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Rethinking Iced Coffee - Part 2 - Cold Brew
8/3/2013

By: Christian Ott

I left you off in my last blog with some things to think about with brewing – primarily, what we like to refer to as the six essential elements of brewing.  If you haven’t read that blog, I suggest that you read through briefly – because a lot of the science that I discussed there will be relevant in the Cold Brew conversation. 

(You can click here to read the previous blog.)

Cold Brew 

At Stone Creek Coffee, we love our Cold Brew.  He even have it on tap at our Factory and Bay View stores.  This special form of iced coffee makes a sweet, rich, and fruity beverage.  It also tends to not be bitter.  However, if you think about brewing in general, several elements of brewing are not necessarily “right” when doing cold brew.  For example, we use cold to room temperature water to make cold brew.  But, to get the best extraction of coffee, you need to use 195-205F water.  Another element is brewing time: most coffee brews quickly (2-5 minutes, depending on brew method).  Cold brew often takes between 12-20 hours, depending on method.  However, it still tastes good!  What’s going on here?

Adjusting the Brew Method

Brewing is all about ratios and holding constant variables.  For example, I enjoy my drip coffee best at 2g per fluid ounce.  I then find the grind that works with that coffee at that ratio. I keep the temperature (195-205F) constant.  I also look for a relatively stable time of extraction.  Those variables are tethered to that ratio.  When brewing hot coffee, those variables are relatively static.  When we drop the temperature of the brew water over 130 degrees F, we need to make some corresponding adjustments.  

Have you ever brewed coffee with water that was not quite hot enough?  It probably tasted weak, yet not overtly bad.  This is because the cooler water can dissolve some of the coffee grounds, but not as much as hot water.  If you measured the percentage solution, it would be very, very weak (remember, ideal brew strength is between 1.15 and 1.35% solution).  This tells us that we have to compensate via grind or brew ratio somehow – and we need to make the solution stronger.  Fining the grind could accomplish this, but due to the cold water, it wouldn’t necessarily make a difference, since we can’t dissolve as much out.  However, if you add extra coffee (we call this updosing), you can actually dissolve more into the solution.  When creating cold brew, you typically use a much higher ratio of coffee to water (for the Mizudashi, 100g per 1L (3g:1oz ratio) – for Toddy, 340g of coffee to 56oz of water (6g:1oz ratio).

Therefore, if we are using more coffee, we have to keep a few other elements in mind.  First, the coffee must become saturated with water before it releases its flavor elements.  Agitation is imperative, especially when brewing large amounts of cold brew.  When creating this year’s cold brew, it was randomly weak and watery.  After a lot of experimentation, I found out the cause of this was due to the grounds not actually saturated.  We can accomplish this saturation easily if we use a coarser grind (less surface area means that water can move evenly between the particles.)  WE also want to make sure that we do not over-extract the coffee as well – and the larger the particle, the longer it will take to extract.  

Science of Cold Brew Extraction     

Why is cold brew so delicious?  Above, I alluded to the fact that coffee with cold water does not extract everything out of the grounds – yet cold brew tastes like a “full” cup of coffee.       

In the past, I’ve heard of people enjoying cold brew because it was less acidic.  To the contrary, citric (think citrus fruits) and malic (think green apples and grapes) acids are fully extracted, even with cool water.  This is what contributes to the fruity flavor of coffee – and arguably, what makes coffee so flavorful to begin with.  Sucrose is also extracted in full proportions, which gives cold brew a rich sweetness.  (Acid also increases the perceived sweetness of coffee.  Believe it or not, acid is GOOD!)

So, what isn’t extracted at this lower temperature?  First, we see lower amounts of chlorogenic acid, the most common acid found in coffee.  Though we call it an acid, this is one of the primary contributions towards making coffee bitter.  Less chlorogenic acid = less bitter. 

Interesting side note when you don’t use enough coffee in your batch brewer, often this coffee tastes bitter – this is due again to an increase in chlorogenic acid, which is one of the elements extracted in higher concentration towards the end of a brew cycle.  If your coffee tastes bitter, think about how we compensate with cold brew, and INCREASE the amount of coffee grounds that you use. 

Fatty acids are also not extracted at a high concentration at colder temperatures.  Bitter and salty flavors love fat (this is why salt on French fries tastes so good).  When you remove the fat, the perception of the salty and bitter flavors decrease.  I am willing to wager that your cold brew will never be bitter – it might be strong – but never bitter, due to this fact.

How to Brew

The other great thing about cold brew is that you really don’t need a ton of equipment to make it.  If you have a French Press at home, or even a large plastic container (like this), you’re set.  I’ve even heard of people using a coffee filter, a mesh strainer, and a large bowl (similar to this).   

Here’s my basic ratio for cold brew:

Large vessel (like Toddy): 6g per 1oz of water, use room temperature water, coarse grind, let steep for 12-15 hours.  (This brew method makes a “concentrate” of sorts – meaning, you can dilute if you choose).

Mizudashi: 100g per liter, grind medium, let steep with room temperature water for 12-15 hours.      

Coffee to use:  Start with your favorite coffee.  I also recommend Cold Brew Blend, Black Sheep Blend, and the Ethiopia Yirgacheffe Konga.  

Next Blog: Part 3 – Bypass Iced Coffee and Cold Brew Mods

Sources:

"Iced Coffee" from Beans and Water (blog) by Lorenzo Perkins


 





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