The main reason for adding vinegar to the water when poaching eggs is because the acid in the vinegar helps to coagulate the whites in the egg more quickly resulting in them cooking quicker as well.
If the water is hot enough (near boiling), salt increases the density of the cooking liquid just enough to make the egg bob to the surface when it's about perfectly done. While you can certainly poach eggs without the salt and vinegar, they'll want to sit on the bottom of the pan and thus cook unevenly.
Do you need to add vinegar to poach eggs? Adding a splash of vinegar to the water sets the whites faster, so you have fewer wispy bits. However, if you follow the other tips this extra step usually isn't necessary.
Vinegar in the water: Never. Vinegar firms up the whites, but the viscous portion of the whites are going to firm up anyway (and the runny portion is still going to be stringy). The whites always cook faster than the yolks. Firming the whites faster with vinegar simply overcooks them before the yolks are ready.
Don't add any salt as this may break up the egg white. Stir the water to create a gentle whirlpool to help the egg white wrap around the yolk.
Heat the water: Add enough water to come 1 inch up the side of a narrow, deep 2-quart saucier. Add 1 teaspoon kosher salt and 2 teaspoons white vinegar and bring to a simmer over medium heat.
Add salt and vinegar to the water.
The salt permeates the shell a little bit, and the vinegar helps to break down the shells, making them easier to peel.
The most common things I hear of people adding to the poaching liquid is vinegar, salt, or baking soda. Vinegar does help set the albumen more quickly, which helps prevent feathering, but people with a keen sense of smell can taste the vinegar in the poached egg, which is why I don't recommend adding it.
Poaching an egg in a little vinegar helps the egg maintain its form while poaching. The vinegar helps the egg whites cook faster, allowing the egg to better stay together. Just adding about a Tablespoon of vinegar to your water can make all the difference.
As J. Kenji López-Alt explains in his book The Food Lab, salt inhibits the proteins in the egg yolks from binding too tightly as they heat up, which results in a moister, more tender curd: “When eggs cook and coagulate,” he writes, "the proteins in the yolks pull tighter and tighter together as they get hotter.
The poaching water should just barely simmer; rapid boiling will cause the eggs to break up as they cook. Poached eggs can be made ahead of time and held for up to two days. Undercook them slightly so the yolks remain runny when reheated. Refrigerate in enough water to cover the eggs.
Eggshells are made of calcium carbonate. If you soak an egg in vinegar the eggshell will absorb the acid and break down, or dissolve. The calcium carbonate will become carbon dioxide gas, which will go into the air. What is left is the soft tissue that lined the inside of the eggshell.
If you soak this egg shell in vinegar (which is about 4% acetic acid), you start a chemical reaction that dissolves the calcium carbonate shell. The acetic acid reacts with the calcium carbonate in the egg shell and releases carbon dioxide gas that you see as bubbles on the shell.
Result: When adding salt and vinegar to the poaching water, I got poached eggs of inconsistent shapes and a little bit more slimy texture. The addition made the cooking time longer but the egg was floating while cooking, as we've seen was the case when adding only vinegar.
Vinegar lowers the coagulation temperature of the proteins in egg whites. This quickly sets the outside surface of the egg forming a skin that prevents the whites from feathering out into the water.
To poach eggs, bring two cups of water to boil in small saucepan. Add one tbsp Balsamic Vinegar. Bring to boil, then bring back down to medium-low.
I like to use apple cider vinegar but it can also be white wine vinegar. Avoid using red wine vinegar because it stains the eggs a weird colour.
Add a quarter of a cup of vinegar to two litres of water. Once the water is boiling, stir it to create a 'vortex' effect. While the water swirls, pour your eggs into the water. Don't worry about separating them, they'll do this on their own.