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Water Weight, WTH!!!!

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    Water Weight, WTH!!!!

    The short of the below is, there is a weight difference of liquid and fluid ounces.

    Being the man of science, clearing up myths and misinformation related to BBQ and cooking, this could be for Meathead. At best I consider myself a pretty mediocre cook/BBQer. That said, I also believe I’m a very well-informed mediocre cook/BBQer. I take in reading, watching, and listening to a lot of cooking information from a verity of sources including: AmazingRibs.com (the best), ATK, Alton Brown, Foodnetwork.com, Milkstreet.com, Thespruceeats.com and so on.

    I always knew part of why I was a mediocre cook was because I frequently just used what I had on hand, often significantly altering recipes, and eyeballing a lot of measurements. A while ago I decided to change my ways and to actually start measuring things. To keep things simple, I wanted to do that using a scale, so I came up with a simple conversion chart. There were several difficulties with that, like how much does 1 cup of diced green pepper weigh, what does a cup of all-purpose flour weight… One thing I knew for sure, so I thought, was regarding water “a pint is a pound the world around”. I was working off the assumption that 1 cup of water/watery liquid (vinegar, broth, skim milk) weighed 8 ounces/226.8g.

    Just recently I noticed somewhere listed a teaspoon of water weighed 4.93g. The math on that to get to a 8oz/226.8g cup just didn’t work. That bothered me so eventually I weighed a cup of water for myself. Of course, this is where I discovered a cup of water weighs well over 8oz/226.8g. My scale is only so precise, but it’s about 240g. WTH is going on and why am I only finding this out now! So many people/websites endorse the precision of using grams rather than volume (a concept I completely agree with), but never have I heard there is a difference between fluid ounces and dry ounces. What a stupid system! Now I know and somehow the rest of the world needs to be told. Or am I missing something?
    Last edited by Matt Bykowski; August 9, 2020, 11:30 AM.

    #2
    Measuring the volume of anything with cups and teaspoons is inaccurate because only a tiny difference in the height of the liquid in the container -- a change that might not be easy to see -- will make a distinct change in the weight.

    Another problem is measuring spoons and cups are not made to scientific precision - they can vary a little bit from manufacturer to manufacturer.

    These are two main reasons why measuring by weight is more consistent.

    The saying "a pint's a pound the world around" is ONLY accurate for water. Water has a density of about 1 ounce (weight) per 1 ounce (volume), which is why this old saying works. If you're talking about anything else, all bets are off.

    The reason why you're confused is you've made the unconscious assumption that the density of everything (the weight per volume) is the same as water. A lot of people do this. But think about it -- A pound of feathers is a LOT bigger than a pound of lead, right? That means the density of feathers is a lot smaller than the density of lead.

    "...a teaspoon of water weighed 4.93g, The math on that to get to a 8oz/226.8g cup just didn’t work...."

    These numbers are reasonably correct mathematically, except you aren't going to get that kind of accuracy if you measure the volumes with normal household teaspoons and measuring cups.

    You're blaming the math and the scale when you should be blaming the errors created by your (and everyone else's) inability to fill said spoons and cups to 0.1 gram accuracy. Even 1 gram accuracy will elude most of us.
    Last edited by IowaGirl; August 9, 2020, 07:05 AM.

    Comment


    • Matt Bykowski
      Matt Bykowski commented
      Editing a comment
      Thanks for the reply, I was pretty much referring to water. I wasn't doing things like assuming a cup of flour, rice molasses would weight 8oz. Overall should a cup of water weight exactly 8 ounces? My only point/question is using, what I think is, an accurate scale I get a weight of noticeably more than 8oz per cup.
      Last edited by Matt Bykowski; August 9, 2020, 10:59 AM.

    • IowaGirl
      IowaGirl commented
      Editing a comment
      The density of water varies with temperature. A precisely measured (almost frozen) 1 cup of water will weigh 1.043 pounds at 32F / 0C. At 70F / 21C, 1 cup of water will weigh 1.041 pounds. At 212F / 100C, an (almost boiling) 1 cup of water will weigh 1.036 pounds.

      But to see this minuscule difference, you can't use any ol' measuring cup dug outta your baking drawer. For everyday people with common measuring cups, yes, a pint (of water) is a pound the world around.
      Last edited by IowaGirl; August 9, 2020, 01:39 PM.

