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Weight vs. Volume

Any scientist worth her salt will tell you that the two most important factors in any experiment are consistency and reproducibility. Considering that every time we bake we are essentially conducting a science experiment, why wouldn’t we hold the same standards in the kitchen?

When you write a recipe, it should be able to be followed by anyone in the world, and they should have the same results as you do in your home. Volumetric measurements (cups, tablespoons) are flawed. Weight (grams, ounces) is a consistent measurement. Don't believe me? Think using a scale is snobby? I present to you my case in three parts. I will disprove volumetric measuring by examine the tools themselves, the ingredients we measure, and the relationship between tool and ingredient. Court is in session.  

First, the tools:
We seem to believe that a cup is a cup, that it is a standardized unit, much like a mile or a watt. But it is not. A cup is quantified differently all around the world. Take, for instance, Australia and New Zealand: for them a cup is defined as containing 250 milliliters. In the US, when it comes to nutrition labeling, a cup is defined as containing 240 milliliters. In the UK a cup holds 284 milliliters, and in Japan it is a measurement of a mere 200 milliliters. So you see the inherent challenge with the tool itself, a cup is simply not a cup.

Even if you are consistent in your use of tool by nationality, your recipe yield stands to be quite different than what is stated in the cookbook. And what if you don't know what kind of cup you have on hand? Or what cup the cookbook author used in development? A cup may change, but 150 grams is always 150 grams. Members of the jury, I present to you our first strike against volume. Tools are flawed, weight is empirical. 

Now let’s look at the ingredient:
Do you think flour changes from day to day or is it a constant? Flour is, in essence, a pile if tiny grain particles. And those tiny grain particles are surrounded by even tinier pockets of air. While your flour might not be changing on a molecular level, we all know that air changes frequently. We experience this daily as the difference between a humid air and a dry air. When the air is humid, it is denser, more compact. Consequently when you measure flour on a humid day, you are actually filling that cup with more flour than you would on a dry day. The air in between the particles of grain is more compact, affecting the ingredient in a significant way. Members of the jury, I present to you the second case against volume. Ingredients (particularly dry ingredients) are not reliably voluminous ,but their weight does not change. The ingredient is flawed, weight wins again. 

Time to examine the relationship between tool and ingredient:
My final strike against volume measurements comes in how we handle the measuring cup. Do you scoop flour out and then level it with a knife? Do you pour flour into the cup and then tap it down? Try this at home and weigh the difference. When you scoop flour into a cup you are compressing the air in between the grain particles. Consequently you end up with more flour in the cup than you would if you took a spoon and filled the cup little by little. Again, we see the inconsistency in the cup. The amount of ingredient depends on method of filling. The relationship between tool and ingredient is flawed, weight wins!

I prefer a digital scale, but if this is what you have on hand USE IT.

But, of course, we must not forget the ease a scale brings to the kitchen. When we measure ingredients by scale, we only need to place a bowl on top, then fill and tare, fill and tare. No more measuring cups, tablespoons, etc. to wash. This time you only have one bowl to clean at the end of your baking endeavor. However, when we use extremely light ingredients (or values of small quantity) then we might be below the registered threshold on the scale. In that case it is appropriate to still use measuring spoons. This is particularly the case for baking powder, baking soda, and salt.

How do we know our scale is accurate? Water! Water has a uniform density of 1 gram per milliliter, which means one mL of water will weigh exactly one gram. Measure a few mLs of water into a cup on the scale and see if it matches the number in grams. If not, you must recalibrate your scale (or buy a new one). 

You might wonder what to do with the cookbooks on your shelf filled with recipes described with volumetric measurements. Do not cast them aside! And don't bother trying to convert cups to grams. If those cookbooks have been working for you this long, then by all means let them live in your collection. But moving forward won't you attempt a bit of accuracy in the kitchen? Buy a scale. Search out cookbooks described in weight measurements. I guarantee that after a few tries you'll be converted to the evangelism of the scale. Three cheers for accuracy, consistency, and reproducibility!