Sunday, September 6, 2009

Temperature Surfin' Safari: Latte, home

The Rancilio Silvia's thermostat light is a pretty good indicator of how hot things are. If the light's on, the thermostat knows it's not hot enough in there, and it's heating up. Logic would dictate that once the light goes off, we're ready for coffee, right?
It's not quite that simple, unfortunately.
The thermostat isn't quite smart enough to know when it's exactly the right temperature. It also doesn't realise that after you turn the heating element off, it will still heat things up a bit more for a few seconds. So if you turn on the pump as soon as the light turns off, you'll hear a hissing sound. That's the water turning into steam. It's too hot. Your beans have travelled thousands of kilometres to be in your machine, and the last thing they want before they finally land in your cup is an unexpected layover in Too Hot City.
Furthermore, that time in between "I've just finished heating up" and "I'm heating up" is separated by minutes of just one thing: the light is not on. The temperature can vary by up to 30 degrees. Not at all the predictable coffee environment with as few variables as possible that we would hope for.
Thankfully, there are hundreds of people on the internet who have been doing experiments towards getting around this temperature problem. One way is to install a PID controller: a microprocessor takes temperature readings and does a very good job of knowing when to turn the heater on and off. Another way, much cheaper and less machine-altering (though not nearly as effective), is through temperature surfing.
Temperature-surfing techniques for the Rancilio Silvia seem to fall into two categories:
  1. Wait a certain amount of time after the light turns off, catching the machine on its way down from the way-too-hot zone, or
  2. Wait a certain amount of time after the light turns on, catching the machine on its way back up from too-cold.
The first method is the one I've been using, mainly because it gives you a lot more time to play with: you've got two minutes after the light goes off. And I'm a bit of a novice with the whole dosing/tamping thing, so I could use that extra time.
Today was my first try with method #2: 45 seconds after the light goes on. That means I have to sort out my grinding first, but at least my tamping is a lot quicker these days.

Well, something unexpected just happened. While writing up this entry I started googling around, trying to find where I read about the two minutes or forty-five seconds thing. And it turns out I can't find it. I'm finding all sort of numbers. Thirty seconds after it goes out? Two seconds of water, then go for it? A whole gaggle of data, with no definite conclusions? I'm not really sure who to believe now. But I know two minutes is too long. I cut that to a minute and a half a while ago, which was a small step in the right direction, but I think it's going to take another giant leap to get some real results. Let's go with thirty. If nothing else, I'll save six minutes of standing around if I make four coffees in a row.

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