UNFILTERED: Our first 24 hour steep trial used a French Press in place of a filter and resulted in cold brew that very full bodied, with a bitter, almost oily texture. While this may be favorable for some palates, it doesn't agree with most drinkers, especially during hot summer afternoons.
PRE-INFUSED & UNFILTERED: For the next trial we pre-infused the coffee grounds by boiling about 10% of the total water and pouring it over the grounds for 30 seconds before adding the rest of the room temperature water, again in a French Press. Pre-infusing cut down on a good deal of bitterness and oil (though some still remained) and resulted in very full bodied coffee with a smokiness and light acidity.
FILTERED: The third taste test had us placing ground coffee inside large paper filters which were tied into what looked like a giant Hersey’s Kiss. For this trial we choose to forgo pre-infusing the grounds to see how much of an impact filtration would have on the end result. After 24 hours the end product had much less body, dominated by a stronger acidity.
FILTERED & PRE-INFUSED: For our final 24 hour steep test we combined the previous filtered brewing set-up with the pre-infusing technique. This last method was easily the favorite of all the 24 hour steep methods, as it produced a coffee with a full body, lively acidity and retained more of the complex flavor profile of hot coffee.
The secret to Japanese iced coffee’s success lies in its combination of hot extraction and quick cooling. In the Japanese method half of the typical water weight for the brew is replaced with ice inside the brewing vessel while the other half is just off the boil and then poured over medium to finely ground coffee and through a filter.
One of the primarily limitations of 24 hour steep cold brew methods is that despite the vastly increased brew time, cold water cannot dissolve as much of the ground coffee’s soluble solids as hot. We tried to get around this limitation with the pre-infusing technique mentioned above, but this proved only a partial solution. If we were to try to create iced coffee with the same complexity as hot brewed simply by refrigerating after hot coffee brewing, we run into the same problem with bitterness previously mentioned. However, by having the grounds bloom in water just off the boil, then immediately drip down into ice the Japanese method avoids this problem by quick cooling the coffee and locking in aromatics and flavors so they don’t evaporate into the air.
In addition our variation on the Japanese method (which you can find here) only takes about 3-4 minutes to brew, making it the clear winner in flavor, simplicity, and convenience.