    • shify
      shify commented
      Editing a comment
      Matt Bykowski - you are missing the point, which is that you cannot accurately measure 8 fl oz of water in a measuring cup with any large degree of accuracy. Try to measure it out by volume 5 times and then weigh it and guarantee you will get five different weights. That doesn't mean 8 fluid ounces of water weighs differently every time you measure but that your 8 fluid ounce pour =/= exactly 8.00 fluid ounces. Do the same thing with a scoop of flour and you'll get the same result

    #3
    I should also add that measuring dry ingredients by volume is even more inaccurate than measuring liquids, because the density of the dry material can vary a lot depending on whether the material is packed down tight or aerated and fluffy. Flour is a grand example of this problem.

    Comment


    • grantgallagher
      grantgallagher commented
      Editing a comment
      Lol. I almost lost it on this post before i reread and realized u said by volume. Pound of feathers pound of lead.

    • IowaGirl
      IowaGirl commented
      Editing a comment
      I used to teach math and science to undergrad college students, many of whom were math-and-science phobic. It was interesting to learn how people see the world differently based on how familiar and comfortable they are with science. As an example, this discussion of density -- how much a given volume of different things weigh -- was an eye-opener for many of my less science-y students.

    • Matt Bykowski
      Matt Bykowski commented
      Editing a comment
      Right, which is why I was using weight.

    #4
    Welcome to the enlightenment.
    IowaGirl breaking down for us. Love that. Worth the price of the pit membership right there. 👏👏

    Comment


      #5
      Get yourself a copy of the Food Lab by KENJI from Serious Eats. I bet you will enjoy the.book, it’s an interesting education in cooking.

      Comment


      • RonB
        RonB commented
        Editing a comment
        And some pretty good recipes too...

      • Matt Bykowski
        Matt Bykowski commented
        Editing a comment
        Thanks for the recommendation, I'll have to check into it.

      #6
      My post probably wasn't written very well. I absolutely realized the "“a pint is a pound the world around” only referred to water, not feathers or lead.

      Comment


      • ScottyC13
        ScottyC13 commented
        Editing a comment
        The expression refers to a British pint, which is 20 ounces not 16 as in the US. Water weighs 8.33 lbs per US gallon at room temperature. So a pint is 1/4 of that or 2.08 lbs.

      • Matt Bykowski
        Matt Bykowski commented
        Editing a comment
        Interesting, one more wrinkle. Thanks. By the way, the gallon to pint weight would be 1/8th, not 1/4th.

      #7
      There are 236g in a cup. Not 226. So your confusion starts from there.

      Also, you talk about water and 'watery liquid') but adding anything to water will slightly change the weight per unit volume.

      This is one reason I a) started to use metric and b) weigh everything. It's just easier and more precise.

      Comment


      • RonB
        RonB commented
        Editing a comment
        236 g of water in a cup. Conversion from English to Metric 1 oz is 28.35 g, so 8 oz = 226 g.

        I actually wouldn't mind if someone explained the discrepancy...

      • rickgregory
        rickgregory commented
        Editing a comment
        OK, there are a couple of things going on here.

        First, there are 8 ounces in a cup. If OP was right and there are 4.93g in teaspoon then there are 236g of water in 1 cup. But you're right about the conversion factor... for weight. Oddly, there are 29.57ml to one fluid ounce of water. Volume, apparently, is slightly different from weight for water (I'd always thought that 1g = 1ml for water and it's very close... but not precisely equivalent).

        8 x 29.57 gives us the 236g.

      • Richard Chrz
        Richard Chrz commented
        Editing a comment
        These 3 comments in a row are why I love this site, and all scientific cooks. Because, as the theory of food relativity (a bit stolen, but, redesigned a bit.) When it comes to food, it is all relative

      #8
      RonB and RickGregory are more accurate with their 236 g water per cup. Your number contains rounding errors. Here's the math with better accuracy --

      At 70F / 21C, 1 pint of water weighs 1.041 pounds.

      Converting from pounds to grams --
      1.041 lb X 453.592 g/lb = 472.189 grams water per pint

      Convert from pints to fluid ounces --
      472.189 g water / 16 oz/pint = 29.512 g water per fluid oz

      Convert from pints to cups --
      472.189 g water / 2 cups/pint = 236.09 g water per cup

      That's enough mathy stuff for today ... even for me!

