What Happens When Cold Brew Sits Too Long? Best Tips, Method & Ratio

Cold Brew

What Will Happen When You Let Your Cold Brew Sit for Too Long?

Cold brew or cold extraction is my favorite brew, especially during the summer with soaring temperatures.

I love cold brew coffee as it has all the flavors of hot brew, but less acidic and bitter.

However, cold brewing coffee differs totally from a hot brew.

The coarse grind is the one you should use for cold extraction.

Instead of brewing for just a few minutes, brew it for an extended period.

But, if let it sit too long, it could cause over extraction and taste unpleasant.

And When Is Too Long?

Cold brew coffee concoctions left to sit longer than 24 hours could cause the extraction of some chemical compounds called catechol oligomers. It has a harsh, bitter tasting flavor. These compounds are slow-release, and they only release with over brewing.

How to Fix Your Cold Brew if It’s Too Bitter

1. Add more water

If your cold brew becomes too bitter, simply add more water to dilute the flavor and make it less strong. 

Dilute one part of cold brew with 3 parts of water.

If it’s still too bitter, you can add another part of water or chuck in some ice until you get the flavor you desired.

2. Add cream, sugar or flavored syrup

Alternatively, you can also add milk to it.

You can consider adding almond milk, soy milk, full cream or even skim milk according to your preference. It should be able to cut the bitterness and makes the coffee taste sweeter. 

If you do not fancy milk, you can infuse some syrup flavor into your coffee.

Some syrup flavors you can consider are vanilla, butterscotch, caramel, mint, maple, and cinnamon.

The 3 Most Important Factor In Steeping Cold Brew

There are several factors that affect the taste of cold brew coffee. From my research, the top three factors are extraction time, grind size and roast profile.

  • Steeping time
  • Grind size
  • Ratio of coffee to water

Adjusting Steeping Time Of Cold Brew

I use the direct immersion technique where you put in the ground coffee into water and steep. This method requires little planning because of their longer steeping time.

In cold brewing, the steeping period is typically 7 to 24 hours steeped at room temperature (20 to 25 °C or colder).

The optimal time for cold brew coffee is 18 hours, as mentioned in a coffee related study. Consumers found the flavor profile to be most appealing and enjoyable. (1).

In the brewing process, volatile and non-volatile compounds created by roasting are released into the coffee. This is the source of the characteristic coffee aroma and taste.

Does it make the cold brew solution stronger with longer duration?

The flavor extracted from cold brew coffee becomes stronger with longer duration. 

There is a scientific study to find the minimum and optimal steeping time for cold brew (1).

Here’s what they discovered.

The minimal steeping time for cold brew is 7 hours

In the scientific study, whereby the researchers measure the amount of caffeine and chlorogenic acid extracted in the solution every 30 minutes and then every hour and finally at 24h.

Initially, the amount of caffeine and chlorogenic acid extracted increases fast and gradually slows down after reaching a steady level after 7 hours.

As the cold brew coffee reaches a steady state, the amount of caffeine and chlorogenic acid in it doesn’t increase much when measured after 24 hours of steeping (2)

Thus, cold brewing should be done for at least 7 hours.

The optimal time steeping for cold brew is 18 hours

Although most of the caffeine and chlorogenic acid releases in the first few hours of cold brewing, it is best for the unique flavor of the coffee to develop with longer brewing time.

For cold extraction of coffee, the ideal time is 18 h to 22 h for maximum coffee flavors extraction. Different roasting profile, grind size could yield different results.

In a flavor and sensory study, they asked consumers to rate their likeliness based on characteristics such as acidity, bitterness, sweetness, body, and aftertaste.

Among the variations in taste profiles, customers liked cold brew coffee best at 18 hours. (1).

Consequently, cold brewing is best done over 18 hours.

What Grind Size To Use For Cold Brewing?

I recommend using the medium coarse to coarse grind for cold brew.

Because of the extended steeping time in cold temperature.

