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Thread: new milk thermometer question.

  1. #1
    Senior Member Rocky's Avatar
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    new milk thermometer question.

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Just bought a new thermometer. I have just noticed that it reads 30 C .
    I was expecting it to read 0 C.
    My Son said 30 C would be correct as you would not expect it to read 0 C when the ambient temperature is about 30 C.
    My old thermometer used to read 0 C until you put it in the cold milk when the temp would drop and then the temp would gradually climb as the milk was heated.
    On the old one you could twist the top of the thermometer to 'zero' it before steaming.
    Is the new one 'broke' or should it read 30 C straight out of the box.




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    It should read ambient temperature.
    That said, analog thermometers are quite unreliable. They often need to be calibrated as described above. Well worth spending a little extra for a digital thermometer, which is much more reliable.

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    Senior Member LeroyC's Avatar
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    It should read roughly whatever the temperature is in your house at the time. It wont be super accurate as its designed to be immersed in something, but it should still be within about 5deg of the actual temp. So unless its actually 0deg in your house it definitely shouldnt read 0.

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    Senior Member Rocky's Avatar
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    Thanks Guys. So when I put it into the jug of cold milk, the temp on the dial should drop to the temp of the milk and then steadily climb when I start steaming.
    (The reason I'm confused is because my previous thermometer always read 0 C before I put it into the milk.)

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    Senior Member level3ninja's Avatar
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    Quote Originally Posted by Rocky View Post
    Thanks Guys. So when I put it into the jug of cold milk, the temp on the dial should drop to the temp of the milk and then steadily climb when I start steaming.
    (The reason I'm confused is because my previous thermometer always read 0 C before I put it into the milk.)
    Yes that's correct. Mine usually reads a few degrees higher than the ambient air temp

    If it has a hexagonal nut on the shaft directly under the dial case it can probably be calibrated. Best way to do this is to fill a cup with ice and then top up with water and insert the thermometer. While still in the water hold the hex nut with a shifter or similar and turn the dial case until it reads 0C. Be careful to make small gentle adjustments as I snapped my last one calibrating it for the second time after moving house (maybe something happened first during the move, who knows). You probably know how to calibrate it but just in case anyone else is reading this in future wondering.
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    Senior Member Rocky's Avatar
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    Thanks Ninja, I just find it amusing (and a little annoying) that I was so ignorant about the thermometer.
    I have only had the one since I bought my Espresso machine in about 2008 and I just took it for granted that the thermometer read zero when not in use.
    When I looked at the new one today I was stunned to see it read 30 C - thought it must have been faulty!
    Even my Son who has never used one knew that it should show ambient air temp 'at rest'.

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    Senior Member level3ninja's Avatar
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    I'm quite curious about your thermometer, it must have a temperature threshold at which it drops to zero? When did it start showing a value? You said above when you put it in the milk it would drop then rise, so it went negative when it was in cold milk? Could it just be that you had calibrated it with zero as room temp?

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    You should check / calibrate it Rocky.
    Notice the hex head nut on the underside.
    Hold with a shifter gently rotate dial.
    Rest the thermometer in an iceblock and calibrate a 0 deg.
    Use solid ice.
    I use a bottle that I've put a sealed plastic tube into first
    And fill n freeze.

    Check it from time to time.
    Vast majority of cafes don't check / calibrate
    at all.
    Which explains why you get temps all over the place.
    GL

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    Senior Member Lyrebird's Avatar
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    Quote Originally Posted by EspressoAdventurer View Post
    Rest the thermometer in an iceblock and calibrate a 0 deg.
    Use solid ice.
    Do not use solid ice.

    Use a mix of ice and chilled water, this is an example of a frigorific mixture and will sit at a stable 0 oC until the ice melts. 50 / 50 works well.

    Solid ice will start at the temperature of your freezer (generally -18 to -20 oC) and warm towards 0 oC so you will not know the temperature.
    Last edited by Lyrebird; 19th January 2019 at 09:16 PM.

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    Senior Member Lyrebird's Avatar
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    As an aside that is probably of interest only to those who share my fascination with the history of metrology (the science of measuring things), the reason your freezer runs at about -18 oC is also because of a frigorific mixture but a different one.

    The standard freezer temperature is 0 oF, and Herr Professor Doctor Fahrenheit set the zero of his scale at the lowest temperature he could reliably obtain which was that given by a frigorific mixture of equal parts water, ice and ammonium chloride.

    Each scale degree is related to the linear expansion of mercury, hence the odd numbers in the scale (water freezing at 32 oF and boiling at 212 oF).

    So now you know.
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  11. #11
    Senior Member Rocky's Avatar
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    Quote Originally Posted by level3ninja View Post
    I'm quite curious about your thermometer, it must have a temperature threshold at which it drops to zero? When did it start showing a value? You said above when you put it in the milk it would drop then rise, so it went negative when it was in cold milk? Could it just be that you had calibrated it with zero as room temp?
    Yep that's it. With the old one I just twisted the head until it was at 0 C at room temp and then when I poured the cold milk into the jug it would go negative until I started steaming. You know when the milk is right regardless of the temp reading but it always used to read 70 C when the milk was ready, so I thought that was obviously the way to do it. I am gobsmacked to find out there is a lot more to it - ie - "calibrating the thermometer".
    I don't suppose I really need a thermometer anyhow (I know when the milk is ready) but I am used to having it stuck in the jug.
    I will do the calibration thing anyhow because I am a bit OCD and it appeals to me to "do it right".