      Comment


        #9
        Originally posted by rickgregory View Post
        There are 236g in a cup. Not 226. So your confusion starts from there.
        Yes, that is my entire issue. I just assumed (I know, shouldn't do that), it would be 226 based on a cup being exactly 8oz, or so I thought. Now I've learned. Yep, I also realized the broth and other watery liquids would be slightly different. I'm sure mineral content in tap water also causes variations. I just didn't expect it to be as much as it was when I weighed the cup of water.

        Comment


        • rickgregory
          rickgregory commented
          Editing a comment
          See above math.

        • mnavarre
          mnavarre commented
          Editing a comment
          Temperature affects it too. 8 oz. by volume of 40F water will weigh more than 8 oz. by volume of 100F water. Luckily, unless you're baking, curing meat, or making sausage it just ain't gonna matter much. And kitchen measuring cups aren't exactly precision instruments anyway.

        #10
        Wow. My head is hurting. I need a drink. But I think it will be in a 12oz container, or approximately 340.2 grams. No, I didn't figure that out, went to one of those internet conversion sites so it is probably wrong lol.

        Or maybe I need a 40...

        Comment


        • Mr. Bones
          Mr. Bones commented
          Editing a comment
          Ahm'a slide right upside, an join ya, Brother!

        #11
        Originally posted by IowaGirl View Post

        Convert from pints to fluid ounces --
        472.189 g water / 16 oz/pint = 29.512 g water per fluid oz
        Now I know. I just expected it would be the 1 oz = 28.35g I've always been taught.

        I'm sorry for all the math on a Sunday, but I very much appreciate all your contributions/responses.

        Comment


        • IowaGirl
          IowaGirl commented
          Editing a comment
          1 oz by WEIGHT is indeed the same as 28.35 g, which is also a weight measurement.

          1 oz by VOLUME is not necessarily 1 oz by weight, however, and thus it is also not necessarily 28.35 g.

          As a rough estimate, it's okay to assume 1 fl oz ~= 1 oz (wt) = 28.35 g when talking about water or other very watery fluids such as tea, broth, etc. Even I do it, because that's close enough for most people and most situations most of the time.

          But y'all wanted the answers to 0.01 places, so there ya go.

        #12
        How Very Grand, an enlightenin, Much Appreciated!
        Brain. Hurts. Now.
        Must. Seek. Bourbon. LOL!

        Comment


        • IowaGirl
          IowaGirl commented
          Editing a comment
          I'm very much of a like mind, sir.

        • Mr. Bones
          Mr. Bones commented
          Editing a comment
          Cheers, Sister! IowaGirl

        #13
        Anyone else need a drink? Here's some more math:

        1 + 1= 2 (Imperial - not sure about Metric )...

        Comment


        • Mr. Bones
          Mr. Bones commented
          Editing a comment
          Heehee

        • Mr. Bones
          Mr. Bones commented
          Editing a comment
          I'm not quite full yet, perhaps we could dabble in some Whitworth conversions, as well???

        • Craigar
          Craigar commented
          Editing a comment
          Be very careful RonB 1 rabbit + 1 rabbit = many rabbits.

        #14
        Great insight and comments, thanks all.

        Comment


          #15
          Cooking posts that have math and science being talked about are the best. Lol

          Comment


          • Mr. Bones
            Mr. Bones commented
            Editing a comment
            Richard Chrz Oh, Lawdy, Lawdy, never even once claimed to unnerstand...

            But, that has never stopped me from enjoyin it, even fer a minute

          • Mr. Bones
            Mr. Bones commented
            Editing a comment
            My takeaway, which I already done knowed back in my triple-beam late '70's days, is:

            A 'Z' of Smokey Smoke should weigh in at~28.35~ish grams, minus mebbe a g fer a regular baggie, 1.5-3g+ fer a ziplock, dependin on construct...be it on my ol skool scales, or my MyWeigh KD-8000...

            OTOH... an oz. of my fave bourbons theoretically should weigh in at ~29.512~ grams, -ish, after, (natch), zeroin my scales fer th tare weight of my Beloved, an Omnipresent Kolder Mini-Measure
            Last edited by Mr. Bones; August 9, 2020, 09:04 PM.

          • Mr. Bones
            Mr. Bones commented
            Editing a comment
            Here's hopin I can take th Dunce Cap off, even overnight...

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