg water.

Connections

1 kg initial dry matter → 0.9 kg retained dry matter: 90% recovery
0.9 kg retained dry matter → 9 kg wet paste: 10% dry matter

Assess chemical hazards specifically

Seaweed can contain iodine and metals or metalloids, with differences among species, source environments and products. Iodine is an essential nutrient, but that does not make every amount suitable for every use. EFSA’s assessment distinguishes total arsenic from inorganic arsenic: they are different analytical quantities and cannot simply substitute for each other.

The relevant question is which constituents occur in this product, on which analytical basis, and how the product will be used. A dry-basis result must not be attached to an unspecified wet serving. Cleaning or cooking is not a universal way to remove chemical hazards. Product assessment and applicable requirements need evidence beyond a species name or colour.

Keep microbial and physical hazards visible

Growing environment and handling can introduce or affect microbial hazards. Harvest equipment, transport, water contact and later processing belong in the assessment. Physical material such as grit or fragments is another hazard category. A contaminant need not be visible, and a normal smell does not verify microbiological safety.

Controls must be appropriate to the product and process and their effectiveness demonstrated. This is not a home-culturing or preservation recipe. Safe water, equipment hygiene, storage and validated processing are developed in Food Science and Safety; separating cells or removing water does not by itself establish that the resulting ingredient is safe.

Calculate content without setting a dose

Suppose a hypothetical dry product is measured at 20 mg iodine/kg and a calculation uses 5 g of that same product. Convert 5 g to 0.005 kg, then multiply: 20 mg/kg × 0.005 kg = 0.10 mg, or 100 micrograms. This establishes the assumed iodine amount in that portion, not an appropriate intake or a legal limit.

The result depends on the actual analytical value, sample representativeness and matched product basis. A different species, batch, moisture content or processing route can change the value. EFSA’s European assessment also records limits in the occurrence and consumption evidence; an exposure estimate does not automatically describe every consumer or market.

Connect quality with useful output

A useful ingredient needs a known identity, reproducible specification and a function in the intended food. Composition alone does not determine flavour, texture, digestibility or performance in a formulation. Those questions require suitable product tests rather than an assumption that all algal biomass supplies the same nutrition.

Compare resource demands per accepted output or required ingredient function. Include separation, processing, testing, rejected material, water management and energy. The hypothetical 9 kg paste is not 9 kg dry ingredient, and a chemical analysis alone is not a release decision. Actual production evidence joins mass accounting with the assessment of the product people will eat.

Worked examples

Find wet paste from retained dry matter

What paste mass contains 0.9 kg retained dry matter at 10% dry matter by mass?

Retained dry matter is 1 × 0.90 = 0.9 kg.
0.9/0.10 = 9 kg total paste.
9 − 0.9 = 8.1 kg water under the two-part account.

The paste is 9 kg on the stated basis. Its dry-matter recovery is 90%; its water content and suitability as food are separate questions.

Convert an analytical concentration into an amount

What iodine amount follows from the hypothetical 20 mg/kg value and 5 g portion of the same dry product?

5 g = 0.005 kg.
20 × 0.005 = 0.10 mg.
0.10 mg × 1,000 = 100 micrograms.

The calculated amount is 100 micrograms. This example supplies no serving recommendation, safety judgement or legal threshold.

Check your understanding

Does removing 90% of a slurry’s water necessarily recover 90% of its dry matter?
Show answer and reasoning
No.
Water removal and dry-matter recovery concern different quantities and need separate measurements.
Can a total-arsenic result be relabelled as inorganic arsenic?
Show answer and reasoning
No.
The analytical quantities differ. Product-specific hazard assessment needs the relevant measurement.
Can 9 kg of the hypothetical paste be reported as 9 kg dry ingredient?
Show answer and reasoning
No; it contains 0.9 kg dry matter under the stated composition.
Wet paste includes 8.1 kg water in the two-part account. Later processing and acceptance may alter usable output.

Key ideas

Track cultivated identity, product form and intended use through processing.
Separate wet mass, dry matter, target recovery and chemical amounts.
Assess chemical, microbial and physical hazards for the actual product and process.

References

Sources supporting the explanations and examples in this article.