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Ice, Ice Baby: Exploring Cold Coffee

Five Senses CoffeeBen Bicknell 19 October 2015

It always amazes me how happy people are able to drink 65°C coffees while sweat rolls off them in mid-summer. However, with the increased availability and understanding of cold prep coffees, there are some really delicious options that people are turning to, allowing them to enjoy their coffee ritual without spiking the body temp.

While cold drip and cold brew are increasingly being featured in specialty cafes around Aus, you’ll often find that one cold coffee tastes like another cold coffee. As a community which is focused on specialty coffee, that is: appreciating the unique characteristics of each coffee in a culinary light, this seems somewhat regressive. In our recent Ice Ice Baby Curated Cupping, we were keen to explore and start a discussion about how we can use this refreshing, fun and approachable coffee prep method to continue our mission to celebrate the individuality of the chosen coffee.

Skip straight to the recipes!

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Cold Brew and Cold Drip

Cold brew coffee is by far the most widely used preparation method for cold coffee across the world. Simply put, it involves steeping ground coffee, commonly for around 12 hours, with room temperature or cold water for extraction. This longer contact time aims to compensate for the cool water temperature’s effectiveness as a solvent. It has often been made as a concentrate and used as an “ingredient” in preparing cold coffee drinks: imagine the classic tetrapak iced coffees. This intense brew allows the generic “coffee” flavour to hold up against milk, or in the US, half and half, and sugar. This is obviously a position we’d be keen to recalibrate — ideally the drink should be about flavour and the inherent character of the coffee vs this functional approach.

While a relatively new concept in Australia, cold brewed coffee has been around in one form or another roughly since the 1600s.

Many of the earliest records come from Japan and there are suggestions that the Dutch also explored this method to help prepare coffee which would last while on the high seas. The most highly recognised tool, almost synonymous with iced coffee around the world, is the Toddy. In 1964, chemical engineer Todd Simpson invented this simple tool to help prepare a milder coffee which his dear mum would enjoy; cold brew is often perceived as having lower acidity and bitterness, which in turn gives the impression of a sweeter overall cup.

From an international perspective, this lowering of acidity was seen as a favourable result even just a few decades ago when coffee was more commonly left on hot plates in the quintessential American diner, or in an airpot, stewing away for hours on end. With sustained heating, the chlorogenic acid in the brew would continue to degrade into quinic acid, increasing the bitter, tart experience of the cup. Considering the generally favourable role of acidity in a well brewed, balanced cup of coffee these days, especially in the Aus profile for filter coffee where juicy, bright and lively coffee really stands out, this flattening of the profile could hamper the full expression of the coffee.

The cold drip method of preparing coffee is so widely associated with Japan that it’s often referred to as “Japanese-style” or “Kyoto-style cold coffee”. Much like cold brew, cold drip uses room temp, cold or iced water which is then dripped slowly, often over 6+ hours onto a bed of coffee. Unlike the full immersion of cold brew, there is a very slow percolation process happening here. Commonly, cold drip results in a more intense, concentrated result than cold brew, with people often drawing similarities to bourbon and a certain sense of “booziness”.

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Black Tonics

A newer version of cold coffee which is rapidly gaining in popularity is the Black tonic. Purely consisting of espresso shots over tonic water, it sounds a little strange at first but as many people find, it can be surprisingly addictive. A key factor to a good Espresso & Tonic (E&T) is temperature management. Your tonic should be super cold — as close to freezing as possible — in order to maintain its carbonation. If it’s lukewarm, once the warm espresso hits it, the CO2 will quickly dissipate and you’ll be left with a flat drink.

Your next focus should be on the mixer you use as not all tonics are equal.

For those of you yet to be welcomed into the wonderfully delicious world of gin and tonics, tonic is made up of water, citric acid, flavouring, a sweetener and quinine sulphate. This last ingredient is pretty interesting as quinic acid is generally something looked unfavourably upon in coffee alone. Tonic generally has a much higher level of carbonation than something like soda and so can generally hold up to the heat addition with espresso a little more effectively. There are some great crafted tonics out there, so I’d recommend getting stuck into exploring what takes your fancy in terms of sweetness and added botanicals.

