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So I have just made my girlfriend a cup of coffee, for the first time using her method. Ignore how correct the method is, but I figure it is important to mention:

Step 1: 37g* of coffee beans are ground (by hand if that matters)

Step 2: This is placed on some kitchen scales in the {whatever a coffee filtering thingy is called} and 550g* of boiling water is added

I was amazingly accurate and poured exactly 550g* of water, then as I watched it filter through the coffee I saw the weight increase slowly, 1g* at a time until it ended up on 557g*.

This increase took a few minutes, and my girlfriend says it must be the scales. I tested by adding an item to the scales and watching them, and they didn't change, so I think it must be something to do with the coffee and the water, likely temperature.

My confusion is that due to evaporation I would actually expect the weight to go down if anything (realistically I didn't think it would be a noticeable difference, but still the only change I can think of).

Can anyone explain this gradual increase?

*this is just a standard set of kitchen scales, so not scientifically exact.

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    $\begingroup$ I'm voting to close this question as off-topic because it's (interesting) kitchen chemistry. $\endgroup$
    – Bill N
    Commented Feb 5, 2020 at 14:01
  • $\begingroup$ What you need to do is repeat the experiment for different parameters. Temperature, sugar instead of coffee and so on. And see what happens. $\endgroup$
    – Superfast Jellyfish
    Commented Feb 5, 2020 at 14:06
  • $\begingroup$ Not the main issue here, but mass of ground coffee is not necessary the same as the mass of coffee beans it was made from. For example, some ground coffee may remain in grounding device, etc. But probably for practical reasons you can approximate to the same mass. $\endgroup$
    – Agnius Vasiliauskas
    Commented Feb 5, 2020 at 14:30
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    $\begingroup$ What if you repeat the experiment as it is — does the result reproduce? What if you try the same without coffee? I suppose your scales have just drifted by 7 grams during the time of filtering. Try pouring the liquid out of its container and return the container back onto the scales. Do you get 0g reading? $\endgroup$
    – Ruslan
    Commented Feb 5, 2020 at 15:26

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It would be very easy to check if the scale changes because of temperature. Just use cold water instead of hot water when making coffee once.

From my guess, the hot water warms the scale and it sensors(Digital) or mechanical parts(Analog). A sensor is normaly calibrated for a specific temperature, so an increase in temperature of the scale and the sensor should result in a slowly changing reading.

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  • $\begingroup$ Looks like the warming scales theory is correct, cold water doesn't have the same effect, warm water always has the same effect. Thank you! $\endgroup$
    – SeriousBri
    Commented Feb 6, 2020 at 20:14

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