Okay it's nothing like the labs I used to work at, but the thought of using scientific equipment in my kitchen makes me squee. The range of possible food preparation uses for such gear is pretty endless, but right now this is what I'm using to make coffee.
A bit of history.
This all started a year or two back when Ondine discovered Funranium Labs and their Black Blood of the Earth. This was very cool. I had played around in the past with overclocking my brain using various commercially available preparations (aka Jolt Cola, Redeye, Red Bull), so I knew where Herr Direktor Funranium was coming from. BBotE is a crazy product and it's actually kind of hard to produce, due to the sort of gear required to make it.
Then, there was the trip to Melbourne last year where we discovered Japanese siphon coffee and the bunch of guys there playing around with Viennese extractions. There are some really potent and interesting caffeinated beverages being experimented with in Australia right now.
Enter the cold extraction method - other wise known as cold brewing. Ondine and I both have a scientific background, and I encouraged her to purchase glassware in the name of science. The first product she was making was good, but I could see a few ways to improve on it. Enter several more purchases. Several boxes of glassware, a magnetic stirrer and a whole bunch of buzzed out people that tested "the product" for her.
The principle is astoundingly simple and it's rather amazing that most people are unaware you can even do this. First take fresh ground coffee. Immerse in cold water for a reasonable period of time. Filter. Drink. Okay there's a bunch of variables here that radically change the end product, but the fact remains, the coffee taste components are extractable in water, as is the caffeine. Where this technique differs from drip filtering or any process involving heat, is that heat changes the oils, extracts acids from the beans and can change the flavour. That really nasty cup of espresso you get at the local that leaves your lips tingling - their water is too hot or they are over extracting. It's almost impossible to over extract with cold brewing because you don't cook the beans.
Remove the heat this and your coffee seems a lot less oily and it never tastes particularly bitter. You don't get as many other side effects either such as upset stomach or teeth staining. It also means you can produce as much as you like in one session and store it. The reduction in bitterness also means you don't need to use sugar or milk, making it diabetic friendly.
This is how I am currently doing it and it works for me. Other people on the interwebs do it other ways, and the important thing to remember no way is best - use different produce and you will get a different result.
First start with a container. I use a 1L Schott bottle. The glass is Pyrex borosilicate, and this kind of bottle is superior for this kind of thing. Ondine is a shift worker and makes her coffee on a much large scale in a 5L Erlenmeyer flask. The larger the volume the more agitation required to get the grounds to infuse, so she has also moved to a magnetic stirrer. This is probably a bit overkill for most people, but you cannot argue with the results.
Next chose your coffee wisely. Not all coffee tastes the same when infused cold. To me espresso roasts taste pretty bad. I'm currently using Yahava's Black Gold blend as I feel it retains a lot of the cappuccino machine flavours when extracted. It also has a fruitiness, not dissimilar to green apple or peach. A big plus for me is Yahava has their Swan Valley operation literally 5 minutes drive away, so I don't need to buy in bulk. I can get it fresh any time.
The grind of the coffee also makes a big difference. A fine grind results in a faster extraction and more flavours - including the nasty ones. It also makes the end filtering more difficult. Filtering as you will see is the main headache with this method. Lately I've been experimenting with a relatively coarse grind to good results.
The next variable is the quantity of coffee. How much, and how much water? I find a ratio of 1:5 coffee to water is a good starting point because only so much can be dissolved in a given solution and still be workable. You could add more coffee, but you will find that coffee is surprisingly light and takes up a lot of volume. 75g occupies around 100-150ml of space until you add the water and I'm not convinced you get a much stronger extract by increasing more to the mix. I start with 75g of ground coffee to 500ml deionised, distilled or filtered water.
The water. There is the argument that tap water is better because it adds flavour. I say if you are happy to drink your tap water go for it, but here in Perth the water often tastes like it's come from a swimming pool, or sulphurous when they are have been using ground water. Filtered water is probably the best thing to use here.
Measure out your coffee and your water. Mix, (preferably in your chosen container) and then let it infuse. For your first extraction, 24 hours at room temperature is sufficient. You don't get a huge benefit from going longer than this, the caveat being temperature!
Let it rest.
Like a lot of things science, temperature is really important. More caffeine and flavour is extracted at 30c than at 15c, but at higher temperature bugs grow best, the brew deteriorates as the delicate flavour molecules break down and your extract starts to go off. Unless you want to risk ruining your batch you really want to keep things clean and work in the low to medium temperature range. I have had good results using a 12-18 hour extraction at room temperature (22-28c) and then refrigerate for another 12-18 hours before filtering. By good results I mean good strong clean taste and a fair kick.
How to make it drinkable? Well the next step is to filter out the muck. Ondine and I have found that cotton make up pads (don't laugh) actually work really well. They are close to being sterile, and have a loose enough weave that they can catch a lot of sediment but retain high flow rates when just using gravity. If you do chose to use these, buy the cheapest ones possible. The more expensive ones are usually doped with perfume, and trust me, flowery smelling coffee is not good.
I have attempted using a Büchner funnel and vacuum pump apparatus to produce a nearly dry filtered ground, but there have been a few shortfalls in the gear I acquired on the cheap. The vacuum is not perfect and standard filter paper easily blocks. As mentioned above a coarser grind really will help you clean up the extract. Fine grinds leave a sediment that takes a long time to settle and gets everywhere.
When you have poured out the contents of the bottle, you can attempt to rinse the grounds and get a little more extract. This will give you slightly more volume, but in my experience adding more water will leach out bitter compounds and also dilutes what you have collected.
You have your first cold brewed coffee. It may be slightly cloudy depending on the filter you used or the grind but this normally will not impact the taste. Try it. If you like it, you can drink it straight, add hot water and/or milk. You can also use it as a base for cooking, or make a great coffee sauce for icecream. The average bottle of coffee will keep for up to two weeks in the fridge, but you can also freeze it. Like anything with food, lower temperatures and cleaner equipment means you will get a better shelf life.
|Final Extract. The Black Oil|
If you do want to want to clean up your extract further, I recommend letting it settle in the fridge for 3-4 hours, and then pouring it through a clean filter. Like wine sediment, letting the liquid settle will result in a better result, without you having to resort to using more expensive filtration methods. A light oil slick on the surface is also perfectly normal and a sign that you have extracted oils out of the grounds.
Now, if you are ambitious and want to make something a little stronger, you can try extracting additional fresh coffee using your first volume as the liquid phase. You may need to add a little more liquid as you go because on a ratio 0f 1:5, it's quite likely you have lost up to 100ml during the first round of processing. Subsequent extractions will get stronger and stronger, but the end result may not be as pleasant to drink.
Now I unleash you, go forth and make potent drinks.
Author's warning: Caffeine is a powerful stimulant with nasty, potentially life threatening effects in large doses. Be responsible with this stuff. Glassware used here can be obtained through companies such as Perth Scientific. If you do decide to buy on eBay, please make sure it's "new" gear. Second hand equipment may have been exposed to all kinds of nasty chemicals that will leave you with bad hangovers or worse.