Winter Air Is Dry. Is It Ruining Your Baking? We Tested to Find Out

There's a common instruction in many baking recipes that goes something like this: Add water to the flour, then add more water, a tablespoon at a time, until the dough looks and feels right. Recipe writers and bakers often explain this as a necessary step to account for variations in air humidity—on humid days, you need less water for the dough, and on dry days, you need more.

I've long been suspicious of this. Over the years, I've edited enough recipes from some of the world's most knowledgeable bakers, people like Stella Parks, Andrew Jangigian, Tim Chin, and Nicola Lamb, and one thing that's fiarly consistent in their recipes is they call for exact dough hydration levels, measured to the gram, and don't ask you to tweak on the fly from there. They never suggest that ambient humidity needs to be managed when baking their recipes.

But being suspicious is one thing, knowing for certain is another. I wanted to find out: Is there any validity to the idea that moisture in the air can alter a dough to the point that it would require day-to-day adjustments to the basic formula? I decided to dive into the research and run my own test.

What the Research Shows

What I needed to learn was how much humidity flour can absorb, because that's what this is really about. A dough has two primary ingredients: flour and water. Sure, the water can be in the form of milk or some other liquid, and there can be other ingredients like sugar, salt, eggs, oils, and butter. But the bulk of a dough comes down to flour and water. If water needs to be adjusted due to ambient humidity, the flour is the apparent culprit, presumably carrying a hidden, shifting amount of water.

This is a question of interest to the food industry—commercial flour milling and baking on an industrial scale is a big-money business, so they would want to know how much risk flour humidity poses to them. They can't leave bread formulations to chance.

All the literature I've seen fully supports the idea that flour can act like a sponge, absorbing humidity from the air or releasing it into the air. This can be represented by a chart called a "moisture sorption isotherm," which maps a substance's capacity to hold moisture across a range of relative humidity levels at a given temperature. For wheat flour, a typical moisture sorption isotherm shows only a modest increase in stored moisture across low to moderate indoor humidity (up to around 50–60% RH), with moisture content rising much more sharply once humidity pushes into the very high range (around 75% RH and above).

My Real-World Flour Humidity Tests

OK, so we know flour can absorb moisture, but the research indicates it's to a relatively minor degree in normal conditions. I wanted to see for myself if that was true in practice, in my own home kitchen. To test this, I waited until the start of the cold season, when the air dries, radiators kick on, and some of us start getting chapped lips and bloody noses. It was the perfect moment. I took two identical mixing bowls and filled each with 128g (4 1/2 ounces) of all-purpose flour, which Serious Eats defines as 1 cup by volume. I put one bowl, uncovered, in my bedroom, where a hygrometer was reading around 30-40% humidity. I put the second 128g uncovered flour sample in a separate small room, set up a humidifier at full blast, and closed the door. A hygrometer in that room measured humidity at 50-60%.

These are good humidity ranges for the test, as they reproduce levels typical of many homes that have some degree of climate control over the course of a year. I left both samples in their respective environments and checked them a couple of times each day, recording the ambient humidity level and the mass of each flour sample.

Test Results and Observations

Each bowl of flour began at 128g. After 24 hours, both had lost mass. The flour in the humidified room had fallen to 126g, a roughly 2% loss. The flour in the dry room had lost 5g, roughly 4%. Over the following four days, the samples' mass remained stable.

Right away, this tells us a few critical things:

• The fact that the mass of my samples changed at all tells us that flour can indeed absorb and release ambient humidity.
• Both samples lost mass, so we know that my stored flour, which I keep in a plastic container with a gasketed lid, had the highest humidity. My best guess is that it was holding onto moisture from over the summer, when ambient humidity is often higher than what I could achieve in my humidified testing room. Because I keep the flour well-sealed, it remained relatively moist even a few months into the cold, dry weather season (this probably also tells you I don't bake very often at home, and my flour container tends to stay closed).
• Because both flour samples changed mass within the first 24 hours and then stabilized, we can conclude that in this fully exposed setup, the flour reached a new equilibrium within about a day. In a sealed container or large bag, that equilibration would be slower.

Now we need to do some math to find out if these changes in flour mass are enough to matter in a recipe. While my test didn't explore extreme humidity levels, it tested the high and low humidity ranges for most climate-controlled homes. At the same time, by leaving my samples fully exposed to the air with no protective packaging or container, I was allowing them to change as much as possible in those conditions. This means my tests should be pretty good at revealing whether ambient humidity is a legitimate concern for home bakers.

Just as a reminder, in my humid room, the flour dropped from 128g to 126g, a 2g loss; in my dry room, it dropped to 123g, so a 5g loss. Expressed as a percentage, that was a 1.6% loss for the more humid room and a 3.9% loss in my dry room.

