If you've ever experienced a weak and watery brew when using a very dark roasted coffee, the hot bloom method may help. The large amount of surface oils on dark roasted coffee, due to the extended roasting process, can make it difficult for water to fully wet the coffee bed during the brew cycle. There's nothing more frustrating than seeing sections of the coffee bed that are completely dry!
We've found that the "hot bloom" method can help you get a fully saturated coffee bed and an even extraction when using these dark roasts.
As demonstrated in the video above, you're simply pouring about 2 ounces of hot water (just off boiling) onto the coffee bed. This allows the subsequent dripping cold water to fully saturate the coffee bed and properly extract a cold brew.
Not sure if you need to do a hot bloom with your coffee? Simply sprinkle a teaspoon of the ground coffee onto the surface of some cold water. If a dry pile just sits on the surface, you need to do a hot bloom. If after 30 seconds, the coffee grounds begin to sink and are completely wetted, there's no need for the hot bloom.
In the above photo, I've sprinkled a very dark roast onto two cups of water. One contains hot water and the other cold. This illustrates how the hot water has the ability to saturate the oily surface of the coffee grounds while simply using cold water does not.
Water's surface tension is at play here. Water molecules have cohesive forces that bind them to one another. For the water molecules on the surface, these cohesive forces are stronger. Rather than seep into small spaces, the water has a tendency to bridge the gaps as a result of surface tension. Any surface oils on the ground coffee further exacerbate this issue. As water increases in temperature, its surface tension decreases significantly. This allows the water to flow into tiny crevices rather than bridging the gaps leaving them dry.
From the testing we've done, we haven't noticed any significant changes in flavor when doing the hot bloom (still the smooth, low acidity brew that we've come to love). Since we're using such a small amount of hot water, it's really just saturating the bed. It's still the cold water and a whole lot of time that's doing the majority of cold brew extraction.
If you ever experience dry grounds, give it a try and let us know how it works for you!
Lately, I've been thinking a lot about acidity, its connection to coffee, and cold brew in particular. Acidity is what gives coffee its liveliness. Without acids, coffee falls flat on the tongue. However, It's also the thing that many people point to as the culprit of their upset stomachs. We love cold brew for its silky smooth texture and naturally sweet taste, but many also seek it out for its lower acidity.
In The Coffee Roaster's Companion, Scott Rao discusses the changes in a coffee's acidity over the course of the roasting process. Multiple organic acids contribute to acidity, and a large part of a coffee's acidity and bitterness comes from Chlorogenic acid. During the roasting process, the Chlorogenic acid breaks down into quinic and caffeic acids. These acids contribute to the mouthfeel and "brightness" of the coffee. Citric acid imparts a sourness while Malic contributes a more clean flavor to the coffee.
He writes that organic acid development peaks around light roasts, and gradually decreases as the roast continues. As an experiment, I wanted to see how the total acidity compared between cold brew made from the same coffee roasted to different degrees.
For the experiment, I chose an Ethiopian blend of green coffee from the green coffee importer Sweet Maria's. I wanted to look at the two extremes of the roasting spectrum, so I roasted the light roast to the middle of first crack, and the dark roast to the middle of second crack. These had drop temps and roast times of of 203º C / 9 min and 223º C / 16 min respectively.
The difference in roast levels are pretty stark in the above picture. Both cups contain 60g of coffee, but the dark roast is obviously less dense. The light roast also has more chaff (the husk on the coffee seed). This is due to having spent less time in the roaster resulting in less mechanical agitation that would have removed it.
Brew Water pH: 8.12
A little about the pH scale before we look at the results. The pH scale goes from 0-14, and 7 is considered neutral. pH levels below 7 are considered acidic, and above it are considered basic.The scale is also logarithmic. That means that for every 1 unit change in the pH, there's a ten fold change in acidity. For example, a pH of 6 is 10 times more acidic than something with a pH of 7.
