Caffeine extraction

When we used to live in Broad Ripple I would buy coffee beans from Hubbard & Cravens’ roasting plant on 52nd Street next to the Monon once in a while. Their roast was a little too dark for my preference, and their hours were such that we started calling them Hubbard & Closed, so it wasn’t always at the top of my list of places to buy beans back then.

I was in the neighborhood, loosely speaking, earlier this week to pick up this month’s Bacon of the Month Club treat from Goose the Market, and I was low on coffee, so I stopped in the Carrollton location to pick up some beans.

Caffeine does not usually have much effect on me, but last night I was awake until 2:00. What happened?

When I got home I eagerly flipped on Miss Silvia, the espresso machine, in anticipation of a rich, invigorating beverage. I was immediately distracted by the dog’s silliness and other chores that needed attention. Some time later, I got around to making the shot of espresso that I had been looking forward to. It was good, so maybe I am coming around on my opinion of Hubbard & Cravens’ roast level.

Fast forward to this morning when I was laying in bed, unable to sleep. I had plenty of time to think about the cause of my insomnia.

Silvia’s boiler temperature is controlled by two simple bimetallic thermostats, so temperature regulation is not very precise. Temperature swings of 40° are not unheard of with this type of thermostat. When I brewed my espresso yesterday evening, I noticed that it was extremely hot. The thermostat must have just cycled off at the very top of its 110°C (230°F) range. (I am certain that I had not left the steam switch on, which brings the boiler to 140°C [284°F].) The espresso even appeared to be boiling as it came out of the portafilter.

Wikipedia says that caffeine’s solubility in water increases dramatically with temperature.

Not being a chemist, I have to assume that caffeine’s solubility would continue to increase with temperature. So, it is definitely plausible that if the water was much hotter than normal for that fateful shot, the machine could have extracted much more caffeine than normal into my espresso.

If the solution to this is better temperature control, am I trying to talk myself into joining the ranks of people who have hacked their espresso machines to include a PID controller? Uh-oh.

2 Responses to “Caffeine extraction”

  1. Michael Mays says:

    The amount of caffeine in the amount of coffee is much less then the solubility of caffeine at room temperature. So temperature was not the culprit of your long ago insomnia.

    Also the darker the roast the less caffeine in the resultant bean. Caffeine sublimates. Higher roasting temperatures and longer times allow more of the caffeine in the green bean to dissipate in the roast.

  2. Christopher says:

    But if the water is at a higher than normal temperature as it passes through the grounds, it can pick up more caffeine, right?

    In other espresso machine related news, I finally convinced myself this week that the 110°C thermostat was stuck closed, resulting in only the 140°C steam thermostat controlling the boiler’s temperature. $16 for a new thermostat shipped to the house, and we should be back in business tomorrow.

    I’d suspected this had been happening occasionally, and this weekend, it seemed like it was always too hot. I measured the temperature of the water as it came out of the machine, and it was not over 110°C. Then it dawned on me that, of course, the liquid water can’t be over 100°C unless it’s under pressure. Measuring the boiler temperature directly on the surface was the final hint I needed. Maybe more hint than most people would have needed, but I finally got it!

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