Ada’s Coffee Hacking: Siphon Brewing
Siphon style brewers have been around since the mid-1800’s and, although they were more complex than other methods, they gained popularity in the Victorian era in Europe and more recently a following in Japan. Different variants were invented, but they all primarily worked by heating water in one vessel (the vacuum flask, with a heat source underneath) which then moved to the brewing chamber to mix with the coffee grounds once it was heated above boiling (or when the vapor pressure exceeded the atmospheric pressure). Once you were done brewing the coffee, you would then cool the vacuum flask to create negative pressure which would suck the coffee back through the filter and could then be served. With balance siphon brewers like the one pictured in fig.1, this whole process was mechanically automated since once the water moved to the brewing flask, it would automatically put out the lamp and begin the cooling process. With tower siphons on the other hand (as seen in fig.2), you would have to manually remove from the heat to begin the drawdown process.
Both of these methods result in a brew similar to other immersion methods (french press, aeropress, clever, etc), but because vacuum pressure is involved, you’re able to more heavily filter and dry the grounds than with other immersion methods.
Our co-owner, David, has been personally fascinated with this brewing method for a while and he’s thinking of how we could make use of it in our store. However, the main issue cafes run into with siphon brewing is with brewing consistency. The amount of time for water to boil into the brewing flask can vary wildly. And the brew water temperature can vary drastically as well. David built a few different prototypes for automating this process with a infrared thermocouple and PID controlled heat-lamp, but he wasn’t satisfied with any of the results. We could definitely brew coffee that tasted fine, but not consistently and fool-proof enough for us to be able to precisely dial-in our recipes and reproduce them in a way consistent with our cafe’s service standards.
After months of tinkering, David decided to scrap everything and go back to the drawing board. The primary benefit of the siphon was to do immersion brewing with vacuum pressure based filtration, so looking at this from a modern lab perspective, the equipment you would use would be something like a filter flask, which pretty closely resembles the vacuum siphons of yesteryear. From this idea, he found a vacuum flask that we could attach a standard siphon top-piece to and built a base that integrates with the Acaia bluetooth scale and contains a vacuum pump that can initiate the drawdown process.
David also built out software that allows us to consistently reproduce recipes by automatically starting timers when water is poured, visualize pour speeds in a way we can easily reproduce, and engage the vacuum pump at a specific time during the process to begin filtration. One side effect of using a vacuum pump is that we can now do things like add additional filters if we want more clarity and vary the vacuum pressure to precisely control the speed of the draw down. Also, by introducing the water to the grounds in the top piece, we’re able to precisely control the temperature of the water since it’s coming from a kettle. Through all of these improvements, we’re able to provide our own take on siphon brewed coffee and go a bit further to experiment with many other types of liquids, temperatures, ingredients, filtration levels, and vacuum pressures.
Here’s our recipe we’ve been using as a baseline. We’ve found that this works great for Ethiopian Natural and Kenyan coffees:
#12 Grind on the Mahlkonig EK-43 Grinder
Filter with 2 unbleached paper filters
Heat 425g+ water to ~202F in kettle
75g (3x) bloom for 5 sec, gently and quickly stir grounds
350g pour at 15 sec, pour down the side of top piece
Break crust at top of siphon
Draw down at 45 sec at 20% vacuum setting
Stir at just below half way, stir again just before drawdown finishes
Decant coffee and serve
Total drawdown should take less than 1:30
Result should be ~1.1% TDS and ~20% extraction
We hope that you’ll come by the store to take a look at the siphonbot in action and give us your feedback! We’ve had many people ask about how they can get one, so over the next couple months we’ll be working on refining the software and figuring out how to manufacture more than just the few prototypes we’ve built so far. The hope is to open up pre-orders in early 2019 for a small size run of early access customers to try these out and hopefully a larger run toward the middle of 2019.