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Thread: Thermometer suggestions

  1. #1
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    Thermometer suggestions

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    I was thinking about getting a digital thermocouple thermometer for temprature surfing, and for milk frothing.

    Will this type of thermometer do both? And can anyone suggest where I would get a good cheap one?

  2. #2
    Senior Member fatboy_1999's Avatar
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    Re: Thermometer suggestions

    Andy,

    I dont know much about temp surfing, but for milk frothing, there is a standard type of thermometer that has a clip to attach to the side of a SS jug with a dial indicator. Ive seen them in 2 sizes.
    I have 2 of the small ones. I think the larger ones are more geared towards cafe use.
    I got mine at a Housewares shops for $10 each. Ive seen them priced up to $30 in some cases.

  3. #3
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    Re: Thermometer suggestions

    Andy,

    Ive generally found *that it is difficult to get an accurate idea of *the temperature of the brewing water coming out of the group shower (as in for temperature surfing) because the end of the thermometer is not immersed properly in the water that it is trying to check. Many of the more budget priced thermometers have quite a long "shank" that basically needs to be immersed almost fully for the temperature reading to be accurate. Therefore, I would think that in order to get an accurate measurement, you would need to find a thermometer that has a very small sensor on the end that will read immediately (so needs to be quick acting digital thermometer rather than analogue with a needle that needs to climb) it is bathed in brew water.

    Additionally you would use a vessel such as a foam cup to catch the water so that no temperature is lost to the material it (the vessel) is made of.

    Also, it is debatable whether any such reading will be "practically" accurate because the temperature of the water will change over the course of the pour...it cannot remain constant, because the boiler of a domestic machine has very small capacity, and there is no large mass in the group to stop heat loss as the brew water passes through the group from the boiler...and, the way that most domestic machines operate is that the hot water is pushed through the group, by virtue of displacement, as cold water is pumped into the boiler. IE the temperature of the brewing water, by virtue of the way in which the machine operates, will actually fluctuate and cool, resulting in the thermostat switching the element back on, after which the temperature of the brew water ( if still pouring), will rise again.

    You are therefore dealing with a kind of a sine curve effect in the way the brew water temp is "controlled" (if you can call it that!).

    So....practically speaking, the machine will deliver whatever it delivers, according to the way it has been designed and built, and it will either work ok, or it wont! You can judge that from the way the coffee is produced (if you have properly controlled the several parameters that the operator or "home barista" is reponsible for) without using any kind of thermometer to check the temp of the brew water.

    The simplest method of temperature surfing (to make sure that the brew water is "just right") is to wait until the thermostatic light goes out...therefore the electric element has just switched off...and at that point start water flowing from the group and you just see how hot and steamy it is. If you think it is way too steamy (and therefore too hot), let it flow a few seconds, the flow will settle down...stop, apply the group handle, and brew your coffee.

    Apologies if all this goes a outside the immediate scope of your question...

    In terms of a milk thermometer, an inexpensive dial thermometer will do, as mentioned by Fatboy.

    Regardez,
    FC.

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    Re: Thermometer suggestions

    Again, much appreciated FC for such a good reply. I know youre probably thinking about my other posting about the "low end" machine - so that helps.

    I went to check out the kitchen places, and ended up getting a really nice little digital stick thermometer from a place close to the Vic Markets. Its was $30, and had a 5 year guarantee! So I figure thats pretty good considering the other ones are $10-16. (small is 10, large is 16, and both have a "milk for coffee" range marked on them)

    Itll help me do a little surfing with the machine, as well as giving me an excellent reading when Im doing the milk because it has a little clip thingie too.

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    Re: Thermometer suggestions

    Ive been looking at thermometers of late. Mainly for roasting though. A couple of the kitchen supply places Ive been to sell a digital thermometer with a stainless steel probe on a one meter braided cable. They are designed for sticking into meat in ovens so you can monitor the internal temperature as the meat cooks. The usually have timers and target temperature alarms. The two Ive seen were $40 and $68 and had an upper limit of 200*C so no good for roasting. Kind of overkill for milk too.
    The thermocouples Ive found at Jaycar and DSE were both around the $100 mark. If you do a little research at sites like CoffeeGeek and alt.coffee you might find suggestions for temp surfing with thermocouples. Im sure Ive seen line graphs that profile the temperature at the group during a shot.

  6. #6
    Mal Dimal's Avatar
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    Re: Thermometer suggestions

    Hi All,

    For your info, Jaycar sell a small DMM that comes with a thermocouple (Bead Type) that is well suited for roasting, brew temp monitoring, etc. The best thing about it is, it is cheap ($24.95) but reasonable quality. Have a look via this link http://tinyurl.com/6bl6y

    Its a very handy little DMM, Ive used it for quite a few jobs already and not all of them related to coffee either (yeah I know, all times wasted whats not spent on coffee). Anyway, if you have a look at the specs, Im sure youll be impressed. All the best,

    Mal.

  7. #7
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    Re: Thermometer suggestions

    A clue about using the DMM. If you use this for raosting and you do this outside, keep the DMM out of the sun. Potential consequence 1 is the LCD displays goes black. It recovers but is useless in the meantime. Consequence 2 is the sun melts the glue attaching the face plate which in turn starts to detach itself and distort. I bought the QM 1445 which may not be from the same manufacturer as the one Mal has identified but better to be warned in advance.

    Cheers,

    Graeme

  8. #8
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    Re: Thermometer suggestions

    Heartily agree Graeme,

    Mal.

