The most important thing when preparing coffee, is the recipe. Cold brew is no exception to this rule, even though we tend to think that steeping time is flexible. To a certain extent, it is a bit more flexible than hot brew recipes, but you still need to be careful.
The advice on how long to steep cold brew varies, and there is some advice from experts, but never explained. So I wanted to find out what is the optimal brew time for cold brew, especially that I disagreed with the general consensus on the matter. So I set up an experiment which told me what is the best steeping time for cold brew.
Learn in this article what is the ideal steeping time for immersion cold brew, for perfect extraction and for maximum caffeine extraction. This is a deep dive into the brewing process, and if you need just a recipe, we have two articles that are just that:
- How to Make Cold Brew in a French Press – the most frugal way to make cold brew
- Easy Way To Make Cold Brew Coffee In A Mason Jar – easy cheap and convenient
I only evaluated immersion cold brew in this experiment. Dutch cold brew has different extraction time, and vacuum brew method needs only a few minutes for the extraction process.
Why The Experiment?
If you look at my Quora profile, you’ll see that I don’t follow trends, and I question the advice in the industry. It was only normal to question the common wisdom. At the end of the day, there is a lot of misinformation on the Internet, including cold coffee brewing.
The brew time for cold press is something that bothered me, because when cold brew first started, the recommended steeping time was 36 hours, up to 72 hours. And in time the advice changed and got to 9 to 12 hours. That is a big change…
To be honest, I haven’t made immersion cold brew in a long time, so before the experiment, I didn’t even remember how immersion cold brew coffee tasted. I brew at home, but my favorite method now is vacuum cold brew, which is really fast, and it is delicious.
But I still wanted to have an answer for my readers, since I got this question quite a few times: Is it fine to cold brew for extended periods of time? and what is the best steeping time for immersion cold brew?
You see, I had an idea on what to expect. Before the experiment, I was convinced that cold brew doesn’t over-extract, however, I kept an open mind about it. Especially that there is some research which suggested I was wrong in my assumption.
My theory, before the experiment, was that if we steep really long times, we just need to dilute more.
Let’s see if I was right about it, and let’s see what is the perfect extraction time for immersion cold brew. But before the experiment, let’s dive deeper into immersion cold brew as a method of coffee preparation.
Overview of the Cold Brew Process
Immersion cold brew is a process of extracting coffee using cold water instead of hot water. It results in a different taste profile compared to traditional hot coffee, described as sweeter, less bitter, and smoother. There are various ways to prepare cold brew, such as cold drip, vacuum cold brew, agitation, but immersion is the most popular brewing method because of the low tech and low cost.
The basic procedure involves combining ground coffee beans and water in a specific ratio (usually ranging from 4:1 to 10:1 by weight). The mixture is then left to steep for a period of time, typically 12 to 18 hours in the refrigerator.
The steeping time can vary based on personal taste and the longer the brew sits, the stronger the coffee will be. After steeping, the coffee grounds are filtered out, and the finished brew can be enjoyed cold, to prepare iced coffee, or warm it up for a unique experience.
Importance of steeping time in cold brew making
Steeping time is an important factor in making cold brew coffee. Extraction time at room temperature is shorter than steep time in the refrigerator, as cold water slows down the steeping process. This is due to different solubility depending on the solvent temperature.
However, steeping the cold brew in the refrigerator results in a cold drink after the steep time is up, while cold brew made at room temperature still needs to be chilled. Chilled coffee needs less ice cubes when preparing a cold brew iced coffee.
A general consensus is that a steeping time of at least 12 hours in room temperature water gives the best results for the majority of people.
This also allows for brewing the coffee the evening before and having it ready for the next day. On the other hand, it is believed that a batch of cold brew extracted for 18 hours is better, as this gives the water sufficient time to create a full flavor. 12 hours steep time is the most popular recipe, since it fits perfectly in most peoples daily routine. You can prepare a batch in the evening, and you have it ready for the next morning.
Under Extraction and Over Extraction
Roasted coffee is a mix of various compounds soluble and insoluble. The soluble stuff makes up to 30% of the total content. Out of this 30% soluble content, about 8% is undesirable extract, stuff that make our coffee taste bad.
