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Do Overnight Oats Need To Be Refrigerated?

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Instead of the standard cooked oatmeal preparation, overnight oats are made by soaking the grain in your favorite liquid. The raw oats become soft and digestible, transforming into a delicious and nutritious meal prep. 

Typically, you store oatmeal in a cool, dry and dark area, but once it is cooked it must be refrigerated to minimize the risk of food borne illness. But what about preparing overnight oats, do they need refrigeration while soaking?

Do you need to refrigerate overnight oats? Yes, it is recommended to refrigerate overnight oats while soaking, however it can also be made without refrigeration. The oats will ferment at room temperature, and although people have been fermenting food for thousands of years this goes against modern food safety guidelines.

Overnight oatmeal is made by soaking raw oats in liquid instead of cooking them with heat. The soaked oats are edible without cooking as they become soft and digestible after absorbing the liquid. 

Preparing Overnight Oats

If you have never tried overnight oatmeal, then you are in for a treat. Start by learning how to make overnight oatmeal and preserve them, provided in this guide are facts about the refrigeration of overnight oats and everything you need to know about the process.

Do the oats need to be soaked?

When you want to eat oats without cooking them, then you should soak them in liquid overnight to make a delicious non-cooked oatmeal. Soaking makes your oats easily digestible by giving them a creamy, soft and silky texture. 

The texture of overnight oats resembles that of traditionally cooked oatmeal. So, you can eat them without spending time on cooking them in the morning. 

You can eat overnight oats cold, room temp or heat them to give a similar look to freshly cooked oatmeal. The final temperature of the oats does not impact the digestibility of the grain.

How long do overnight oats take?

The method of making overnight oats requires soaking them in liquid for the night, then eating in the morning the very next day. In order to successfully reduce phytic acid in overnight oats, you should soak them for at least 12 hours.

A single serving of oats in half a cup, but you can add as much oats as you want to eat. Add some toppings like dry fruits and other healthy ingredients, fill with your preferred liquid and cover with a lid. 

At this point, you can choose to leave the oats at room temperature or refrigerate to reduce the amount of fermentation. Allow the mixture to soak overnight so that it is ready to eat in the morning. 

Can you leave overnight oats at room temperature?

Yes, you can leave overnight oats at room temperature but for a limited period. Initially, oats should be soaked at room temperature instead of being placed immediately into a refrigerator. 

The liquid can also be heated to slightly warmer than room temperature before submerging the oats. Soaking overnight oats at a slightly warmer temperature than room temp actually makes them more nutritious.

Basically, it’s understood that you cannot eat oats raw. Traditionally, whole grains have been eaten either after fermenting or cooking. 

Refrigeration is a relatively modern invention, and earlier people used to prepare whole grains by fermenting or soaking them to avoid various illnesses and make the grains more digestible. They used to soak whole grains at room temperature and allow them to ferment as refrigerators were not available. 

But nowadays, people do not enjoy the slightly sour and tangy taste of fermented whole grains. So after soaking oats for 4-5 hours at room temperature, you can refrigerate overnight oats to slow the growth of the beneficial bacteria. 

Fermenting at room temperature will help to introduce the nutritious elements of fermentation, similar to yogurt, sauerkraut or wine. Refrigerating will slow the process and reduce the speed of fermentation.

How long can Overnight Oats stay out of the fridge?

Depending on the recipe, temperature of the room and comfort with eating fermented foods, you can safely leave overnight oats out of the fridge for 12 to 24 hours without any concern. 

Dry oats can be stored in your pantry for years without any problem, but once you have soaked then in a liquid you cannot leave then at room temperature for a long time. The microorganisms found in oats will start growing at a faster speed after they are soaked in a liquid. 

The warmer the room temperature, the faster the organisms multiply. When left at warmer temperatures for too long, the oats can over ferment and become inedible.

In general, most people prefer to refrigerate overnight oats after leaving them at room temperature for about 4-5 hours. This will allow for some growth of beneficial microorganisms, but slow the process so that the oats don’t taste too fermented or sour.

Do you have to put overnight oats in the fridge?

You do not have to put overnight oats in the fridge right away. Soaked oats can easily remain at room temperature for 12 to 24 hours without any concern.

After soaking oats in liquid for 4-5 hours at room temperature, it is common for people to put overnight oats in the fridge as microorganisms found in oats can start growing at faster speed once they are soaked for longer periods of time. 

Over fermenting is a mistake, so leaving soaked oats without refrigeration for too long will make them inedible. So, it is essential to understand the process of fermentation and learn how the temperature of your environment has an effect on the microorganism growth.

For more information on this subject, we high recommend this book on fermentation. It covers the fermentation of oats and grains with easy to follow recipes and instructions.

Does oatmeal spoil if not refrigerated?

Yes, oatmeal will spoil if not refrigerated. Once dry oats have been exposed to water, bacteria multiplies quickly and can cause the oatmeal to spoil.

Though the shelf life of uncooked or dry oats is up to 30 years, when it is cooked or soaked then the stability is compromised depending on how it was prepared.

Cooked oatmeal should be refrigerated within two hours of finishing the process, whereas you should refrigerate overnight oats after soaking them at room temperature for 4-5 hours.

You can maximize the shelf life of cooked or soaked oatmeal by refrigerating them in a reseal-able plastic bags or an airtight covered container. Cooked oatmeal can be reheated without spoiling for 4-5 days if stored properly in the fridge. 

