Posted by Eric Troy on 13 Jan 2015 21:38
Sometimes, recipes call for lukewarm water. They may even call for lukewarm milk or some other liquid. Most often, this instruction is used for dissolving yeast for baked products, but it may be found in other recipes as well. Just what temperature is "lukewarm?"
Meaning of Lukewarm
In reality, lukewarm is a very inaccurate instruction to use in a recipe, but it usually gets the job done. There is no one agreed upon temperature or even relative scale that defines lukewarm. Some folks say lukewarm is body temperature or approximately 98.6°F. Others say it is room temperature.
Room temperature, of course, varies, but most agree it is from 72°F to 74°F (sometimes up to 78°F). Still others say lukewarm is room temperature plus about 15 degrees. Lukewarm and tepid are generally considered to be synonyms.
However, if you were running a "lukewarm bath" you would probably run the water over your hand to determine the temperature at which you could barely feel the heat or coldness of the water. In other words, you'd look for the temperature to pretty much match the temperature of your own skin. Therefore, if your skin was colder, the water would be cooler and if your skin was warmer (e.g. because you just ran hot water over it) the water would be warmer. You may hear that this temperature is generally considered to be 38°C (100.4°F).
Often, emergency procedures for emergency showers or eye-washes, such as those located in laboratories for washing off harmful chemicals, recommend that the water be lukewarm or tepid. However, it turns out this temperature has a much greater possible range than you might think. As long as the water is below 38°C (100.4°F) and above 15.5°C (60°F), it is "lukewarm" enough. This is because anything above 38° could possible enhance the chemical's interaction with the skin. It could also burn the eyes during an eyewash. On the other hand, prolonged exposure to water below 15.5°C could cause hypothermia, causing you not to shower long enough to thoroughly wash away the chemical.
Origin of the Term Lukewarm Water
The term lukewarm first appeared in printed English at the end of the 1300's. Before that, the word luke was used to mean the same thing. Luke comes from the Old English hleow, which meant warm or tepid.
Lukewarm Water Temperature For Yeast
When dealing with yeast, using tepid or lukewarm water (based on your own skin) will generally be OK. Look for the water to stop feeling cold and just feel comfortably warm but not much warmer, and you're generally good to go. Keep in mind that if your yeast has been in the refrigerator, it is best to bring it to room temperature before using. If you don't have a thermometer, you are better off with water that is a bit too cool than too hot. That is, it is better for the yeast to multiply a little less quickly than to die because the water is too hot. Yeast will work at a broader range of temperatures than people are usually led to believe. However, if you do have a thermometer, there are some basic temperature ranges to go by, depending on the type of yeast and how you are using it.
If you're using active dry yeast, go by the package directions. Generally, active dry yeast is dissolved in water with a little sugar before being added to dry ingredients. Here are the instructions for Red Star Active Dry Yeast.
Another type of dry yeast, which is sometimes called instant yeast, goes by several different names such as fast-rising, fast-acting, rapid-rise, etc. These dry yeast products are meant to be added directly to dry ingredients, skipping the step of dissolving in warm water. Here are the instructions for Red Star Quick Rise and other instant yeast products.