You may have never heard of siphon coffee making. Then again, you may have read about it in the New York Times and thought it was some $20,000 gizmo used by crazy coffee nerds in San Francisco. You may have heard of it under a plethora of other names - vacpots, vacuum brewed coffee, siphon brewer, siphon vacuum coffee, and all sorts of word combinations.
This brewing method fell out of favour in the US and Canada by the 1960s, and with only a few holdovers making devices for the next few decades. Most of the major brands that used to make siphon coffee makers eased them out of production during that time, including General Electric, Silex, Sunbeam, Cory and others. Still, the brewing method maintained a hard core set of fans, maybe just in the hundreds, or dozens, and a few manufacturers continued to produce them: Bodum has continuously made a siphon coffee maker since the 1970s. Cona, out of the UK, has been making them since before World War II. Nicro, a commercial small appliances maker, was manufacturing them right up through the 1970s when demand finally disappeared, at least for cafes and restaurants.
In the late 1990s, a bunch of coffee nerds started talking up the joys of siphon coffee makers, or "vacpots", in places like alt.coffee and with the aid of rudimentary photos and pretty basic short video clips, a new (albeit small) generation of people cottoned on to this brewing method, if not for anything else than the show it provided.
And now, well into the first decade of the 21rst century, and some 160 years after the siphon coffee maker was first invented in France and Germany, the technique is set to explode (figuratively, not literally) with almost everyone in the specialty industry taking interest. Peter Guiliano, the famed green bean buyer for Counter Culture Coffee and acknowledged as one of the best cuppers in the business today, lists the siphon coffee method as one of his favourite ways to make coffee.
Back in 1998, I saw my first ever siphon coffee maker in action. I make no joke about this - it was a seminal moment for me in coffee. I was very much into all things espresso at the time, and I still recall the first time I brewed a cup. I'd been reading about vacpots for a few years - mostly in the newsgroup alt.coffee, but also in books like Ken Davids' Joy of Coffee - but it wasn't until I stumbled upon a used Bodum Santos in a flea market that I bought one, took it home and set it up for the first brew.
Almost everything about using a vacuum coffee maker is sensory involved: aromas, fragrance, motion, touch, action. Grind the coffee, add it to the top vessel. Add cold (or hot) water to the bottom. Put the bottom on a heat source. Add the top vessel with its attached siphon. Watch. Liquids defy gravity. The brew gurgles, but it's not boiling. Remove from heat source. Watch the coffee move back down, or "south". Watch the bottom vessel's brewed coffee gurgle as air is drawn through the spent grounds to release the built up vacuum. Remove top vessel. Smell. Ahhh. Pour. Taste. More ahhhh.
So much science. So much sensory involvement. So much fun. And the taste. Do it right, and you'll wonder not at the fact that so many specialty industry leaders consider this "the best".
How Do Siphon Coffee Makers Work
A vacuum coffee maker works on the principle of expansion and contraction of gases - actually one gas, water vapour - is what allows the device to brew a full infusion style of coffee and filter the grounds efficiently, leaving a generally clean, pristine cup.
Siphon coffee makers are made up of four parts: the bottom container where the water initially sits and the brewed coffee eventually rests; a top container that has a siphon tube attached to it (and a hole in the bottom of the vessel), where the coffee brewing takes place; a type of sealing material (usually a rubber gasket) to help create a partial vacuum in the lower vessel while brewing is taking place, and a filter, which can be made of glass, paper, metal, or cloth.
There is also a heating source, and there's usually three types - a cloth-wick alcohol burner (slowest), gas or electric stovetop (faster), or a specialty butane burner (fastest). There are additional heating devices, including the halogen burner system that is part of the $20,000 setup that Blue Bottle Cafe in San Francisco has for their siphon coffee makers.
Once the siphon coffee maker is assembled, heat is applied to the lower container. As it heats up, some of the water is converted to a gas - water vapour. A gas occupies a lot more space than its liquid or solid variant, and it can expand as more heat is applied. Gas can be compressed, but only to a point, whereas liquids do not compress. The water vapour continues to expand and it seeks some relief from all the compression it's starting to have.