Let's take a hypothetical 70% hydration bread dough: In baker's percentages, that means 70g of water for every 100g of flour. I don't actually know how much humidity my flour was holding at the start of the test, but let's just pretend, for argument's sake, that it's the "norm," and let's call it the "stored condition" flour. If I made a dough, then, using this 70% hydration formula, I'd weigh 100g of my stored-condition flour, mix it with 70g of water, and I'd have my 70% hydration dough.

Now let's assume I was making the same dough, but this time the flour is my humid-room testing sample that was 1.6% lighter in water weight than the stored-condition flour. We're going to pretend I'm a baker who doesn't actually know the flour's mass has changed due to water loss, so I still weigh out 100g of flour, except that now, there's 1.6g more dry material in my cup (because this flour lost 1.6g of moisture). So my humid-room flour is actually the dry-matter equivalent of 101.6g of my stored-condition flour. When I add 70g of water to that, it's not a 70% hydration dough anymore, it's a 68.8% hydration dough, which I think we can safely round up to 69%. So I lowered my dough hydration by about one percentage point without realizing it.

What about my dry-room flour? It lost 3.9% of its mass in the form of water, so that means when I measure 100g of it, it has the dry material equivalent of about 103.9g of my stored-condition flour. Combined with my 70g of water, I now have a 67.4% hydration dough, which is about a 2.5-point drop in hydration.

What's the Significance?

At the high end, I documented a ballpark 2.5% change in hydration, based on how much moisture flour seems to absorb or release across a typical range of indoor ambient humidity levels. The next question is: Is this enough to matter and justify recipes that take the less precise route while guiding readers to adjust on the fly?

As I mentioned before, I'm not a baker, so I didn't want to rely on my own judgment to answer this. Instead, I reached out to Serious Eats contributor and baking genius Andrew Janjigian for his take on whether these changes in hydration levels are meaningful or not. "In my testing, I find ±2.5% to be the threshold for noticeable texture differences, though it takes at least twice that to have real consequences in a dough," he told me. He also stressed that my testing exaggerated the effect since I left the flour open to the air for days on end. "Nobody stores their flour in an open container," he said, suggesting the real-world consequences are going to be smaller than what I was documenting.

When I asked Andrew if, in practice, bakers would ever worry or notice shifting dough humidity levels, he said mostly no. "It's just not something bakers think about, except in professional settings, where bakers will often tweak formulas for new *lots* of flour." It's a helpful observation that makes sense. When a large batch of new flour arrives at a bakery, that's a transitional moment in storage conditions, moving from where it had been to the bakery's own storage system. It will not acclimate immediately, given the amount of flour and the fact that it won't be left in the open air to equilibrate. It's one moment when professional bakers, who are highly attuned to their doughs, may want to make some adjustments. But overall, in the context of home baking, it's clear that outside of extreme conditions, the ambient humidity will not have a meaningful impact on a dough's hydration and the resulting baked good, and it's not something that requires in-the-moment adjustment.

Put another way, recipes that have you adjust the dough bit by bit do so not because of unseen environmental variables that need to be accounted for, but because the recipe itself is inexact—it doesn’t know what its target hydration is supposed to be.

But Wait, My Experience Says You're Wrong!

Some readers may be objecting at this point, because they have seen for themselves just what an impact ambient conditions can have on baking. Doughs can seem very different between a hot, humid summer and a cold, dry winter. This isn't imagined, it's real and confirmed by their experience. King Arthur Flour has a whole article on it, showing just how dramatic those effects can be, and advising to cut the water in a dough by as much as 10% to compensate for the higher humidity.

What gives?

Stella Parks, our dear former baking editor here at Serious Eats, has actually addressed this before. In her article on managing pie doughs in the summer heat, she wrote, "Folk wisdom says that humidity plays a role in how much water your dough needs, but I've gotta disagree. Flour has a fairly low capacity to absorb moisture from the air, and that very property is what keeps it stable on the shelf. If flour could suck up enough ambient moisture to change how a recipe behaves, it would mold as quickly as a loaf of supermarket bread."

Put another way: People are conflating the impact of temperature and humidity on a dough, and laying all the blame on humidity. According to Stella, controlling the temperature of not only your kitchen but your ingredients is much more important than trying to tweak hydration, and will lead to better results, since dramatic swings in hydration can have a lot of downstream effects on a dough, even if they seem to "fix" a problem with a dough.

Does that mean humidity has no role in any of this? No, I wouldn't dare go that far. But I would encourage everyone to look elsewhere for an explanation for why a dough seems too wet or dry—temperature, for example, or a larger formulation problem in the recipe—before assuming the humidity is the culprit. It probably isn't.