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    Re: Thermometer suggestions

    I went out and bought the DMM Mal mentioned.
    Will the bead thermocouple thingy take high temperatures? I know this sounds really silly because I think it is rated to 1000*C but I ran my heat gun briefly, just to check temp output, and the plastic bit near the end seemed to be melting a little?
    Do these thermocouples melt? More worried about the plastic and shoe lace looking bit.
    Also, I tried measuring the temp of the water as it exited the group head and the probe failed to measure anything above room temp? ie the thermocouple doesnt appear to able to measure the temperature of liquid?
    Anybody got any suggestions, tips, answers, ideas et al...?

  10. #10
    Mal Dimal's Avatar
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    Re: Thermometer suggestions

    Quote Originally Posted by sharkboy link=1107831413/0#8 date=1108124789
    I went out and bought the DMM Mal mentioned.
    Will the bead thermocouple thingy take high temperatures? I know this sounds really silly because I think it is rated to 1000*C but I ran my heat gun briefly, just to check temp output, and the plastic bit near the end seemed to be melting a little?
    Do these thermocouples melt? More worried about the plastic and shoe lace looking bit.
    Also, I tried measuring the temp of the water as it exited the group head and the probe failed to measure anything above room temp? ie the thermocouple doesnt appear to able to measure the temperature of liquid?
    Anybody got any suggestions, tips, answers, ideas et al...?
    Hi sharkboy,

    Taking each of your points in turn:

    * The "bead" of this t/c is the actual junction of the two materials, usually autogenously welded or silver soldered for medium temp applications (below the melting point of silver solder which is about 750 C IIRC).
    The substance you can see melting will be a piece of heatshrink tubing that they have used to "tidy" up the end of the fibre-glass insulation... nothing to worry about.

    * Im not sure what you mean by the "shoe-lace looking bit" but if you mean the white fibre-glass insulated wire between the t/c junction and the banana plugs, well this is still part of the t/c.
    The t/c comprises two dissimilar metals connected at one end (the junction) and the remaining two legs connected to an instrument that measures the very tiny voltage variations (in milli-volts or part of a milli-volt) that occur as the junction temperature varies.
    There are many different types of t/cs used in industry that utilise a range of differing materials in their construction and hence possess different performance characteristics from each other. Some types are more suited for particular applications over another. The type used by this multimeter is type K.

    * If you dont observe a reading on the DMM when you subject the t/c junction to significant increases in temperature, something is most definitely wrong. It could be one or more of the following:
    1) T/C not plugged into the DMM correctly - Check to make sure that you have the positive and negative plugs orientated correctly in the DMM. Red plug into the +ve socket (V Ohm mA) and the Black plug into the -ve socket (COM).
    2) DMM Function/Range Selector incorrectly selected - Make sure that the Temperature function is selected, identified with C (Centigrade) symbol. It might be necessary to "jiggle" the selector knob through a couple of positions either side of this just to make sure a good connection is being achieved. With such small voltages involved, a good connection is essential.
    3) The t/c is faulty - The t/c junction may be broken or a lead connection may be broken or a plug connection may be broken. This can be verified by plugging the t/c into your DMM, select the Resistance Measuring function on the 200 Ohm scale and note the reading on the display.
    You should get a reading of less than 50 Ohms on this scale and if it is anything significantly higher than this or "open circuited" then the t/c is faulty.
    It might be possible to repair the t/c rather than send it back if you are a dab hand at silver soldering. If you arent interested in doing this yourself, you can notify Jaycar of the problem and they should be able to furnish you with a working replacement.
    4) The Temperature Function of the DMM may be faulty - If as a result of testing the t/c as outlined in 3) above the t/c checks out to be OK, then it is possible that the DMM is faulty and needs replacing under warranty. Jaycar are pretty good about this sort of thing and Im sure theyll replace it for you without hassle.

    * T/Cs are used to measure all manner of substances including solids, liquids and gasses and even plasma. Provided the t/c is OK, it may be that the t/c junction isnt coming into contact with the Brew Water from the shower-head.
    Another way to check whether its working or not, is to try it out with your heat-gun again (ignore the melting plastic, its going to melt off during roasts anyway). You should observe a rapid rise in the displayed temperature on your DMM while the t/c junction is in the path of the heated air. If not, the t/c is probably faulty (see above).

    Hope the info above proves useful to you and that you can get it working. All the best,

    Mal.


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    Re: Thermometer suggestions

    Thanks for the detailed reply Mal.
    I used the probe whilst roasting this afternoon and it seemed to work well. I have an infrared thermometer aswell but it seems to measure about 10*C higher than the bead immersed in the bean mass.

    I tried measuring water temperature again (about 30 seconds ago) and still no result. I literally dipped the bead thermocouple into a glass of hot water and it didnt move off the ambient air temp even though the water in the glass was approx 55*C. I measured the water temp with my milk thermometer ;)
    Im still a bit baffled by the inability to measure liquid temps...?

  12. #12
    Mal Dimal's Avatar
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    Re: Thermometer suggestions

    Behmor Brazen - $249 - Free Freight
    Hi again SB,

    Sounds like the Auto-Compensation component of your DMM might be at fault. Id suggest that you contact Jaycar and ask them to replace your meter and t/c.

    My DMM for example has no difficulty measuring liquid, gas or contact temperatures from ambient up to 250 C with a one degree incremental gradient all the way through. Yours should do the same so Id say replace it. All the best,

    Mal.



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