Most of us know what it means to boil a food. We do it with dried pasta when we bring water to a rolling boil and put in the pasta. Even if we reduce the heat of the burner to stop the pot from boiling over, we are still boiling the pasta. But, what does it mean to simmer, or to poach?
The most precise way to understand the difference between these three cooking methods is to know the temperature ranges they use. Below, I’ll explain the relative temperature ranges and describe the methods briefly so that you will have a much better idea of what these terms mean when you encounter them in cookbooks and recipes.
To start, know that all these moist-heat cooking methods have one thing in common: They all involved submerging foods in heated water, stock, broth, or other liquids.
What is Boiling?
I’ve already explained a great deal about boiling while debunking the myth that adding salt to water helps pasta cook faster and…
At sea level, water boils at 212°F or 100°C. This is the point at which the water begins to turn to steam (vapor). This vapor forms within the water and when an appropriate pressure is reached, the water begins to boil. This is when the vapor bubbles, which have formed on the bottom and the sides of the pan, are released, causing the bubbly boiling effect we see.
So, to boil a food is to cook it in a liquid that has reached this critical point and it bubbling rapidly. The water, during a boil, will be agitated and full of energy. One thing to understand is that no matter how much you turn up the burner, the temperature of the liquid is not going to get any higher. So, a boil is a boil. Although the size of the “bubbles” and the apparent energy of the water seem to increase, the temperature is the same with higher settings. Since the temperature of the water does not increase with a more violent boil, there is no advantage to cooking foods at anything more than a “gentle boil.” So, once you add food to boiling water and return the water to a boil, it is best to reduce the setting of the burner so that it is just high enough to maintain a gentle boil, thus helping to eliminate spill-overs. The food will cook at the rate, so long as the water is actually boiling.
Boiling is usually only used for starches such as potatoes, dried pasta, beans, and vegetables with tough fibrous textures. It is also used for certain food items which are only being heated up to a certain point but will not be greatly affected by how they are cooked, such as hot dogs or canned soups, but even these can be cooked at lower heat settings, so long as they reach a proper minimum temperature.
Boiling is unsuitable for delicate foods, which may be torn apart by the agitated water, and it may cook certain foods too rapidly. For example, a piece of delicate or medium-firm fish should never be boiled. When vegetables are boiled for long periods, nutrients can be lost to the water.
Once you decrease the temperature of the water to a level where the vapor in the water is not at a sufficient pressure to overcome the pressure of the atmosphere acting on the water, the water is no longer boiling.
What is Simmering?
The term simmering is often confused with a gentle boil. However, a simmer is not really a boil. Suggested temperature ranges for simmering vary slightly, but they are commonly no higher than 200°F and no lower than 180°F. A range up to 205°F is sometimes suggested, but as long as you are maintaining a temperature somewhere in between these ranges, you are simmering. Basically, a simmer is “just below a boil.” Personally, I would advise a temperature range between 185°F and 205°F.
Simmering is, in reality, the most oft-used method of cooking in water, even though the term boiled might be used to describe the food after it is cooked. Some confusion is caused by the presence of bubbles. During a simmer, vapor bubbles will form on the sides and bottom of a pan. When using plain water you may easily be able to see these bubbles forming. These bubbles should disappear when you stir the liquid.
Depending on the composition of the liquid and the amount of time spent simmering, and the occasional bubble may break the surface. As long as a full boil is not reached, it is still simmering.
Poaching is done at a lower temperature still than simmering using temperature ranges from 160°F to 180°F. Paradoxically, though, these lower temperatures do not always mean longer cooking times than simmering. Poaching is ideal for very delicate foods like fish, eggs out of their shell, and some fruits. It can also be used for chicken. All sorts of different liquids, besides water, are used for poaching, such as broth, stock, wine, juice, or a combination of any of these. Milk can also be used for poaching and even oil.
1. Marcus, Jacqueline B. Culinary Nutrition: the Science and Practice of Healthy Cooking. Elsevier/Academic Press, 2013.
2. Gisslen, Wayne. Professional Cooking. 7th ed., John Wiley and Sons, 2010.
3. Brown, Amy. Understanding Food: Principles and Preparation. Belmont, Calif., 2008.
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