Screening, Separating and Rinsing the Eggs

Before caviar becomes a spoonful of loose beads, it is a cohesive mass of eggs bound in ovarian tissue. The University of Florida's aquaculture guidance describes the transformation: handfuls of ovary are gently rubbed over stainless steel screens, releasing individual eggs into a container below.

The task is to remove tissue and loose contamination without breaking the beads destined for salting. Gentle handling, water suitable for direct food contact, thorough drainage and a documented cold processing sequence make that possible.

Screening, separating and rinsing the eggs: what reaches the screen

An extracted ovary brings more than eggs to the processing table. The surrounding ovarian membrane and connective tissue must come away, along with fat tissue, blood clots and fragments of ovarian follicles, the structures that enclose developing eggs.

This is the conventional preparation route for eggs collected within the ovary. Ovulated eggs have already been released from their follicles and need a different route, a distinction recognised by Codex. For the surrounding production sequence, see from fish to tin.

Screening and separating the eggs

The eggs should pass through the screen; the supporting tissue should stay above it. Florida's guidance describes cutting the ovary into manageable pieces, then gently rubbing handfuls over stainless steel screens into a receiving container. The aim is separation, not forcing every last egg through the openings.

Screen aperture is the size of those openings, not the wire thickness or an unspecified mesh number. Codex says the mesh should match egg size but provides no species-by-species aperture schedule. The primary sources reviewed did not establish reliable numerical screening apertures for individual sturgeon species, so no such figures are prescribed here.

Choose and verify the screen against the actual batch. It must release eggs without damaging pressure while retaining the tissue being removed. Published egg diameters cannot replace validated screen specifications. For the biological distinction between supporting tissue and the egg's own envelope, see the egg membrane.

What machines can and cannot replace

Size grading and tissue separation are different jobs. Mechanical screening for size grading is documented; reliable mechanical separation of eggs from ovarian tissue has not been documented.

Chinese utility model CN210386551U, published in 2020, describes a motor-driven reciprocating screening box with one or more mesh layers. Its stated purpose is to grade eggs by size, rather than detach ovarian tissue with acceptable egg damage.

A patent records a design and its applicant's claims, rather than independent commercial validation. Before replacing hand separation, a processor needs evidence that the equipment performs the intended task: intact-egg recovery, residual tissue and cleanability all matter. Faster size grading alone answers none of those questions.

Rinsing: water quality before water temperature

Rinsing carries away blood, broken eggs and loose tissue left after screening. Florida's guidance describes several rinses in chilled clean water. The water may run clear, but rinsing is a cleaning step, not a validated microbial kill step or confirmation that the eggs are safe.

Use chilled potable water, meaning water of drinking quality, and verify the supply at its point of use. Neither the Codex caviar standard reviewed nor the Florida processing account establishes a universal numerical rinse-water temperature. A finished-product storage temperature is not a rinsing instruction.

Set the rinse-water limit and monitoring requirements in the plant's documented process. “Cold” alone is too vague. Record product exposure too: chilled water cannot account for time spent waiting between the screen, rinse vessel and drain.

Which water rules apply

In the EU, Regulation (EC) No 852/2004, Annex II, Chapter VII, requires an adequate potable water supply where needed to prevent food contamination. Its allowance for clean water with whole fishery products does not give blanket permission to wash separated roe. Directive (EU) 2020/2184 provides the drinking-water framework, implemented through national law.

In Great Britain, Regulation (EC) No 852/2004 applies as assimilated and amended law, alongside the drinking water requirements applicable in England, Wales or Scotland. The FSA's official controls manual explains potable water requirements for England and Wales. Northern Ireland applies the relevant EU hygiene framework alongside its local drinking water requirements.

The water may run clear, but rinsing is a cleaning step, not a validated microbial kill step or confirmation that the eggs are safe.

In the US, 21 CFR 123.11 requires sanitation monitoring covering water that contacts food or food-contact surfaces. Section 117.37 requires an adequate supply and safe water of adequate sanitary quality for food contact. Seafood HACCP compliance does not remove the applicable current good manufacturing practice requirements.

Drain before weighing and salting

Let rinse water escape through a suitable draining sieve. Do not squeeze the eggs. This drainage before salting is a separate operation from removing excess brine after salting; the Codex processing flow distinguishes the two.

Surplus rinse water changes both the weight on the scales and the water available to dissolve salt. Material weighed with that surplus is not simply drained roe. A fixed salt addition calculated from its wet weight therefore cannot be assumed to deliver the intended final salt concentration.

That relationship explains why drainage matters; checking the finished product remains essential. The subsequent controls belong in salting caviar.

Faults to catch at this stage

Broken eggs cannot be repaired. Catching excess pressure, lingering tissue or poor drainage now allows the process to be corrected, but does not guarantee recovery of affected material. Hold it for assessment under the plant's procedures.

The responses below follow from the handling guidance in sources 1 and 2.

Soft texture does not identify a single processing error. Codex lists objectionable odour, flavour and consistency as defects, and rinsing cannot be relied on to correct them. See off-flavours and texture problems.

Time, temperature and hygiene

Keep the sequence cold and as short as practicable. That is the Codex recommendation, rather than a single stopwatch limit for every plant. FDA seafood guidance likewise treats cumulative time and temperature exposure as a hazard-control question.

Establish limits through the site's hazard analysis and validation, then monitor the whole sequence. The clock does not reset when eggs move from one vessel to another.

Keep egg processing separate from belly cutting and gutting. Use trained staff, washable food-contact screens and cleaned, disinfected utensils. Prevent contamination from hands, water and surfaces, and choose cleaning agents that do not taint the eggs.

These prerequisite hygiene controls protect the process; visible cleanliness alone cannot establish microbiological safety. The caviar processing hub places them within the wider production system.