Coarse grind gives the best extraction of the coffee flavor and less acidic compare to hot extraction.

There is also a study that shows coarse grind and long extraction times (>16 h) produce the best coffee tastes, resulting in lighter body.

Nuances of notes like malt, pepper, almond, cocoa, and black fruit aroma attributes are more prominent than their hot brew counterparts.

Besides that, using a coarse grind will work well if you are using cheesecloth and metal filters.

For a paper filter, you can choose a medium coarse grind.

But if you grind too fine, it will clog up too much. It can take up to an hour for the brew to filter through. 


1:8 Ratio For Cold Brew Concentrate (By Weight)

Add 120g Coffee Ground to 1 liter of water (~34 fl oz or 4 and a quarter cup).

Do take note that the coffee ground will absorb almost a quarter of the liquid, hence you only get about 750ml of drink.

This is a double concentration that gives a potent brew.

I dilute with water in half. It is great for drinking cold or reheated. You can also add milk to it.

This double strength ratio gives you a great deal of flexibility in enjoying your drink.

It keeps its flavor better when diluted and can take more mixing ingredients.

If you prefer to drink it as it is, you can brew in single strength, just halve the coffee amount to 60g.

Top 7 Cold Brew Steeping Tips And Mistakes To Avoid

  1. Different method of processing at the farm and roasting duration at the roastery influence the flavor.
    • You should experience the brewing time of your bean. Just separate it into 2 or 3 container and let them sit for 12h, 18h, and 24h. See which one you like better.
  2. If you brew it in a refrigerator, then you can brew it longer compare to room temperature. Most of the time, though, no longer than 24 hours.
    • Do not too eager to taste your drink. Cold brew takes time to steep, leave it overnight.
  3. Use the least amount of container you can to keep the aroma and taste consistent and even. If possible, just use one container.
  4. Budget for a week’s supply.
    • If you are drinking a cup of coffee a day, then steep at least use 2 liter of cold brew.
  5. Best to grind the coffee powder when you are ready to brew.
    • Coffee ground exposed to air is subject to oxidation and fast losing the flavor and aroma.
  6. Filter the whole batch of cold brew. Do not filter the amount you wanted to drink and keep the balance unfiltered.
    • This will cause over brewing.
  7. Using the muslin cloth. It saves you a great deal of time.
    • Put in the coffee ground and tie the top with string to make a coffee bag.
    • When the brew is ready, lit the bag and squeeze it.
    • In this way, you can remove most of the coffee ground is before you filter through a filter. The filter will also be less likely to clog and filter faster.
Homemade Cold Brew Concentrate Ready For Enjoyment

How long can you keep cold brew in your fridge?

Usually, I finish my cold brew coffee in a week.

Filtered cold brew can last up to two weeks according to the information that I gathered from the experts and the cold brew community.

If you plan to brew a big batch, be sure you’ll be able to consume it within two weeks.


Brewing coffee is a combination of art and science.

If you prepare correctly, the flavors of cold brew are naturally sweeter and less acidic than regular coffee, so it is easy to drink as it is without sugar.

You could use the above guideline as a starting point for experimentation with your bean. After you experiment with the steeping time, grind size, and ratio of your coffee bean, you’ll know what works best for you.

It is easy to duplicate the results and consistency of the cold brew.

A cold-brewed cup of coffee prepared from excellent beans had high natural sweetness, fruity notes, medium bitterness, and a creamy texture.     

Sources: –

  1. Cordoba, N., Pataquiva, L., Osorio, C. et al. Effect of grinding, extraction time and type of coffee on the physicochemical and flavour characteristics of cold brew coffee. Sci Rep 9, 8440 (2019).
  2. Fuller, M., & Rao, N. Z. (2017). The Effect of Time, Roasting Temperature, and Grind Size on Caffeine and Chlorogenic Acid Concentrations in Cold Brew Coffee. Scientific reports7(1), 17979. https://doi.org/10.1038/s41598-017-18247-4

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