The brew water I used for both experiments had a pH of 8.12. This was definitely more on the basic side, and likely the result of our ground water having a lot of mineral content.
The light roast with a pH of 4.89 was over 10 times more acidic than the dark roast with a pH of 5.96.
As expected, there was a very noticeable difference in taste between the two. The light roast had a distinct brightness to it that began at the front of the tongue and went back with a very light body. Reminded me a lot of the acidity in diluted lemon juice. The dark roast was a completely different experience from the light roast. Nearly all of the brightness from the light roast was gone, and the taste was much rounder with a significantly heavier body.
It was interesting to see the correlation between acidity and roast level corroborated in this experiment. My personal preference would have been for a roast a little darker than the light roast to round out the acidity just a tad. For those looking for a less acidic brew, going with a darker roast will definitely reduce the overall acidity. For those that want a livelier brew, opt on the lighter roasted side.
From when we first came up with the concept of Cold Bruer back in early 2013, there's been at least 20 iterations on the design. Some changes were little tweaks here and there, others were much bigger. Most occurred in the months leading up to the launch of our Kickstarter campaign back in 2013.
While Cold Bruer has been out in the wild for more than a year, the iterative design process hasn't stopped. We've been continually working to make Cold Bruer even better, and this Summer, we're excited to roll out an updated design!
Our original intention behind the design of Cold Bruer was to create a slow drip cold brewer for the home user. We wanted it to be compact, durable, and easy to use, and this is still the driving force behind our most recent changes.
The most obvious change is the removal of the handle and the necking in on the carafe. By removing the handle, we were able to reduce the amount of space Cold Bruer takes up on your counter and in your refrigerator. An added benefit was the increased durability of the carafe since there was no more fragile handle sticking out.
We added measurement markings for both the coffee and water chambers to approximate 60g and 700ml of water. These will come in handy if the batteries in your digital scale die, and your measuring cups are MIA.
We're pretty excited about the new lid design! The original lid we designed for Cold Bruer was intended to fulfill the two functions of covering the tower during brewing, and creating an airtight seal on the Carafe. However, having to allow air to vent into the tower, but seal in the Carafe meant that it had to be loose fitting on the Tower. It did it's job, but it just didn't feel quite right. By making the lids two parts that snap together, we were able to get a good fit on the tower and an airtight seal on the Carafe.
We've increased the glass thickness to increase durability. Compared to our original Cold Bruer, this feels more like holding a pint glass than a wine glass!
With many hot brewing methods, it is common to wet the ground coffee (often referred to as"blooming") with just enough water to saturate the grounds and let it sit for a short period of time. This helps prepare the coffee bed for a more even extraction by releasing trapped CO2 gas and wetting all of the ground coffee so that it can undergo a more uniform extraction.
We recommend doing the same when setting up Cold Bruer. However, we've typically only done the pre-wet with cold water... When it comes to Cold Brewing, the idea of doing a "Hot Bloom", using hot water for the pre-wet followed by cold water for the rest of the brew, has been around for a while. There's a good article describing the method written by Lorenzo Perkins of Cuvee Coffee Here a few years back.
Essentially, the idea of using a hot bloom is to release easily dissolvable volatile compounds that produce the fruity and floral qualities to the brewed coffee that cold water alone may not extract entirely. With this in mind, we gave it a go!
We used about 25ml of water at a temperature of 205 degrees F. The first thing we noticed was the ground coffee wet very evenly and a TON of tiny CO2 bubbles formed between the ground coffee particles much faster than when we pre-wet with cold water. We let the coffee bloom for about 10 minutes before inserting the valve and adding the remaining ice water to the tower.
We set up another Cold Bruer with all the same variables, but we used cold water (about 50 degrees F) for a comparison. With them side by side, it's pretty cool to see how much more CO2 is initially released from the coffee causing the coffee bed in the Hot Bloom Cold Bruer to expand a lot more than the "Cold Bloom".