The only escape route out of the bottom vessel is the siphon tube traveling up to the top, but the problem is, there's a lot of liquid blocking its way. So what does the gas vapour do? It pushes the water up the siphon tube!
This is how the brewing water "defies gravity" and gets up top past the installed filter and starts saturating the coffee grounds. Heated (though not boiling) water will continue to force itself up the siphon tube until the vapour gas in the bottom vessel can have direct access to the siphon. By design, all vacuum coffee makers do not have siphons that sit flush with the bottom vessel: there's always a couple of millimetres of clearance (or more). This leaves some water in the bottom vessel which serves two purposes - protects the glass (if it boiled dry, glass would superheat and could crack), and has a continuing source of water to turn into - you guessed it - more steam, vapour, gas!
This is a desirable thing. Once the water in the bottom vessel is lower than the siphon tube, water vapour starts pouring up the siphon into the top chamber. This does two things - it keeps the liquid all up in the top vessel where the full-saturation brewing is taking place, and it continually heats the top vessel, maintaining near-ideal brewing temperatures (90C and 95C (185F and 204F)). As the vapour bubbles pass through the top liquid, it may appear that the active brewing is "boiling" but in fact it isn't under normal brewing conditions. If you leave the siphon coffee maker long enough, eventually the top vessel water temperatures will reach 100C, but this takes a very hot heat source and five or more minutes of brewing time in most cases.
Once the brewing time is completed (different sized siphon coffee makers require different brewing times), the heat source is removed and more simple physics take over. Remember that gases expand when heated and that gases also compress under pressure. When heat is removed, the gases start to contract and shrink. Eventually all the gas in the bottom vessel contracts enough that it starts to create a partial vacuum of pressure (negative pressure), and it start pulling the brewed coffee back down, through the filter.
Another thing is going on as well - phase change. Some of the gas vapour starts changing back into its liquid form: water. This is almost like a miniscule turbo boost for the contraction of gas and vacuum forming, aiding the pull of the brewed liquid back down to the bottom vessel. At first it starts slowly, but as you watch, things will pick up speed and unless the coffee filter has been excessively clogged, the last half of the water travel down south will happen twice as fast as the first half did.
The effect is so efficient that once all the liquid has passed back down to the bottom vessel, air is drawn through the grounds up top, drying them out, to fill the vacuum void in the bottom vessel and balance out the pressure to normal room atmospheric pressure. For some, this is how the siphon coffee maker got one of its names - the ground coffee is literally "vacuumed" dry.
How to Use a Siphon Coffee Maker
Enough preamble - here's the reason you're reading the article - the visual how-to. This is our preferred method for using a siphon coffee maker, but it is by no means the only way to brew with these devices. In fact, there's plenty of debate online today by people who have newly discovered these devices, and how different things like stirring techniques, steep times, and even the use of cold vs. preheated water can affect the taste. Some of these theories and practices are interesting to try out, while others seem like a bit of fluffery with no real effect on the cup at best, and a detrimental effect on the cup at the worst.
The most important things to note about using a siphon coffee maker are a) using fresh roasted, fresh ground coffee; b) grinding just before brewing (no wait time in between - so grinding is one of the things you do last); and c) maintaining and monitoring heat during the brew.
You don't need expensive equipment to make vacuum brewed coffee at home. I do just fine with a $30 Yama 5 cup stovetop model (that includes a nice cloth filter and five spare cloths) as I do with my $150 Hario Nouveau and my $50 butane burner. In this how to, I'm using one of the smallest siphon coffee makers I own - the two cup (8 ounces) Yama "Classic" model. In fact, this is the first time I've ever used this particular vacuum coffee maker, part of my collection of over 50 models.
After the visual how-to, We'll provide some information on the variety of filters available, starting points on how much coffee to use, how long to brew, and how to super-tweak your vacuum brewed coffee experience to get an even better taste for your taste buds.