# What is a hairline crack in an egg? > A hairline crack is a crack so fine that it does not show under normal light, so an ordinary camera does not see it. It is revealed by candling, with light behind the egg, or by acoustic testing, which picks up a change in the shell's response. Vigiovo detects only cracks visible in the image. Updated: 2026-10-09 · URL: https://vigiovo.com/en/resources/hairline-cracks-in-eggs · Português: https://vigiovo.com/recursos/trinca-capilar-no-ovo.md ## Key takeaways - A hairline crack is too fine to show under normal light, so an ordinary camera does not detect it. - It is revealed by candling (light behind the egg) or by acoustic testing. - Class A requires an intact shell (RIISPOA, art. 225): a crack that breaks the shell takes the egg out of Class A, however fine. Internal cracks visible only on candling are treated by MAPA as fissured eggs (question 3). - Hairline describes how fine the crack is; a fissured egg describes where the crack formed (MAPA, question 3). ## What is a hairline crack? A hairline crack is a crack so fine that it does not show under normal light. The term describes how fine the crack is, not what caused it. Two rules matter in grading. Class A requires an intact shell (RIISPOA, art. 225), and egg establishments must carry out candling (RIISPOA, art. 223). A hairline crack shows up only in that check or in acoustic testing. ## Why does a camera miss a hairline crack? A camera records the image under normal light, and a hairline crack does not show in that light. On the surface image the line is too fine to stand out from the shell, so there is nothing for the system to measure. That is why a camera cannot replace candling, which remains mandatory (RIISPOA, art. 223). A camera is useful for defects that appear in the image, such as visible cracks and dirt, but that is a different part of the problem. In practice, a line that relies only on a camera lets hairline cracks through. For that reason, grading should combine the camera with candling or acoustic testing, and not treat the camera as a substitute for them. This applies both to the grading line and to the decision on where the egg goes. ## How is a hairline crack detected? Two methods reveal it: candling and acoustic testing. - **[Candling](https://vigiovo.com/en/resources/glossary#candling)**: the egg is held against a strong light, and the crack shows through the shell. - **Acoustic testing**: the shell's sound response changes when there is a crack. **Which method reveals a hairline crack** | Method | Reveals hairline crack | Note | | --- | --- | --- | | Surface camera | No | Sees visible cracks and dirt | | Candling | Yes | Depends on the operator or the equipment | | Acoustic testing | Yes | Done on dedicated equipment | No single method catches every defect. A hairline crack and a fissured egg are different cases, and the difference is explained in [body-checked eggs](https://vigiovo.com/en/resources/body-checked-eggs). ## Does Vigiovo detect hairline cracks? No. Vigiovo only detects cracks visible in the image, so a hairline crack is outside what it analyses. It still needs candling or acoustic testing. Vigiovo complements those checks by removing dirty eggs and visibly cracked eggs before them, so candling works on a cleaner batch. Details in [how it works](https://vigiovo.com/en/how-it-works). ## Frequently asked questions ### Can a camera detect hairline cracks? No. A hairline crack does not show under normal light, so an ordinary surface camera does not see it. It requires candling, with light behind the egg, or acoustic testing. A camera helps by removing visible cracks and dirt before those checks. ### Does a hairline crack take an egg out of Class A? If the crack breaks the shell, yes: Class A requires an intact shell (RIISPOA, art. 225). But internal cracks visible only on candling, formed in the hen's uterus, are treated by MAPA as fissured eggs that can still be Class A (question 3). Candling decides between the two. ### What is the difference between a hairline crack and a fissured egg? A hairline crack describes how fine the crack is. A fissured egg describes its origin and exposure: internal cracks formed inside the hen's uterus that do not expose the inside (MAPA, question 3). An egg can have a hairline crack without being fissured, and a fissured egg shows only on candling. ## Sources - [Perguntas e respostas sobre a Portaria MAPA nº 612/2022 (versão de 05/06/2023)](https://wikisda.agricultura.gov.br/manual_ovos/perguntas_e_respostas_port612_2023.pdf), Ministério da Agricultura e Pecuária (MAPA) - [Decreto nº 9.013/2017 (RIISPOA)](https://www.planalto.gov.br/ccivil_03/_ato2015-2018/2017/decreto/d9013.htm), Presidência da República (Brasil) ## Read next - [The egg air cell: the 6 mm limit explained](https://vigiovo.com/en/resources/egg-air-cell.md) (Explainer, 2026-10-09): The Class A air cell limit of 6 mm and stationary under RIISPOA art. 225 and EU Regulation 2023/2465, why only candling measures it and a camera cannot. - [Leaker eggs: definition, risks and destination](https://vigiovo.com/en/resources/leaker-eggs.md) (Explainer, 2026-10-09): What a leaker egg is under 7 CFR 57.1, why RIISPOA makes it unfit for consumption, what a camera can see and how to handle it on the line. - [How to identify cracked eggs: types, methods and rules](https://vigiovo.com/en/resources/how-to-identify-cracked-eggs.md) (Guide, 2026-10-09): What a cracked egg (check) is, how it differs from a leaker, which methods detect each kind of crack and where cracked eggs must go under the regulations. ## 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. https://vigiovo.com/en/how-it-works.md 3 min read.