Does the yolk have to be in the centre of the egg?

The rule does not fix an exact point. It asks that the yolk show as a shadow and return to the central position after the egg is turned (RIISPOA, art. 225, III). A yolk that does not move or does not return to the centre should be checked and recorded.

Does a yolk stuck to the shell make the egg unfit?

Yes. Under RIISPOA, eggs with a yolk stuck to the shell or a broken yolk are unfit for human consumption, as they are found (art. 500, I). The condition is inside the egg, so it shows only on candling.

Can a camera see the yolk of an egg?

No. A surface camera records the shell, and the yolk is inside the egg. The position and movement of the yolk are observed on candling, which is mandatory in registered establishments (RIISPOA, art. 223).

Explainer · Defects and grading

What does a normal yolk look like on candling?

On candling, a normal yolk appears as a shadow, with an apparent outline, that moves slightly when the egg is turned and returns to the central position (RIISPOA, art. 225, III). A yolk stuck to the shell or broken departs from this pattern and makes the egg unfit for consumption. The yolk lies inside the egg, so only candling checks it; a surface camera cannot see it.

Updated October 9, 2026 · 4 min read

What does a normal yolk look like on candling?

A normal yolk appears on candling only as a shadow. RIISPOA asks that this shadow have an apparent outline (art. 225, III). The European regulation describes the same shadow in other words, as a shadow without a clearly discernible outline (Delegated Regulation (EU) 2023/2465, art. 3(1)(c)).

The two texts agree that the yolk is seen only as a shadow. They differ on the outline. In Brazil, the reference is the RIISPOA text, and how the outline is read should follow the establishment's criterion, recorded in its procedure.

Should the yolk move when the egg is turned?

Yes, slightly. A Class A yolk moves a little when the egg is turned and returns to the central position (RIISPOA, art. 225, III). The European rule has the same movement: the yolk is slightly mobile when the egg is turned and returns to a central position (Delegated Regulation (EU) 2023/2465, art. 3(1)(c)).

This movement is what separates a loose yolk from a fixed one. A normal yolk shifts a little and returns to the centre. Because the texts give no angle and no time, the operator checks it, following these steps:

Turn the egg slowly under the light and watch the yolk shadow.
Check whether the shadow returns to the centre after the turn.
Set the egg aside if the yolk does not move or does not return to the centre, and record the case.

When does the yolk position become a defect?

A yolk position becomes a serious defect when the yolk is stuck to the shell or broken. In those cases the egg is unfit for human consumption, as it is found (RIISPOA, art. 500, I).

A yolk off the centre that stays still is not in the list of art. 500. It may be a sign that the egg needs checking, but the cited texts give no positional criterion. That reading is practical and should be recorded by the establishment.

Reading the yolk on candling
Observation	What the rule says	Basis
Shadow that moves when turned and returns to the centre	Class A pattern	RIISPOA, art. 225, III
Yolk stuck to the shell	Unfit for human consumption	RIISPOA, art. 500, I
Broken yolk	Unfit for human consumption	RIISPOA, art. 500, I
Shadow that does not move or does not return to the centre	No numerical criterion in the text; check and record	Establishment practice

The last row of the table is practical judgement, not a quoted rule. For the white and the other internal requirements, see Class A egg white.

Why does only candling check the yolk?

The yolk lies inside the shell and the membrane, and a surface camera records only the shell. Vigiovo therefore does not assess the yolk: it works on the shell and classifies each egg as clean, dirty, cracked or unverified.

The yolk position is observed on candling, a step required by RIISPOA (art. 223, II). Vigiovo can reduce the visible dirt and cracks that reach it, but the yolk is still checked inside the egg. For what Vigiovo does, see how it works.

Frequently asked questions

Does the yolk have to be in the centre of the egg?: The rule does not fix an exact point. It asks that the yolk show as a shadow and return to the central position after the egg is turned (RIISPOA, art. 225, III). A yolk that does not move or does not return to the centre should be checked and recorded.
Does a yolk stuck to the shell make the egg unfit?: Yes. Under RIISPOA, eggs with a yolk stuck to the shell or a broken yolk are unfit for human consumption, as they are found (art. 500, I). The condition is inside the egg, so it shows only on candling.
Can a camera see the yolk of an egg?: No. A surface camera records the shell, and the yolk is inside the egg. The position and movement of the yolk are observed on candling, which is mandatory in registered establishments (RIISPOA, art. 223).

Sources

Decreto nº 9.013/2017 (RIISPOA), Presidência da República (Brasil)
Delegated Regulation (EU) 2023/2465, marketing standards for eggs, EUR-Lex

How Vigiovo helps

Vigiovo grades eggs on the conveyor as clean, dirty, cracked or unverified, in real time, with deterministic computer vision: every decision comes with the measurements behind it, on an ordinary CPU.

See how it works