A great riff on this is using cold brew to add to the tonic — this cold coffee will help maintain the clarity of the final drink and once again preserve the refreshing carbonation.

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Nitro Coffee

This next prep method is pretty new to our shores although some of you may have sampled it around. Nitro cold brew is literally what it sounds like — cold brew coffee infused with nitrogen, a flavourless, odourless gas. The exciting thing about Nitro is the change in mouthfeel. While still avoiding milk, this coffee has a great creamy, textural mouthfeel and presents much like Guinness with its cascading bubbles. While Nitro made in this particular way (filtered cold brew then infused) achieves this, if you were to actually infuse with nitrogen while the grinds were still in the slurry, upon depressurisation, you’d actually get cavitation occurring where the gasses inside the coffee would swell, escape and allow water to rush through for increased solubility.

You can have some fun playing around with this at home with a basic cream charger and NO2 charges.

Stumptown coffee in Portland was one of the early champions of this prep method when they started serving it via tap in mid-2013. Their Nitro infused cold brew is now bottled and sold all over the US, with many other specialty roasters joining their ranks. One of the best Nitro prep setups in Aus has been put together by Tim from Coffee Keg in Geelong, VIC. With a background in micro brewing, Tim has been able to set up a large scale cold brew system that filters with non-mechanical methods: definitely worth keeping your eyes open for!

Elixir Specialty Coffee

Most of you won’t have heard of or experienced Elixir Specialty Coffee before. A relatively new beverage which is somewhat shrouded in secrecy, it’s the invention of Lee Safar, a Sydney based barista and music producer. The descriptor often used for Elixir is “Looks like whiskey, feels like tea, made from coffee“. The production method of this drink is kept top secret by Safar but the word is that it’s produced with the use of highly focused ultrasonic waves for set periods of time. This sounds pretty far out but rest assured: it’s a thing. The specialty beverage world has used equipment for a few years now which accomplishes liquid homogenisation, emulsification and things like rapid barrel aging for whiskeys. While distribution of Elixir is fairly contained at this point, only being available in Sydney and LA, if you get a chance, definitely give it a try. It’s great to see some fun innovation happening out there in the cold coffee world!

A Drop of Science

There are a couple of key concepts it’s worth keeping in mind when prepping cold brew.

Solubility
Coffee has more than 1000 chemical compounds and around 30% of coffee is actually soluble while the rest is predominantly made up of the cellulose/plant matter of the physical seed. Solubility is the ability of compounds to dissolve — our solvent in coffee’s case is water. The effectiveness of that solvent varies depending on a variety of characteristics, but it predominantly depends on heat. Each chemical compound in coffee has differing degrees of solubility — some will extract quite easily when in contact with water, while others are far less soluble and need a significant amount of help to loosen them up and get them into the brew.

Cold brew claims to hold up to two thirds less caffeine than hot brew which makes sense — given a set amount of time, caffeine extracts around 2mg/100ml at room temp while at boiling the extraction rate is 66mg/100ml. These numbers obviously change depending on things like contact time, roast level, coffee species etc, but it’s clear that it’s easier to extract caffeine at high temps. We know that coffee also has a wide range of organic acids present. On the pH scale, some tests have shown cold brew to have a pH of around 6.3 whereas hot brew has a pH of 5.5 confirming a milder acid level in the cold prep coffee.

Volatiles

Some of the solubles that coffee contains are volatile — i.e. they are able to become vapour. Volatiles are more easily released at higher temperatures (in essence, the smell is released) and this aroma component plays a big part in how we perceive the overall flavour of the cup.

Oxidisation
The oxidative process happens in a couple of ways with coffee. Lipid oxidisation occurs when the fatty acids/oils in the coffee absorb oxygen and produce peroxides, in turn creating some seriously off-putting aromas. I’m sure you’ve all smelt the inside of a hopper that hasn’t been properly cleaned and the coffee residue has thoroughly oxidised…nasty! Volatile oxidisation normally involves the aldehyde groups which present the delicious aromas of malty, sweet, caramel and, in some cases, fruit aromas like peach and pear, degrading into acid and water…a tragedy with all of those beautiful aromatics breaking apart.

