Cold Drip Coffee vs Ice Brew Coffee, which one is more you?

Posted by Dave Lim on

 

Introduction

 

Our sister companies Sun Ray Cafe and Parchmen & Co have been offering ice drip coffee for about two years using MyDutch coffee maker. We wrote this article to explain the broad differences between cold brew and ice drip. We have done an experiment to validate our theories and beliefs, and consolidated these findings in this article.

Characteristics of the two coffees

Before ice drip became popular, most coffee shops were using the cold brew method, this is mostly due to the perceived belief of the ease of batch brewing. We wanted to better understand the strength of each method and the recipe to make a tasty ice drip coffee.

Towards this end, we did our study in two steps, to answer these two separate questions. Throughout our study, we used Sun Ray Cafe's shop grinder Ditting KR804.

The coffee used is Ethiopia Guji, medium roasted three days ago, has a limey and almondy note on the dry fragrance, translating to a juicy berry juice when tasted. (Note that the coffee has higher propensity to produce a sour taste than a bitter taste.) The dripper was the MyDutch M350 (350 ml). The cold brew apparatus was a 350 ml container. Cold water was used throughout the experiment. Once each set of coffee was done, they are bottled, capped and chilled until ready for tasting.

In the first step, we made two coffees per set, one using cold brew and one using ice drip, maintaining the extraction time per set and varying only the drip rate for the ice drip, at 1 drop every second or two times slower at 1 drop every 2 seconds. The grind size per set is the same. The dosage is at 40 gm. This is best presented in a table:

Observations and Deductions

We made the following common observations across the two methods:

  1. Grind size: A finer grind extracted harsher flavours of saltiness and bitterness. A coarser grind extracted more sweetness but a weaker taste, and was drying on the tongue. Coarser grind allowed a wider spectrum of flavours - from green grassiness to almond cheese.
  2. Extraction time: Longer time, i.e. slower drip rate or longer infusion time, produced a more 'dusty' coffee - less sweet, less sour, more bitter.

On the comparison of the two methods, we made the following observations:

  1. Brew by infusion: Coffee colour is brownish, tasted more rounder and oily, with a long aftertaste. However, it tasted diluted throughout all samples.
  2. Ice drip: Coffee colour is black, but set 3's drip coffee is lighter in colour than the rest. Coffee is generally richer in taste, but edging towards off-balance, and has a short aftertaste.

Deductions:

  1. Cold water extracted coffee following principles of hot water extraction. The strength of the coffee can be improved by either a finer grind size or longer extraction time (i.e. a slower drip rate or longer infusion time). This is the reason of the lighter colour for set 3's ice drip. We confirmed that it was indeed a weak coffee by tasting it against the other sets. In fact, it was the weakest coffee amongst all the coffee. This is mainly because it has the lowest surface area of extraction (being the coarser grind), and that the contact time between water and medium was the shortest (being the coffee with the shorter extraction time).
  2. A slower drip rate translated to higher extraction due to the prolonged time from start to end of making the coffee. The longer time gap between drips allowed more flavours to be dissolved into the retained water in the coffee bed. In other words, there was more contact time between the medium (water) and the ingredient (coffee grounds), thus allowing higher extraction. The subsequent drip not only carried the heightened flavours of this retained water in the bed, but also maintained the wetness of the bed for another round of higher extraction to be absorbed by the next drip.
  3. Cold brew allowed coffee oils to be extracted whereas ice drip has a fine filter that cleaned up the coffee. Coffee oils smoothened the coffee and rounded up the sharp tastes in the cold brew.
  4. Ice drip is more economical in cost and time. For the same dosage, ice drip coffee produced a stronger taste as compared to cold brew, thus making it more economical to produce commercially or at home. Further, it took a shorter time to produce a strong coffee using the ice drip method, as compared to the cold brew, thus making it more time-economical as well.

Finding a perfect ice drip recipe

We recognised the potential of the ice drip and worked towards perfecting a recipe. Although ice drip coffee is always being recognised as a strong coffee that is "thicker" than cold brew (for the same amount of coffee used), its taste could be too sharp for greater acceptance by the general public. This could work against our goal of introducing real and fine coffees to the wider population who are already accustomed to commercial sweet coffees that comes with syrups, cream and crushed ice. To work on this weakness, we concluded that it was due to the lack of coffee oils in ice drip.

