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It's gospel among serious bakers that measuring by weight is far more accurate than measuring by volume. However, I'm not sure that measuring by weight helps at all when you have varying humidity levels. It seems to me that, if the recipe author has much higher or lower level of humidity in their kitchen than you do, measuring by weight would tend to make differences in water balance even worse.

For example, I recently made the same pizza dough recipe in my apartment (65F, 80% humidity) and at my in-laws (75F, 35% humidity). Getting the same texture of dough was a difference of 2/3 of a cup of water, or around 6oz of weight. This water already was clearly in the flour in my apartment, adding to its weight but adding somewhat less to its volume. This means that if a recipe was written by someone in Tuscon and I made it in San Francisco, I'd get a sticky mess of a dough without enough flour.

Unfortunately, I'm not in a position to make repeated experiments in measurement at different humidity levels to see if weight or volume is more accurate when the hydrometer is going up and down. Is anyone?

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This is quite extreme. 35% and 80% are about the limits at which the average human still feels comfortable (and even needs slight acclimatization). Most people in a temperate climate live at between 45% and 55% humidity, and within that range, the variation in flour should be minimal. –  rumtscho Oct 11 '11 at 9:42
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@rumtscho, you must not live in the US! This kind of variation is not abnormal –  Ray Oct 11 '11 at 14:08
    
If your ingredients were getting damp in high humidity, they would go bad and you'd throw them out. Keeping your food correctly in correct containers/fridge/larder will minimise any fluctuations in atmospheric humidity. –  Rincewind42 Oct 14 '11 at 3:55
    
Everyone: thanks for the responses. I appreciate the thought an passion which went into them. I was really hoping for some empirical, experimental data though rather than what people feel is correct. I think baking by weight is probably more accurate too ... but I don't know. Especially after the pizza dough incident. As such, I don't really feel that this question was answered. –  FuzzyChef Oct 25 '11 at 3:06
    
@Ray I know that there is such a variation throughout the continent, I just mean that there aren't that many people who bake in Arizona one day and Florida the next. –  rumtscho Nov 14 '11 at 20:32
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3 Answers

up vote 6 down vote accepted

Changes in the weight of ingredients due to humidity are very small compared to changes due to how loose or tight your flour gets packed into the measuring cup.

Weighing the ingredients eliminates one (major) source of measurement error. You'll still have to compensate for other things on your own.

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And as rfusca points out, it's easier to compensate for differences in humidity, especially if you have some way to measure it. If you scoop, you have no idea how packed the ingredients are. –  Nathan Oct 11 '11 at 13:16
    
This comes closest to an answer to the question I asked. Guess I'll have to be satisfied with that. Thanks. –  FuzzyChef Oct 25 '11 at 3:07
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I had the same question and found some old-ish scientific material

According to this, at 21°C, 45 % relative humidity can reduce flour weight by 22 %, 75 % relative humidity can increase flour weight by 15 % from an assumed "normal" 60 % at the same temperature. These values may vary with other base temperature and relative humidity.

Most ingredients are not as prone to density-changes as flour is. Flour can be compacted massively and significantly fluctuates in density, independent of it's moisture content. (see using volume measures to estimate mass to get an idea about the weight range at the same moisture content in the same cup)

So I guess, if your humidity and way of packing into the cup or other volumetric measuring container (e.g. fluff the flour up through sifting, then pack it tightly and level every time to provide reproducible fluffiness) does not change much, you can go with a volumetric measurement for flour just as well as with weight.

With most other things like sugar, butter etc, don't seem to change density and thus can be measured in volume as well as weight, providing you always "level" the ingredient to have reproducible amounts. If you don't level, it's a matter of chance to get the same heap on the top. This is only true for those ingredients you can relatively tightly pack.

I guess, if you want to be super-accurate with flour, you need to calculate the density (which you can do at home) of your flour and then determine the moisture content (which is rather difficult I guess - you could try drying your flour for a couple of hours and then weighing and measuring the volume, but be careful preparing it the same way for the volume every time!).

All up, with flour most good recipes state add more flour or liquid if necessary and I guess that has it's reason...

This may also be related to different qualities of flour which can take up more liquid - or not. It's just a bit annoying if you don't have experience with the necessary texture :)

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Is it more accurate? ABSOLUTELY

Does it mean that you can still follow a recipe by weight exactly and expect perfect results everytime? No

You're right in that humidity will vary the weight, but if you're consistently working in the same area with a small change in humidity - its not something to worry about. You'll adjust your recipe once and then generally stay in the same range. Going by volume, you're always going to be all over the board. Sometimes you'll pack light, sometimes tight. Going by weight, you're going to be pretty close as long as none of the variables have changed drastically.

The problem you run into is when you change locations or the humidity changes drastically. In the long run, you'll need to know what your expected dough should look and feel like. After you've baked a loaf 100 times, you'll poke it and know if its too dry.

In addition to the feel of the dough, I have a hygrometer in my kitchen. Keeping an eye on it lets me know if I should expect to need to add more or less water to my dough. I bake A LOT, so I keep an eye on this to make life easier.

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As an aside, in Europe all baking is done by weight. Tablespoons and teaspoons are still used for smaller amounts, for things like vanilla essence, for example. –  ElendilTheTall Oct 11 '11 at 7:39
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Sending this one to my mom so she can maybe finally make the shift to baking by weight and stop cursing the gods for ruining her cookies and cakes. She's in New England though, a notorious humid and changeable land. –  Katey HW Oct 11 '11 at 13:46
    
@ElendilTheTall - yup, I know and I'm jealous of that fact. I've a few recipe books with good recipes buy they're volume and they annoy the crap outta me. I've taken to just weighing them out and writing in the weights in the book. –  rfusca Oct 11 '11 at 14:54
    
I have a particular hatred for books/websites that use cups and tablespoons as a measure. Pray tell how you measure half a cup of butter without making a mess. By weight is easier much of the time. Additionally, just what is one cup. To copy a recipe we all have to be using the same cup. However, we are not: en.wikipedia.org/wiki/Cup_(unit) –  Rincewind42 Oct 14 '11 at 3:57
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