Much like the other processes, oxidisation occurs a lot quicker at higher temperatures. We’ve got wins here for cold prep given our lower temp and you’ll notice that cold brew tends to hold up much better to storage than hot brew. However, we’ve also got some challenges: so much of what we perceive as taste is actually aroma. Without the opportunity for these volatiles to escape, there’s the chance our coffee will come out flat and lifeless. You’ll notice that your cold coffee has very little aroma and this is the same for any cold drink like wine or beer which is muted until it starts to warm a little. Conceptually, as you drink your cold brew, it’ll heat up and when you swallow, those volatile aromatics will drift back up your throat into your retro-nasal cavity and your olfactory sensors there. Check it out next time you’re downing a cold brew — smell it first in the cup and observe the intensity of aroma, then after taking a sip observe if you’re picking up any additional aromatics.

Cold tip:

As cold brew and cold drip require a significant amount of time to prepare, oxidisation has got ample opportunity to wreak havoc so try to keep your brews as airtight as possible once complete: this should help to maintain their best flavour.

Brewing time!

Ok so hopefully this provides a couple of useful insights into the world of cold preparation coffee out there. What we wanted to do is take this information and start a discussion about how we can all help move cold coffees into a constructive place for specialty coffee where we can continue to celebrate the uniqueness of the beans out there. During our Curated Cupping, we prepared the full line up of recipes below, but that’d result in a fair bit of coffee for you to drink, so maybe work through one at a time. Alternatively, we’ve highlighted our proposed method for cold drip and cold brew so you can skip ahead and get stuck into the good stuff. For our Curated Cupping, we used the delicious Gondo AA from Kenya but experimentation is half the fun, so pick your favourite single origin and get brewing!

We used the nifty 2ltr Toddy Cold Brew System which you can pick up from our shop, but you can also get started just using a plunger or Clever Coffee Dripper. Further cold brew tips here.

Cold Brew Recipes

Proposed
This recipe is designed to bring the origin character of the coffee back into the foreground and is what we’d put forward as the best option for cold brew. The key to the method is to reduce brew time and add in a measure of agitation.

Grind: 7 on a Marco Uber (coarse side of filter)
Coffee/Water Ratio: 80g/L
Roast level: Filter
Contact time: 6 hours
Method: Weigh and grind your coffee, remembering to rinse your filter. Place coffee in the Toddy, pour your appropriate water weight, making sure to wet all coffee evenly. Stir the coffee vigorously, 30 times around in a circle. Really get in there, making sure your paddle is going down into the sunken grounds. Cover and refrigerate for 6 hours, then filter the batch and enjoy.

Industry
This is a recipe which is pretty representative of the industry standard. A long brew time creates a strong, boozy flavour and, usually, a strong chocolaty aftertaste. Unfortunately these flavours tend to dominate any lighter aromatic qualities a coffee may possess.

Grind: 7 on a Marco Uber (coarse side of filter)
Coffee/Water Ratio: 80g/L
Roast level: Filter
Contact time: 14 hours
Method: Weigh and grind your coffee, remembering to rinse your filter. Place ground coffee in the Toddy and pour your weighed water over, making sure to wet all coffee evenly. Cover Toddy and store in fridge for 14 hours before filtering and drinking.

Experimental
This recipe comes at the problem from a different angle: we know it’s difficult to dissolve some compounds from coffee at a low temperature, particularly certain acids and volatile aromatic compounds. After our previous Curated Cupping exploring water, we wanted to explore whether we could affect the make-up of our water to compensate and help with the extraction. To make this brew water, we’re going to use Magnesium Sulphate to increase the general hardness of the water and Sodium Bicarbonate to increase the buffer. This might not be something to experiment with at home!

Grind: 6.5 on a Marco Uber (filter)
Coffee/Water Ratio: 80g/L
Roast level: Filter
Contact time: 8 hours
Method: Spike the brew water with 100ppm Magnesium Sulphate and 30ppm of Sodium Bicarbonate. Weigh and grind your coffee, remembering to rinse your filter. Place ground coffee in the Toddy and pour your weighed, spiked water over, making sure to wet all the coffee evenly. Steep in the fridge for 8 hours before filtering and tasting.