To make a smoother coffee

As such, we decided to make Adjustment 1: To remove the filter at the bottom of the coffee basket. The result was a smoother coffee no less. However, there were coffee grounds that fell through the perforated coffee basket.

We made Adjustment 2: To tamp the coffee so as to compact it to reduce the amount of loose grounds that could dislodge from the basket. Indeed, the coffee became physically cleaner. But most importantly, the taste became more refined and focused.

The surprising taste outcome of Adjustment 2 intrigued us. We related this finding back to coffee extraction theory that when coffee is tamped, the quality of contact improved because the free space in between the grounds that the water molecules can navigate is reduced and compressed, and there is higher extraction per vertical distance travelled downwards. This also means that the "drain rate", i.e. the rate which the extracting water drains through the coffee bed, is slower. This is despite that the vertical distance in the coffee bed the water travels is shorter as compared to another untamped coffee bed. The drip rate must also slow down to match the reduced drain rate, so as to prevent a case of "flooding" in the coffee basket. This ties in with Deduction D2 above, as the extraction is now prolonged, and the quality of extraction has increased, thus improving its overall quality.

To produce a longer "aftertaste"

Aftertaste can be generally understood as a combination of the retronasal aroma, and the remaining taste after the coffee is swallowed. According to this definition, calling 'aftertaste' that, is in fact a misnomer, as it consists not just taste but also aroma; and taste and aroma are what form flavour. AS such, it will be more accurate to name it 'after-flavour', which consists of aftertaste and retronasal aroma ("after-aroma").

A good aftertaste should not be disturbing - overly bitter or overly sour, any of which will cause imbalance to the coffee. The retronasal aroma should be pleasant and lasting. This has two broad categories:

  1. Enzymatic aromas: Characterised by green, vegetal notes, usually indicative of under-extraction, and the retronasal aroma is more reserved and focused at the front of the nose. Coffee insiders may like this aroma.
  2. Sugar browning aromas: Characterised by roasted notes, usually indicative of over-extraction, and the retronasal aroma is more forthcoming and unrestrained at the top and back of the nose. General public recognises this aroma as coffee.

We were trying to understand the longer retronasal aroma produced by the infusion method, and concluded that it was a direct outcome of over-extraction. To create this effect, we made Adjustment 3: To increase the dosage from 40 gm to 50 gm, and to increase the water travelling distance. This also led to the increase in the ratio from 1 : 8.75 (40 gm coffee to 350 ml water) to 1 : 7 (50 gm coffee to 350 ml water). This produced a coffee with a more lasting aftertaste, although it inevitably led to an half hour extra in extraction time and a sharper taste. To balance the stronger flavour, Adjustment 4 saw the grind size increased from 5.5 to 6. Finally, after all these adjustments, the ice drip coffee is strong and smooth, with a long aftertaste.

Drain Rate

This has effect on the quality of extraction in two manners, both relating to the intimacy of contact between the extracting water and the coffee grounds:

1.

(Furthermore, the extraction would be uneven throughout the coffee bed, with more extraction on top. This happens because the water was "light" and unsaturated at the start, thus promoting higher extraction rates. By the time the water travelled to the bottom of the coffee basket, it would already be "heavy" and saturated with coffee compounds, thus limiting the extraction rate. But the water would still extract, with the molecularly lighter and more fruity (sour) coffee compounds still dissolving into the water. As such, there would always be a case of over-extraction at the top and under-extraction at the bottom. The water travelling halfway through the basket is bitter from the over-extraction, and get flavoured by fruity (acidic/sour) compounds from the remaining coffee grounds at the bottom of the basket. This produces a coffee which is bitter and sour at the same time, creating an off-balanced taste. We also noted that the bitter note at the back of our tongue has disappeared, and we concluded that the under-extracted compounds that included malic acids components (which is bitter) has been suppressed or balanced off.

Ice Drip Recipe

The general recipe for the MyDutch M350 is summarised in the pictorial below. We will be sharing this recipe during our Caffeine! coffee appreciation workshop.

Subsequent research

We will test out this recipe for a nutty or chocolatey coffee, which will be roasted darker. Stay tuned.

We also verified that the flavours of the ice drip coffee takes one day to consolidate and it could taste a bit diluted immediately after dripping. This profile can sustain for another two more days before it starts to decline. As such, finish your ice drip coffee within two days!

Happy brewing! Enjoy your fine coffee!