Should Slow Cookers Have a Hole in the Lid? What Is It For?

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I noticed something the other day when I was at a cook-off with slow cookers. I realized that some slow cookers come with a hole in the lid, and some do not. I could not help but wonder, should slow cookers have a hole in the lid? I did some research and found the answer to my question to be a little more complex than I initially thought.

What is the hole in the lid of the slow cooker for, exactly? 

The hole in the lid is a vent that allows heat and pressure to be released during the slow cooking process. Without a little ventilation, the pressure from heat and water could cause the contents to boil over, sputter, and potentially cause burn hazards. 

Think of what happens when you leave a pot of boiling water on the stove. Eventually, the pot gets too hot, and the water boils over. Often, slow cookers automatically adjust to this loss of pressure from heated water vapor and adjust the temperature accordingly.

Still, why do some slow cookers have a hole in the lid, and some do not? To answer this question, we should understand how a slow cooker and its parts work. 

How slow cookers work

A slow cooker works similar to a regular pot one would cook on the stove. The heating element is at the bottom, and the heat expands throughout the container. Most commercial slow cookers can be broken down into three separate parts: the heating element, the pot aka “the crock,” and the lid. 

The heating element

Slow cookers have what is called “the heating element,” which is surrounded by metal casings. This is the slow cooker’s heat source. There are usually two metal casings that cover the heating element on both sides. The metal casings also serve as a barrier between the crock and the heating elements, so the two never come into direct contact with one another.

Most heating elements have at least two heat settings; low, high, and some will have a “keep warm” setting. Depending on the type of slow cooker, there may be more heat settings. 

The crock

The crock serves as the vessel which the food occupies, as well as a reservoir for retaining heat.

It is a pot that rests inside of the heating element and the metal casings. It is usually composed of extremely glazed and thick ceramic stoneware. Some have a metal interior that is lighter and allows for fast heating. I explain the benefits of ceramic inserts over metal ones in my article on the best slow cookers.

The ceramic crock is so good at retaining heat, it can keep food hot for long periods after cooking. This makes crock pots ideal for bringing food to share at a picnic or gathering.  

The lid – should slow cookers have a hole in the lid?

The lid is usually made of glass and covers the top of the crock. This allows the warm water vapor to stay trapped inside the slow cooker. Most, but not all, lids usually sit on grooves, which creates a light seal and slight pressure inside the crock. The lid is essential to protecting warm vapor from escaping. 

When higher temperatures inside the crock are reached, the steam expands too much, causing the slow cooker lid to raddle or pop off completely.

Why does a slow cooker lid have a hole in it?

Sometimes slow cookers, especially those that can cook at high temperatures, will include a lid with a small hole to allow a small portion of the steam to release and reduce pressure. Those without small holes will release pressure along the sides of the unsealed lid.

As well, some slow cookers have a dual purpose vent in the lid. Different types of slow cookers will have different types of attributes and uses.

Types of slow cookers

While there are multiple ways to categorize slow cookers. Many options are available for how slow cookers are shaped or programmed. For this article, we will keep it simple by separating slow cookers into three main sizes; small, medium, and large. 

Small slow cookers

  • Small slow cookers are roughly 1-2 quarts in size, and are perfect for those little sausages, making cheese dip, or single-serving dishes.
  • Typically, the small slow cookers do not have a hole on top, and pressure is allowed to vent along the sides of the lid. 

Medium size slow cookers

  • Medium size slow cookers are the most popular type of slow cooker and range from 3-4 quarts.
  • These are perfect for making dinner for the family, larger servings of sauces and dips, or a big pot of beans and soups.
  • Many of these slow cookers will have a hole in the lid or will allow pressure release from the sides.

Large size slow cookers

  • Large size slow cookers range from 5-6 quarters and are perfect for large crowds and meals.
  • For a family dinner, a large size slow cooker recipe may consist of meats and additional ingredients.
  • Because it is capable of making such a large amount of food, this size slow cooker may work best for the larger social events and functions.

There are larger slow cookers, which are 7 quarts or more and are usually used by professional caterers and banquets staff. As with the small and medium-size slow cookers, there may or may not be a hole in the lid, depending on the amount of sealing power the lid has along the sides. 

I also wrote: Is it safe to leave food in the crockpot overnight?

The dual-functioning hole in lid of slow cooker

Some slow cookers have a hole in the lid that also functions as a meat probe. These holes are typically padded with heatproof rubber lining. The hole still allows for ventilation, but also provides an entrance to the container for the cook to insert a meat thermometer.

The meat probe is the most ideal way of checking the internal temperatures of food, as lifting the lid to check will allow too much heat to escape the crock. This also allows the cook to ensure that food reached an internal temperature that is safe to consume. 

Remember, when cooking, especially with heating elements, safety comes first!

Slow cooker safety guidelines 

Speaking of safety (and from personal experience), it is important to acknowledge some cautions when using slow cookers for making delicious food. 

  1. Do not cover up the hole in the lid. This hole is there to help relieve the inside of the crock from building too much pressure. Some will try to cover the hole with a cloth or aluminum sheet to trap the steam, but excessive pressure inside a slow cooker can put you and your slow cooker risk. Too much pressure can cause a slow cooker to explode. 
  2. Slow cookers are great for setting and forgetting but do not forget about your slow cooker while it is in use. One time, I forgot that I was making apple butter and left home for more than 24 hours, only to come home to a ruined crock and home that smelt like burnt jam. This is also a huge fire hazard. Luckily, I did not burn down the apartment complex. 
  3. Do not underfill your slow cooker of liquids. Ensure there is enough liquid inside the slow cooker for best results. Little to no liquid can cause the food to burn. 
  4. Slow cookers can get very hot. If you’re cooking for a crowd, and plan to transfer the crockpot to another location, be sure to use protective gloves, or simply place your hot slow cooker in a sturdy, cardboard box, preferably one with handles on the side. Do not use flimsy boxes. Another great advantage of using a box is it will also protect your car from any potential spillage during transportation. 
  5. Do not use frozen ingredients. Slow cooking is, well, slow. This means that if you put frozen food into a slow cooker, it may not reach an internal temperature that is safe for consumption in a few hours. Food and safety best practices recommend ensuring food has reached an internal temperature of 140 degrees within four hours. If you plan to use frozen foods, especially meats, it is a great idea to thaw your meats a day or two before cooking in a slow cooker. 
  6. Wait for the crock to cool down. If the crock is hot and is exposed to cooler temperatures, it may crack or shatter completely. Before washing the crock, especially in cold water, allow it to cool down. Do not set the slow cooker outside in cold temperatures. A broken crock can cause sharp pieces of porcelain to break off and potentially cut or injury someone.

I also wrote: About the pros and cons of using slow cooker liners

Tips when using a slow cooker with hole in lid or not

Generally, you use less liquid in a slow cooker than you would in a pot on the stovetop. Even with a hole in the lid, moisture will drip back into the crock and add liquid to the contents. But when cooking food like pulled pork you don’t want that extra moisture dripping back into your food. The trick is to place a folded length of paper towel across the pot, under the lid. This tip and more are covered in this video.

See also: Things to cook in a pure ceramic pot

Info sources

WPo: Bit of history on the slow cooker

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