Cold Drip Recipes

Proposed
A proposed delicious recipe for cold drip — our recommended go-to! To showcase the finest elements that the coffee has to offer, we used a filter roast, increased the drip speed and fined up the grind setting. This really lightened up the generally overwhelming body, allowing some of the inherent acidity and flavours of the coffee to shine through.

Grind: 6 on a Marco Uber (filter)
Roast level: Filter
Coffee Dose: 55 grams
Direct infusion (bloom): 80 grams
Water to drip: 420 grams
Speed: 1 drip every 1 second
Contact time: ~ 2 hours
Method: Rinse your filters. Weigh and grind your coffee before shaking into the coffee chamber, making sure it’s evenly distributed. Place the coffee chamber above your carafe and evenly pour the bloom water over the grinds. Position your water chamber above the grinds and set your drip rate to 1 every second. Leave to drip through, checking on the drip rate an hour in and adjust as necessary. Using this method, we were getting ~ TDS: 3.2% – 3.6%.

Industry
While there are a million and one recipes for cold drip out there, this is fairly representative of what you’ll find. Often using older espresso roast coffee on a coarser grind setting, the drip rate is also dialled in a little slower. This recipe results in a heavy bodied, fruit and liqueur driven cold brew.

Grind: 7.5 on a Marco Uber (cupping)
Roast level: Espresso
Coffee: 55 grams
Direct infusion (bloom): 80 grams
Water to drip: 470 grams
Speed: 1 drip every 1.5 seconds
Contact time: ~ 2.5 hours
Method: Rinse your filters. Weigh and grind your coffee before shaking into the coffee chamber, making sure it’s evenly distributed. Place the coffee chamber above your carafe and evenly pour the bloom water over the grinds. Position your water chamber above the grinds and set your drip rate to 1 every 1.5 seconds. Leave to drip through, checking on the drip rate 1.5 hours in and adjust as necessary. Using this method, we were getting ~ TDS 3.10% – 3.22%.

Experimental
We were keen to explore a technique that might allow us to capture both some additional acids and volatile solubles. To do this, we used hot water to bloom the coffee. This recipe yields a different style of cold drip with a fuller profile using a hot bloom technique: similar to a filter, but with the rounded sweetness of a cold drip. At our Curated Cupping, this approach was as popular as the recipe proposed above — so definitely take it out for a spin!

Grind: 7 on a Marco Uber (coarse side of filter)
Roast level: Filter
Coffee: 55 grams
Direct infusion: 50-55 grams hot water (96°C)
Water to drip: 500 grams cold water
Speed: 1 drip every 1 second
Contact time: ~ 2 hours
Method: Rinse your filters. Weigh and grind your coffee before shaking into the coffee chamber, making sure it’s evenly distributed. Place the coffee chamber above your carafe and evenly pour the hot water bloom over the grinds. Position your water chamber above the grinds and set your drip rate to 1 every second. Leave to drip through, checking on the drip rate one hour in and adjust as necessary. Using this method, we were getting ~TDS 3.63%.

Black Tonic

Lastly, as the weather heats up, get stuck into the Black Tonics, pairing your favourite single origin or blend with chilled tonic water. For our experiments, we were using either Fever Tree or Capi, each of which brought their own flavour accents to the final drink. Make sure your tonic is as cold as possible and even add a little ice before preparing. We used 1 part espresso to 3 parts tonic water. Prepare your espresso shots and simply pull the shots directly onto the iced tonic — make sure there’s a little room in the glass: when the hot delicious espresso meets cold carbonated tonic, fizzy expansion occurs!

We hope you enjoy your cold coffee explorations! You can download both a handy all-in-one recipe sheet or our proposed Cold Brew Recipe Card for the Toddy here.

Look forward to seeing you at our next Curated Cupping, Sumatran Subregions: Welcome to the Jungle — 5:30pm, Thursday 26 November.

© Photo 1 provided with permission by Tim Williams from Tim Williams Photography. All rights reserved by photographer

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