Double Dipping on Ice Brew Coffee

So Iced Coffee (and Cold Brew, and Toddy Coffee) have been getting a lot of traction these past few weeks; all started with that great instigator Peter Giuliano who hopefully will be writing a followup soon.

I’ve been experimenting off and on with cold brewing coffee since about 1998, when I bought my first toddy brewer. But I have to be brutally honest here: cold coffee (or espresso) is not about super culinary delights in taste exploration for me like espresso is, or siphon brewing is, or press pot or even drip brewing is. Cold coffee (or espresso) is purely about a pleasing taste and something cold and refreshing. So I have had no qualms about adding both a sweetener and milk to the beverage. Sugar especially, since the well known scientific fact that sweets are perceived less the colder a beverage is.

Back in 2009, I did some heavy experimenting with an aeropress for cold brewing. My reason for testing wasn’t so much about the aeropress as a cold brewing device, but to test something I knew to be true (as my tastebuds told me) regarding cold espresso methods: when brewing espresso for using in a cold drink, I found the resulting beverage much more pleasing and rounded (and soft, even) if I chilled the espresso in stages instead of shocking it to cold by brewing it directly onto ice. To this day, espresso tastes a bit metallic and sharp if I brew it directly onto ice.

I didn’t find the same thing in brewed coffee (ie, brewing onto ice), but never really tested it. So I did a series of experiments with an aeropress to produce a cold cup of coffee: I’d brew it directly onto ice; brew it into cold water then add ice; and brew it traditionally, then add it to a second chilled vessel, then add some cold water, then finally some ice.

I didn’t find much discernible taste difference once I figured out the water ratios on these experiments (that took a bit of time). Well, that’s not entirely true: I actually thought one cup I brewed doing a two stage chill (brew into cold water, add ice) tasted slightly better than the other methods, then I found out that I had screwed up my water/ice/coffee brew / grounds used ratios (I know…). I adjusted the other ratios for the other brew methods and found all the cups produced tasted better, and pretty much even.

Looking back on it now, I realised I may have been able to preserve more of that particular coffee’s best taste notes with the adjustment, but I didn’t realise that at the time. So a few days ago I decided to try a new experiment, and this one was purely based on stuff I read from Giuliano. I worked on both my grind fineness and dosing parameters for doing a Chemex brew with a Kone filter, right onto ice. I also worked on two other things - one very controversial, one not so much.

Safe Stuff

I found that by going to a much finer grind, and by using a bit more coffee (8g/100g water/ice) and fooling around with my pouring method quite a bit, I was able to coax some real individual flavours out of the coffee I as using for this experiment - a Colombia from PT’s Coffee. That’s the not-so-controversial part.

Controversial Stuff

I also tried something else - something that is probably real heresy in the world of coffee and espresso (and it is, since I’ve done my part to make it heresy). I would pour brewed coffee back through the coffee grounds, essentially double-dipping my brew. Gasp.

Before I get to the results, there is some method to my madness. Passing 200+F water through a bed of coffee once is enough to take a lot of the good stuff (and some of the bad stuff) out of that ground coffee and put it into your brew. Passing super-hot coffee brew through a partially (or mostly) spent bed of coffee will only really extract crappy bitter stuff you don’t want in your cup. This is why percolator coffee tastes so horrible.

But reducing the temperature of the water used to brew, during the brew cycle, has some interesting effects. You can try this yourself and pretty easily: boil your brewing water in a kettle; wait until that water measures around 202F (use a meat thermometer, you don’t need anything fancy or have to be exact), and start doing a slow pourover brew. As you pour, your water is cooling - cooling inside the kettle, and cooling as it passes through air to the bed of coffee. But to kick things up a bit, keep pouring higher and higher (while remaining safe) as you do the pourover - the longer passage through the air will reduce the water temperature even more. Pour slowly and a thin stream. Try tasting this brew next to a brew you poured close to the bed of coffee, but everything else is equal.

When I did my “double down” experiments, I had to have some starting blocks, so I set up this ideal:

• 400g of ice in the chemex
• 100g of water to be absorbed by the bed of coffee (my initial bloom steep - first water I poured into the bed of coffee)
• 400g of water to be poured through the bed of coffee
• roughly 800g of liquid resulting (once ice melts - bed of coffee will retain at least 100g of water)
• Then take half that volume of brew, and re-pour it (cold) through the bed of nearly-spent grounds

My logic behind this was multifold:

• According to all research I’ve read, the lower the “brewing water” (or brewed coffee, in this case) temperature, the less perceived bitters will be extracted. Others can give you the exact scientific names for this chemical and that fat and this lipid and that element that is particularly affected, I’ll just state: colder the water, less bitters (and acid) extracted.
• Using 80g of coffee but only pouring 400g (500g) of hot water through it means there’s still a lot of solubles and non solubles to extract
• The brew I poured through would not reheat the bed of coffee, but would in fact cool it down more.

Why only pour half the coffee through the bed again? I don’t have any scientific reasons other than my goal was to ultimately pour 600g (700g) of liquid through the bed. I could pour more or less, but this is where I started.

So what were the results? Surprising, promising, but not definitive. I need to experiment with this more. Would encourage you to do the same. Here’s what I got, and I had two friends and my spouse Beata be taste test bunnies as well.

I poured about 100g of the “brewed once” coffee into a cup, and poured about 100g of the “brewed twice” liquor into another cup. Then I added all the remaining 600g of coffee (300g double brewed, 300g single brewed) into a separate vessel and served 100g of that.

The Brewed Once liquor was had the best perceived sweetness, but no distinguishable flavours other than “coffee” flavours for my tasters and me. I could taste some acidity but it was soft and mellow. No one else tasted that.

The Brewed Twice liquor had less perceived sweetness, but still wasn’t unpleasant for any of the tasters. That said, one taster and Beata both noticed what they called “a soft fruit taste”. This Colombian we used from PT’s Coffee has good stone fruit tastes when brewed hot - particularly apricot and peach. I’d call this a serious win for the brewed twice method for this particular coffee. In my case, I couldn’t taste any real fruit I’d notice, but since I was aware of the stone fruit tastes from the hot brewed coffee, I kind of perceived it - not definite though. I did not the sweetness was mellowed out, but not at any perception of excessive bitters. The coffee just seemed more complex to me.

The Mixed Brew liquor really did have a balance of both prior examples - a bit more sweetness than the brewed twice on its own, and one taster felt she could notice a bit of fruit character. All four of us liked the mixed brew the best out of the three samples.

This was not very scientific and I certainly didn’t follow any real rules of taste sampling, like blind tasting or double blind. I was using a 2g accurate scale, and not entirely getting every number accurate - call it pretty informal. But the results were enough for me to really look a bit more into double-brewing for cold coffee brewing - first time around the ice coffee brew method (or as Peter Giuliano calls it, Japanese method), second time around pouring cold brew coffee back through the bed again. Try it yourself and see what happens!