We were really surprised by the differences between the two! We used Temple Coffee Roaster's Ethiopian Boke that's already pretty fruity with a nice amount of acidity. The hot bloom method produced a cold brew that definitely heightened those fruity flavors and brought out a little more acidity in the cup. We're looking forward to doing some more hot bloom experiments! Give it a shot and let us know what you think!
As these Winter days get shorter and the temperatures drop, we wanted to share our method for making hot cold brewed coffee with Cold Bruer. Sometimes, on these chilly mornings, theres no substitute for a hot cup in your hand, and for that less acidic brew, cold brewing is a great way to go.
There's a few methods to heat up your cold brew.
Microwave....Stovetop...Simply adding hot water
The microwave is certainly the fastest, but I've never had great results with it. Seems like my cup of cold brew is always boiling before I know it, and it tastes a little off after that...
The stovetop is good if you want to heat up a bunch of cold brew, but has the drawback of dirtying extra dishes.
My favorite method has been to brew up a concentrate and then add boiling hot water to bring it up to temp and get the right dilution. To get the concentrate, I'll simply add half the water that I would normally use to brew. In this case, the ratio of coffee to water by weight is 1:6 (our normal is 1:12).
Getting specific on the numbers:
I'd found that this produces a concentrate that is good to be diluted with an equal part hot water to get the right strength. Diluting the coffee with an equal part hot water also brings the temperature down to about 135 ºF. A great drinking temperature.
If the cold brew is coming out of a refrigerator, the final temperature will be on the cool side, so in this case, I preheat the cup by pre-heating it with hot water for a minute before pouring it out and adding in the cold brew and hot water. This technique gets the final brew temp right where I want it.
Desperate for a caffeine fix, we've done it. The result was an overpoweringly strong brew. Nothing like the smooth, sweet brew we're accustom to. In this post, we'll take a closer look at the various stages of extraction and do a little taste testing while we're at it.
You may have noticed that those first initial drips into the carafe are super dark while the last few drips are much lighter in color and more transparent. The rate of extraction is not constant. Looking at the picture above, it doesn't even appear to be a linear process. It looks like the bulk of extraction has taken place during the initial parts of the brew based how dark and opaque the first sample is compared to the next sample.
This sort of non-linear extraction is expected. In "Everything but Espresso" Scott Rao explains that coffee extraction occurs in two stages. In the first stage, water contacts the grounds and quickly washes away most of the exposed solids on the surface of the coffee grounds. The second stage occurs much slower and involves the bean fibers absorbing water. Over time, the dissolved solids migrate out to the surface to be washed away.
We set things up using our standard cold brew recipe:
We decided we'd divide up the batch into 4 separate samples, so I marked a line on the carafe indicating 150ml (the coffee absorbs about 100ml). Once the cold brew reached that line, we'd pour off that sample to keep them all separate. This short timelapse shows the process.
In order to not completely overwhelm my taste buds, I tasted the least extracted stage first. That's the one on the right shown in the picture above marked 4/4. This sample was the 4th quarter ( and last) stage of the brew. I then sampled the third stage of the brew and so on...
I filtered about 10ml of each sample into separate cups and then measured the percentage of total dissolved solids (TDS) of each. For reference, our target brew strength is typically about 2% TDS. I began measuring the last stage and least extracted sample first. By the third sample (the second stage of the brew) it was clear that the trend was not going to be linear. I was expecting the first stage of the brew to have a much higher TDS, but it was out or range of my refractometer (measures 0.00%-5.00%). To try to get it in range and estimate the original % TDS, I diluted it with 1 part distilled water. This brought it down to 2.63%, so I estimate the original was about 5.26%.
To get an idea of what the average TDS of the brew would have been had I not separated the samples, I mixed equal amounts of each sample and measured the % TDS to be 1.95%. Very close to our target of 2%.