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    Senior Member deegee's Avatar
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    As bosco said above these thermometers are not all that accurate. They usually read from 0 to 100 C and are seldom accurate over the full range. If you calibrate them at one end of the scale, they will usually be incorrect at the other.
    So I calibrate mine where I want them to be correct i.e. at 65-70C. Then I put a drop of superglue or run some araldite around where the nut meets the case, because I have found that it is too easy to accidentally "de-calibrate" them when cleaning or shifting them around the edge of the jug.
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    Senior Member artman's Avatar
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    Quote Originally Posted by Rocky View Post
    .... it was at 0 C at room temp and then when I poured the cold milk into the jug it would go negative until I started steaming. You know when the milk is right regardless of the temp reading but it always used to read 70 C when the milk was ready...
    This would mean you were steaming your milk to around 90deg , assuming your room ambient temp was 20. Ie your thermometer was reading 20 deg under actual.

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    or that its zero point had been set to a real -20

  15. #15
    Senior Member Rocky's Avatar
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    Artman - could you steam the milk to 90 C without burning it?
    During the few days I was without a thermometer, I was just using my own judgement. Steaming until the milk expanded to the top of the jug and I was satisfied with the quality of microfoam. Milk seemed to be about the right temp when poured into the cup - just a little too hot to drink.
    Of course you can't go by the microfoam as the fat content of the milk varies wildly and sometimes it steams beautifully and sometimes not.
    Made me wonder if everyone on here uses a thermometer or just wings it.

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    I use a thermometer which I have previously checked against a professional temperature thermocouple device. It is near enough to do, but cheap thermocouples also have slow response times so you need to shut off before it reaches the desired temperature. After 5-10 seconds the thermometer will catch up. The less milk you are steaming, the earlier you have to shut off. If doing a single piccolo (60 mL of milk) I shut off at 50 and still it races over 60. For 180 mL for a normal cap+latte for two of us, 60 will stop it by 65, which I think the ideal band.

    My suggestion to you, Rocky, after calibrating your thermometer is that you shut off steaming no later than 65, preferably earlier, then watch the overshoot. Running to 70C will result in scalded milk.

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    Quote Originally Posted by Rocky View Post
    Artman - could you steam the milk to 90 C without burning it?
    During the few days I was without a thermometer, I was just using my own judgement. Steaming until the milk expanded to the top of the jug and I was satisfied with the quality of microfoam. Milk seemed to be about the right temp when poured into the cup - just a little too hot to drink.
    Of course you can't go by the microfoam as the fat content of the milk varies wildly and sometimes it steams beautifully and sometimes not.
    Made me wonder if everyone on here uses a thermometer or just wings it.
    G'day Rocky

    I used a so called "instant digital medical thermometer" to calibrate my manual ones. The medical one had around a 2 second lag - the manual ones are more like 10 seconds. You need to allow for the lag to get useful readings - however consistency is far more critical than the actual numbers.

    Normal full cream milk scalds at around 72 Celsius, so no, you could not get it to 90 without it breaking down (badly - curds anyone?). When you make microfoam you are slowly breaking down the lipids which creates some sugars and a few other stray chemical changes (overly simplified, but correct enough for froth). The sweet spot for both foam and extra sweetness is about 2 degrees before scalding, however the foam is OK about 15 degrees less. I found I could do a reasonable job by eye in terms of texture, however I could not nail the "extra sweet spot" reliably enough.

    Yep - I always use a thermometer as human skin starts to burn at 65 degrees and I prefer for a device to "take the heat" instead of my skin. Oh, and I really hate scalded milk.

    TampIt

  18. #18
    Senior Member Rocky's Avatar
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    OK, all done. That was an interesting experiment.
    As suggested by others, there was some variation (from my digital food thermometer) at the top and bottom ends of the scale. (about 5 - 10 degrees C)
    I have calibrated the milk thermometer to be most accurate towards the top of the scale.
    Thanks to those who took the time to offer assistance. I have learned something.

  19. #19
    Senior Member Rocky's Avatar
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    Well, I have now done two batches of milk using the new Thermometer and they have both been perfect.
    Hard to say why the thermometer would make that much difference.
    Maybe it is just a better creamier batch of milk, but the difference is massive. Technique has not changed at all.

  20. #20
    Senior Member level3ninja's Avatar
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    As TampIt mention above if you don't hit the right temperature to convert the lipids to sugars you won't have the lovely sweetness that steamed milk can have. Try steaming it 5-10C cooler and taste the difference (or taste it at about 60C then keep steaming to 70C and taste again).

  21. #21
    Senior Member Rocky's Avatar
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    The quality of the microfoam was 100% better than previous. Ridiculous level of improvement. Almost too much to be just technique.
    I'd like to think it is just the better temperature control with the new thermometer because it is currently as good as it gets.



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