Posted Mon Jun 25, 2012, 8:04am Subject: Re: Water thermometer?
We have a Thermapen and love it. Fast and accurate. Never would have bought it (gift from my Mother-in-law).
I've also got a much cheaper OXO thermometer that's holding up well; I enlarged one of the outlet holes in the lid of my Hario Buono and just sit that thermometer in that hole while the water is heating. I only turn it on after the water is mostly heated (I've gotten really good at predicting 195ºF by sound) and this eliminates read-time lag. The lead is already hot, and it keeps up pretty well as the water continues to rise up to 200-207ºF (which I then use to rinse or pre-heat the vessels I'll use for brewing, and it cools down to brew temp). I think I paid $20 for it at BB&B, and you can certainly get by like this.
I have a friend who brews tea and can get within 5ºF by sight... puts me to shame.
It's expensive, yes, but it is ridiculously fast and accurate. It uses an actual thermocouple rather than a thermistor which is why it's more expensive, but also why it works so much better than the cheap ones.
That's a very nice looking probe. But thermocouples are not inherently more accurate or faster than thermistors. If anything thermistors tend to be more accurate and more stable over time. Thermocouples have a wider temperature range but that isn't important for coffee brewing. The main disadvantage with a thermistor is that its output is non-linear so the electronics have to be more complicated.
You can buy a tiny thermistor bead for $3 that is accurate to +/-1°C at brew water temperature and has a very fast response time. It can easily be made into a small, flexible, waterproof probe and still retain fast response. If you calibrate it the accuracy can be improved. For $10-15 you can buy one that is accurate to a fraction of a degree out of the package. All you need is an ohmmeter to read one. Admittedly, using a table to convert to the temperature would bug most people, but for cheapskates it's a viable option. And a small flexible probe can reach places that a rigid thermometer can't.
I bought one of these $15 Taylor 9847N probes at BB&B a number of months ago. It's a little slow to reach a stable reading but has otherwise seemed satisfactory for brewing coffee. Recently I purchased a second one to implant into my moka pot. I took the time to check the accuracy of these two as compared to a US Sensor KS103J2 precision thermistor, which is guaranteed to be accurate to ±0.1°C up to 80°C 70°C. Above that temperature US Sensor makes no claims.
The thermistor in the Taylor probe is a tiny glass encapsulated bead of unknown make. It has a resistance of 1 kohm at 25°C.
The two Taylor probes differed from one another somewhat consistently by a fraction of a degree. More interestingly they both read low compared to the precision thermistor up to about 60°C and read higher than it for higher temperatures (see graph). So it appears that I had been brewing about half a degree Celsius cooler than I had thought.
To prepare it for my moka pot I carefully removed the tiny thermistor from the metal tip of the second Taylor probe, and then protected the wires and thermistor with a thin coating of epoxy. This had a pronounced effect on the response time. The factory version takes ~25 seconds to go from room temperature to a stable reading when immersed in water above 90°C whereas the stripped down probe is stable in under 10 seconds. There's too much metal in the Taylor probe tip.
Posted Tue May 21, 2013, 8:52pm Subject: Re: Water thermometer?
I notice you used 0C to test both Taylor thermometers against your precision thermister. Was that in an ice-water bath?
It seems that the variations of each were within 0.9C which is probably OK for coffee (and other cooking).
I wonder if those thermisters have the same error up around 100C which is where you would be doing a lot of testing for coffee.
I tested mine in boiling water and found a source of error in the gradient between the bottom and top of the boiling pot (currents?) and wonder if my ice-water bath had a similar gradient between the top and bottom.
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 7,781 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
Espresso: ECM Vene. A1, La Cimbali M32 Grinder: Azkoyen Capriccio, Major Vac Pot: 40s era Silex Drip: Msl. Com. brewers Roaster: gave it a try, decided no
Posted Wed May 22, 2013, 5:42am Subject: Re: Water thermometer?
I use the Taylor NSF digital unit, it is inexpensive and works well for me in all my kitchen duties. Nothing against the Thermalpin, they are great but a bit more on the expensive side. Click Here (www.chefsresource.com)
In real life, my name is Wayne P. Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!
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