Like all good experiments, this one's brought up more unanswered questions.
Could I brew a half batch in half the time and just dilute the concentrate with water?
Suppose I diluted that first stage to a brew strength of the combined average (1.95%). How would it taste? In other words, what flavors do the last stages of the brew contribute?
Could I brew with a finer grind over a shorter period of time and reduce the risk of over extraction?
How fast can you brew? Are there any benefits to much longer brew times?
These are some good questions we often get and they have to do with the overall brew strength and extraction of the cold brewed coffee. In a previous blog post found here, we looked at the influence the grind size had on the brew strength and extraction. In this experiment, we're going to look at how the drip rate (and resulting brew time) will affect the brew strength.
The drip rate is definitely an important variable with Cold Bruer. From our development phase of the product, we know that there's a limit to how fast you can brew. Otherwise, patience aside, we'd likely be tempted to make a pot of cold brew in 6 minutes rather than 6 hours.
From our experience, we suggest brew times of around 5-6 hours for a proper extraction. In this experiment, we're going to look at brew times on both sides of this recommendation and see how it has impacted the extraction. For this experiment, we're going to look at 3-hour, 6-hour, 12-hour and 24-hour brews.
Coffee: Medium roast Kenyan from Artis (about 4 weeks after roast, so not super fresh).
Brew Water: 700ml ice/water (300g ice and 400g water)
Grind: Medium drip (7-F on Baratza Vario)
At a starting drip rate of about 1 second between drips, our brews take about 6 hours to finish. Based on this, we set the drip rate on the 3-hour brew to about 0.5 seconds between drips. For the 12-hour and 24-hour brews, we set the drip rates to 2 and 4 seconds between drips respectively.
It was pretty fun to watch them progress at different rates, and each appeared to be on track. Our 3-hour brew ended up taking a bit longer. A little over 4 hours. The 12-hour brew finished while I was asleep, but it looked like it was still on track to finish in time as I went to bed. The 6-hour and 24-hour brews finished on schedule.
Once the 24-hour brew finished the following day, we grabbed some people from our shared office space to taste the results. With a few differing opinions, most everyone had similar tasting notes about the cold brews. Our 24-hour brew tasted flat and tanic with a pretty unpleasant bitterness that lingered. The 12-hour brew had high initial acidity, and then went flat quickly. The crowd favorite was the 6-hour brew that most everyone found to be the smoothest and sweetest. The 3-hour brew had similar sweetness as the 6-hour brew, but it lacked the body, and tasted a little thin and watery.
After the qualitative tasting, we brought out the coffee refractometer to measure the brew strength for some quantitative data. The total dissolved solids (TDS) were measures as follows:
You can't rush a good thing! There's a certain amount of time required to make great cold brew, but too much time is not a good thing either. I'm curious what the results of the 3-hour brew would have been had the brew actually taken 3 hours to complete (definitely more on the thin/watery side). It was a bit surprising to see the drastic difference in taste between the 12-hour and 24-hour brews given that the brew strengths differed by only 0.04%. This makes me think there's something else at play than just the extraction...
Fizzy cold brewed coffee? There's a few commercial cold brewed coffees emerging on the on market, and we thought carbonating some cold brew of our own could be an interesting experiment. Anyone that's drank soda that's gone flat knows what a significant role carbonation plays in how it tastes. Bringing that added ZING to cold brew could be a welcomed addition to an already refreshing beverage.
You can carbonate just about anything. Seriously. Even ice-cream! On top of that, there's numerous ways to carbonate. Carbonation is the process of dissolving carbon dioxide (CO2) gas into a liquid. To do this, an air-tight container with liquid is pressurized with carbon dioxide, and the pressure forces the carbon dioxide to dissolve into the liquid. When the container is opened (de-pressurized) the dissolved CO2 comes out of solution forming bubbles and creates the fizz we're familiar with.
