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A sudden change in temperature can cause the shell to crack. To prevent this, first place your eggs in a pot of cold water and bring the water to a boil over medium heat. Most importantly, avoid boiling the water while it is boiling. Boiling water can cause thermal shock and cracks in the shell, as the eggs are violently hitting each other early in the cooking process. Slow, controlled cooking over low, even heat will prevent it from bursting. Plus, simmering water will give a more even result.
Additional tip: If you have a kitchen thermometer, you can monitor the water temperature and make sure it does not exceed 80-90°C.
4) Add vinegar or salt to the cooking water