The reason behind it is that bacteria can grow in the oatmeal when it is kept at room temperature, this will eventually spoil the texture and taste. If cooked oatmeal if left at room temperature for more than 2 hours, then it should not be refrigerated and reheated.

You can extend the shelf life of prepared oatmeal even more than 6 months if packed properly in airtight containers or freezer bags and stored in the freezer. Prepared oatmeal can be preserved for a long time if stored properly at 0 degree F in frozen condition, that includes overnight oats too.

When oatmeal has gone bad, then its taste, texture and smell will change, and you should discard it right away.

Is it ok to freeze overnight oats?

It is absolutely ok to freeze overnight oats, however it is best used when you are meal prepping for next week or beyond 4-5 days.

It is essential to refrigerate overnight oats to avoid the rapid growth of microorganisms, but it is not necessary to freeze them if you want to consume the very next morning. 

Though overnight oats are soaked at room temperature in liquid, they cannot be left at room temperature indefinitely. They have to be refrigerated eventually, and most people stick with 4-5 hours to deter the rapid growth of microorganisms. 

Overnight oats can be frozen if you have to consume them after a few days, weeks or up to 6 months.

Do you need to refrigerate overnight oats?

Room Temperature Overnight Oats: Final Thoughts

The information provided in this write-up helps in knowing the importance of refrigerating overnight oats and why it is necessary. Though overnight oats can be prepared by soaking oats in liquid and leaving it at room temperature, it cannot be left indefinitely on the countertop of your kitchen.

If you leave soaked oats at room temperature, they will begin to ferment. Fermentation has been practiced for thousands of years as refrigeration is a relatively modern invention.

Soaked oats can be left to ferment at room temperature for 12 to 24 hours. Fermentation is slowed by time and temperature, and refrigeration helps to control this process.

If you leave soaked oats out of the fridge for too long, it will spoil due to the rapid growth of microorganisms. So it is recommended to refrigerate overnight oats after soaking them at room temperature for 4-5 hours.

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Wednesday 31st of August 2022

Hello, which is better in order to get rid of the phytic acid and to benefit from the nutrients refrigerating or leaving the oatmeal outside? And if I refrigerate it how long should it be in the refrigerator after I leave it outside for about 4 hours?


Thursday 1st of September 2022

The oats need to be fully hydrated, which takes about 8 to 12 hours. After that, length outside the refrigerator will produce a slightly sour taste due to fermentation. To make the overnight oats less sour, then place them in the fridge instead of leaving at room temperature.


Tuesday 16th of August 2022

Thank you the information/content on your site.



Tuesday 16th of August 2022


Thank you the information/content on your site.

What are your thoughts on placing the overnight oats in the refrigerator right away after soaking them in water. And then taking them out in the morning, letting continue to soak at room temperature until about 16:00 or so?

Roughly soaking in the refrigerator from about 18:00 to about 06:00 and then from about 06:00 until about 16:00.

Thank You, ML


Tuesday 16th of August 2022

In the end, you are activating the fermentation process in the oat by combining the grain with water and leaving it at room temperature for an extended period of time. The real question is how warm is the room that the oats are left in?

At room temperature, there should be very little concern. However, if the temperature in the room is considerably warm or hot than the oats will ferment more. Nothing wrong with this, but a slightly sour flavor will develop that is comparable to other fermented foods.

Some people really enjoy an slightly fermented flavor, but it is definitely not for everyone. The longer you leave the overnight oats at room temperature and do not refrigerate, the more fermented it will taste. I would recommend a maximum of two or three days at room temperature without refrigeration before it gets to funky, no matter what the temperature may be.

Enjoy, -Joshua


Tuesday 5th of April 2022

Would it be safe to leave overnight oats on kitchen counter (instead of refrigerating it) if they are soaking in 1 cup almond milk and 1/2 cup of yoghurt? Will the milk and yoghurt be ok for 12 hrs?


Tuesday 5th of April 2022

It should be perfectly fine. Yoghurt is made by fermenting milk, which is essentially leaving it at room temperature, and there is nothing wrong with fermenting almond milk for that long as well. Look, smell then taste a small bite to make sure everything is good before diving in.

If you still have concern about leaving almond milk and yogurt on the counter for 12 hours, then just soak the oat in water for that amount of time, then add the cold almond milk and yogurt just before serving.

PT Baietto

Monday 23rd of August 2021

Hi Joshua, Just wanted your thoughts on using some Kombucha in the overnight soak? Any benefits or problems? I usually put in some ground cinnamon, but I’m going to start adding walnuts or sunflower seeds. Thanks, PT


Monday 23rd of August 2021

Hello, thanks for reaching out. Kombucha is an interesting choice and not something I have done before, however i have made overnight oats with coffee and tea. Nuts, seeds and spices are always a good choice and something we frequently add to our best overnight oats recipes. You asked about kombucha, so let me share the initial thoughts that come about. Adjust the amount of sweetness to the recipe because kombucha will have added sugar. If you are looking for the fermented benefit from adding kombucha, skip the kombucha and ferment the oats instead by leaving them at room temperature overnight. Kombucha can be expensive at $3 a bottle and the cost add up quickly if you don't make it yourself. I believe that there is really nothing wrong with adding kombucha to overnight oats, so please share your results if this is something you do end up trying. Kindly, Joshua