The two primary methods to carbonate are:
Forced carbonation Set-up
In forced carbonation shown above, CO2 is supplied by a highly pressurized cylinder containing the gas. This is the method I use when carbonating my home brewed beer, and it's the method used by the popular sodastream soda maker. Unfortunately, it's a bit equipment intensive...
Natural Carbonation Set-up
In natural carbonation, yeast is introduced to the liquid. As these microorganisms converts the fermentable sugars in the liquid, CO2 is produced as a byproduct. Alcohol is another byproduct. However, due to the relatively short fermentation time required to carbonate, you can expect less than 1% alcohol content.
Natural carbonation requires very little in the way of equipment (as shown in the picture above), so we're going to use this method to carbonate our cold brew in this experiment. I've adapted the below recipe from a really great book on making home-made sodas called True Brews. The recipe can be found here.
What you need:
Champagne yeast can be found at your local home brew supply stores or here on Amazon. The amount required is minuscule for a 16oz batch. It's a little difficult to measure if you don't have a gram scale and I don't think 1/32 sized measuring teaspoons are even made, but just a pinch of it between your fingers should be about right. Also, champagne yeast is chosen for it's taste neutrality.
White granular sugar is used to give the yeast something to ferment. The amount you use will influence the final sweetness of the carbonated cold brew.
Step 1. Add the cold brew to the yeast and sugar in the bottle. Leave about 1 inch of headspace at the top.
Step 2. Seal container and shake!
Step 3. Leave in warm location for 12-48 hours.
After some time, you'll notice the increasing pressure in the bottle when you try to squeeze the sides. The firmness is a good gauge of how carbonated your cold brew will be. Once it's nice and firm, you can put it in the refrigerator to stop the fermentation process and prevent it from over carbonating.
After about 18 hours, our bottle had become firm to the squeeze, so we opened it up and poured ourselves a cup of cold brew. Compared to a soda, It was lightly carbonated, which gave it an interesting effervescent mouth feel. Very different from the cold brew we're used to drinking.
That fizzy-ness definitely gave it more of a bite. That smooth, less acidic taste we're familiar with seemed to be supplanted by the carbonation. In this batch, we definitely noticed the added sweetness from the sugar. It was a little too sweet for my tastes, and I'd try using less sugar in the next batch, or I'd let it ferment longer (at the risk of over-carbonating).
This makes for a super easy way to experiment with carbonated cold brew. I'd recommend trying it out. It's definitely not how i'd like to drink cold brew every day, but I could see it being a nice change once in a while. It could be interesting to start adding some other ingredients so that the cold brewed coffee is playing a more supporting role. Maybe something alcoholic? What ever it is, I'd probably leave the milk out of it though.
Let us know how your experiments turn out!
It's not every day that you get to brew up the same coffee that's been roasted to three different levels, and we were excited for this opportunity when Artis Coffee gave us 3 bags of a Kenyan coffee each roasted to a different final temperature.
Roasting coffee is a process where green coffee beans undergo a chemical and physical transformation as they are heated up. The ultimate temperature a coffee is roasted to can have an enormous impact on the flavor of brewed coffee.
The unique origin character, those particular flavors that identify the location the coffee is from, begins to be overshadowed by the flavor of the roast as the roast progresses. Some classic origin flavors for a Kenyan you can expect are bright acidity and citrus notes. Light roasted coffee will have more origin flavor, and they will become muted or nonexistent in darker roasted coffee.
