This brewing method is called siphon brewer, or a vacuum brewer or vacpot. It produces a complex yet smooth and mild cup of coffee which is coveted by coffee aficionados worldwide.
We strongly encourage you to read through the Expert’s Guide to Siphon Brewing if this is your first time attempting siphon coffee brewing.
Please note the guide below uses a Halogen Light Beam Heater, but other heat sources are interchangeable. Common heat sources include butane burners and de-natured alcohol burners. For more information on types of heat sources, please see the Expert’s Guide below.
There are two chambers for water which are connected by a siphon that goes through a filter. The bottom chamber - which is used to heat the water - is positioned over a heat source of some kind (a stove, an open flame from a butane gas or alcohol burner, or a halogen light beam). A stand is used to hold the bottom chamber upright on the counter. The top chamber is open on the top end and contains the siphon which protrudes into the bowl of the bottom chamber. In between sits a filter, usually comprising a metal or plastic filter holder, a paper or re-usable cloth filter, and a tension spring to hold the assembly firmly in place. Finally, there is a sealant that sits between the two chambers in order to create a vacuum; usually this is a rubber gasket that is held into place on the upper chamber.
Water is filled into the bottom chamber (see the markings along the side of the bowl for measuring how much water to portion). The filter is set into place on the top chamber, which is then carefully secured into the bottom chamber. When the heat source is turned on, the water in the lower chamber begins to rise in temperature. During this process, two important things happen. As water reaches its boiling point, the liquid water molecules turn into gaseous molecules: water vapor. And since the gaseous form of any liquid takes up more volume than its liquid version, the bottom chamber is put under pressure to expand. The only place for movement comes from the siphon that protrudes into the bottom chamber. However, the expanding gas cannot access this escape since all the remaining water is blocking the way. So the resulting force pushes the water through the siphon, past the filter, and into the top chamber.
You will notice that the siphon tube doesn’t reach the very bottom of the bottom chamber; this is by design. This ensures that there will always be some water present in the bottom chamber and prevents the glass from superheating and cracking. Another important reason is to provide a constant source for water vapor and therefore pressure to push the hot water upwards into the upper chamber.
When the heat is removed from the bottom chamber, the entire process reverses. The temperature in the bottom chamber lowers, and the water vapor returns to its liquid form (which takes up less volume). This changes the pressure difference between the two chambers. Now there is a force pulling the liquid from the top chamber back down into the bottom chamber. It is from this action that the name “vacuum brewer” or “vacpot” was coined.
Coffee and Water
Always use freshly-roasted whole-bean coffee that is kept in an air-tight container away from sunlight or changes in temperature or humidity. Freezers and fridges are not suitable for storage as they are great places for odor and flavor cross-contamination.
- Grind Size
There is no set rules for grind size for siphon brewing, rather the grind size is directly linked to the type of filter your brewer is equipped with.
For cloth filters, a fine to medium-fine grind is recommended.
For paper filters, a medium-fine to medium grind is recommended.
For all-metal mesh or glass filters, medium to medium-coarse grind is recommended.
Less expensive blade grinders produce uneven extraction and bitter coffee. We highly recommend using a good grinder.
- Coffee Amount
- There are two different ways to measure the amount of coffee to use, either by mass or by volume. We recommend measuring by mass, because different roast levels will lead to difference in bean densities, which impacts how much coffee is used when measuring by volume only.
- We recommend using 7 grams per fluid ounce of water (30ml).
For example, a “3-cup” Siphon (which is 12oz or 360ml) would require about 20 grams of coffee.
1.7g x 12oz = 20.4g
Since a cup of coffee contains about 98 percent of water, always use filtered water boiled fresh each time. Water that is continuously boiling or re-boiled will start to taste stale and may have rancid odors. If your water does not taste great, neither will your coffee.
- Heat Source
There are several different types of heat sources that you can use to heat your siphon.
- Stove Top – If your siphon’s bottom chamber is flat on the bottom, then it is designed to sit on top of your stove. This makes it easy to select your heat source.
- Alcohol Burner – This type of burner is challenging to use as it does not give consistent or powerful heat. The flame intensity can vary, depending on the nature of the environment: drafts, open windows, or large rooms will make consistent heat difficult to achieve. Also, some kinds of alcohol give off soot while burning. Choose a de-natured alcohol, ethyl, or an ethyl/isopropyl mixture that has high ethanol content. They burn hotter and do not give off as much soot as others.
- Butane Burner – This kind of gas burner, when equipped with an open/close type valve, is a good investment. The radial valve allows you to control the rate of gas flow (and therefore the intensity and temperature of the flame). The flame also has sufficient force so that it is relatively consistent and has a quick response time in changing temperature. This kind of burner is recommended.
- Halogen Light Burner –This type of burner uses a bright halogen light to heat the water. The radial dial on the front allows fine-tuning of the light’s intensity (and therefore its flame temperature and intensity This type of burner is highly recommended despite its pricing as a main drawback.
We recommend having a count-up or programmable count-down timer that shows minutes and seconds so you can track your extraction time properly.
- Stirring Instrument
You will need something to stir with. Glass or metal are not recommended due to the possible scratching or cracking of the glass brewer. We recommend a good-quality plastic paddle, bamboo paddle, or wooden spoon. Be sure to rinse and wash your stirrer well as it will most likely absorb coffee oils and flavors.
- Siphon Filter Material
Cloth filters permit all of the coffee’s essential oils through and into your cup; however, it is more difficult to keep clean. Throughly rinsing and drying after each use is, therefore, important as old coffee oils trapped inside the filter will turn rancid and negatively impact each successive cup you brew.
Paper filters restrict some of the coffee oils and coffee solids from passing through into your cup, but are always clean and will not retain any off or spoiled coffee odors.
All-metal mesh or glass rod filters permit oils through, but also a larger proportion of coffee solids. Your cup will resemble that of a French Press-brewed coffee.
We are able to recommend each type of filter, according to your use and needs.
- Siphon Body Style
Different shapes or designs of siphon brewers have no distinct advantages. Instead, the quality of the glass is the most important quality to look for when buying a siphon.
- Serving Vessel
Ideally, a cup of Siphon-brewed coffee should be served in a thick-walled ceramic mug that has been pre-heated. Glass cups are also acceptable, but be careful of high temperature, as they will get very hot when you pour in your coffee. Plastic cups, thin-walled ceramics or china, or paper cups allow heat transfer far too easily and you will find yourself sipping cold coffee in a relatively short time.