For hot brewed coffee, the ideal extraction is between 18 and 22%, depending on preference, brewing method, and the coffee beans. Above 22%, we have an over extraction. Over-extracted coffee tastes bitter, tannic, and overly strong. Under 18%, we have under-extracted coffee, which tastes weak and sour.
The beauty with coffee, is that the bad tasting compounds are less soluble, so they extract later in the brewing process. So knowing exactly when to stop brewing, ensures a perfect cup.
But is this valid with cold brew as well? Maybe the bad tasting components in coffee are soluble only at higher temperatures…
Let’s see what my experiment revealed.
The Experiment Setup
I prepared 7 batches of cold brew, that were extracted for: 12 hours, 16 hours, 24 hours, 36 hours and 72 hours. The 12 hours batch was a set of three batches with different grind sizes: Coarse grind, medium coarse grind, and medium grind size.
I used 50 grams of ground coffee per mason jar. The mason jar has 500 ml, but measuring the ratio of coffee to grounds is by weight. The actual coffee to water ratio was 1:6. Which translates into 50 grams of ground coffee and 300 grams of water.
I let the coffee steep as per the setup for 12, 16, 24, 36, and 72 hours. I stopped the brewing for the short steep batches by sequentially removing the ground coffee from the mason jar, and storing the cold brew concentrate in the fridge, until all the batches were ready.
When all the batches were ready, we tasted all of the cold brew concentrate jars, undiluted for a first impression. Then we measured the TDS of all jars, and we diluted the the concentrate to normalize it to 2.00% TDS.
We then tasted the coffee again.
Coffee that was extracted for shorter times tasted better. We could distinguish subtle flavors and notes, specific to cold brew.
The longer the steeping time, the more bitter and tannic the coffee tasted, regardless of the concentration. So much so that the 72 hours was almost unpalatable.
The three 12 hours batches tasted differently, with the finer grind tasting better than the coarse grind.
The 16 hours batch was a very close replica of the 12 hours batch, so don’t try too hard for perfect time.
The TDS difference between the subsequent batches was not huge, but the taste difference was night and day.
|Brewing Time||Grind Size||TDS||Taste|
The last column is a numerical representation of the flavor, on a scale of 1 to 10, with 10 being the best tasting cup, and 1 the worst tasting one.
As you can see from the table above, the best tasting coffee was steeped for 18 hours and less. The longer we steeped the coffee after the 18 hours mark, the more bitterness we extracted.
The interesting part of the experiment is the grind size. While this was a secondary test, it is almost as important as the brew time experiment. While the steep time confirmed the industry recommendations at 10 to 18 hours brew time, the grind size experiment did not. Almost every recipe we found recommends a coarse grind size. Our taste test showed that the finer grinds gave us a more flavorful cup, compared to the coarser grind which was flatter.
After dilution, we normalized the TDS to 2%. The taste scores did not change, although the bitterness was not as prevalent as with the concentrate.
It looks like the sweet spot is between 10 and 18 hours, depending on your preference. Going over the 24 hours will deteriorate the taste in more than one way.
Firstly, we will extract unwanted compounds that give your coffee a bitter taste.
Secondly, these unwanted compounds will start to react with the polyphenols and other antioxidants in your coffee, destroying them.
There is definitely no advantage to steep cold brew for more than 24 hours, in fact it is detrimental to your coffee cup quality.
Diluting the cold brew concentrate does not change the flavor profile, it merely tones down the bitterness of the long steeped coffee, but it still tastes worse than the short time steeping counterparts.
It would be interesting to test lower brewing times, and different roasts. For instance, compare light and medium roasts with a darker roast. I am also interested to test in the future a medium grind with short brewing times, such as 3 to 10 hours. Maybe strain the brew through a paper filter, similarly to slow drip.
I hope that this experiment sheds some light on the steeping time for cold brew. I know there is so much more to learn about it, such as different extraction times and different grind sizes, but you have now a good reference.
Don’t steep for more than 18 hours, or else your coffee will start to degrade.