There's certainly more to the roasting process than the final temperature the beans are brought to that will influence the final product, but temperature is a great variable for comparison. Most coffee roasters spend a great deal of time roasting samples of a particular coffee to different temperatures and roast profiles until they've found the profile that they feel maximizes the favor qualities they are trying to highlight. Similarly, Artis does this with many of their coffees, but they also give the customer the option to have their batch of coffee roasted differently. They roast to order using small fluid-bed roasters (seen in the upper right picture). This affords an unprecedented amount of experimentation for the consumer.In the above picture are the three Kenyan coffees from left to right roasted to 396 ˚F, 400 ˚F and 405 ˚F. there's a slight change in the bean color visible, and you'll notice that the 405 ˚F roast is beginning to secrete some surface oils.More noticeable is the difference in density of each once they are ground. 60 grams of each coffee was weighed out, but, it's clear that the lighter roast takes up less volume in the glass while the darker roast takes up more. This is do to the continued release of water moisture as the roast progresses.Brewing parameters
We pulled in people from our shared office space for a blind cupping of the coffees. To taste the coffee, we used the traditional technique of "slurping" the coffee from a spoon so that it covers your palate all at once. Surprisingly, by doing this with each coffee, I was getting really intense sensations that reminded my of inhaling hot chocolate powder mix. It was a bit overpowering, so I went back to politely sipping it.
The majority's favorite was the middle roast that was the most balanced of the three , but some people preferred the light roast, and others the dark roast. I personally leaned towards the light roast. I really enjoyed the refreshing quality that the citrus flavors added along with the higher levels of acidity.
Come taste it with us!
Andy and I will be tasting samples of the different roasts at Artis Coffee in Berkeley, Ca this Friday, July 25th from 2-3PM, and we'd love for you to join us!
1717 4th Street, Suite B
Berkeley CA 94710
One of the coolest things about being involved in a Kickstarter project is the alternative uses of your project that community members come up with.
Could I use Cold Bruer for...
Cold brew tea?
Looking back, the latter seems like a pretty obvious application, but being pretty devout coffee addicts, tea wasn't something we'd given a whole lot of thought too. While exhibiting Cold Bruer at the SCAA show in Seattle, we were given a handful of Stash Tea to try out in Cold Bruer. It was a perfect opportunity to begin some tea experiments.
For our first cold brewed tea attempt, we used Stash Tea's Estate Premium Iced Tea: It's a blend of black teas with oil of bergamot. I chose a brewing ratio of about 1 to 24, so we used about 30 grams of Stash's Black Iced Tea Blend, and 710ml (24oz) of ice/water. I've seen some loose leaf teas that have pretty large pieces of tea leaves, but this stuff looked very similar to the typical coffee grind setting we use for our cold brews. I wonder how important the tea particle size is to the brew...
I'd read about iced tea brewing ratios ranging anywhere from 1:60 to 1:24. I chose the more concentrated ratio because I was concerned that water could easily channel right through such a thin tea bed and leave it under extracted.30 grams of tea doesn't look like very much at all in the tower, but after doing a pre-wet of 15ml of water, and setting the drip rate at about 1 drip per second, the tea bed swelled more than I expected and doubled in volume.The brew finished 5 or 6 hours after we started, and I was really surprised at how dark the cold brewed tea was. To show dow dark it was, there's a mug of cold brew coffee on the left, and the mug of tea on the right.
Initially, we drank the cold brewed iced tea just over ice. It was definitely concentrated, and the oil of bergamot reminded me a lot of Earl Grey. It was strong. A little too strong for a refreshing summer drink, so we ended up diluting it with about 1/3 water. A little dilution, and a squeeze of lemon made for a very refreshing iced tea!
These very encouraging results definitely warrant some additional experiments. I'm curious what the slow drip cold brewing method can bring to iced tea that other iced tea brewing methods can't (full-immersion seems to by the most prevalent method out there). I'm particularly interested in how the various brewing methods will influence the tannin content of the brew that gives that dry/astringent taste that is characteristic of black tea.
If you've thought about brewing iced tea with Cold Bruer, give it a go! We love the endless creativity of the Cold Bruer community, and would love for you to share your experiments with us. #BruerBlog @bruercoffee
Botanical tinctures or alcoholic infusions for the next blog experiment? Perhaps. But you can bet there will be some side-by-side comparisons of iced tea brewing methods in the future!