Humidity's Effect on Baking Ingredients

FRED QUESTION: Love your books and just discovered this blog. WOW! I'm a firm believer in weighing everything, but flour and brown sugar bother me. Since these two ingredients absorb water, how does humidity in the air affect their performance in recipes? In other words, does, say, 1 lb. of flour weighed on a hot and humid summer day actually contain less flour (and more water) than that weighed on a cold and dry winter day? How does a person compensate for this variation other than adding a little bit of flour or water at a time (which seems rather unscientific) as one goes along?

ROSE REPLY: actually the 2 ingredients you mentioned have similar problems as they tend to dry out if improperly stored. they both benefit from airtight storage especially brown sugar that gets very hard when dry. i store mine in canning jars and never have a problem but if it comes in other containers it will dry and then you'll need to put a little foil cup in with the sugar and set a paper towel that has been dampened in the cup and then cover the container tightly. in a few hours the sugar will become soft again. in very humid or very dry conditions the flour used for bread making will be affected but this can be controlled easily by adding a little flour or water to the dough if the consistency seems to require it. for cakes i don't find much of a difference. i do find a difference in salt that is so hygroscopic some days 1 teaspoon weighs 5.3 grams, other days it weighs 6.6 grams. but even that doesn't seem to make a noticeable difference in the baked product. in any case, the volume of the flour or the brown sugar will be affected by humidity as well as the weight and weight is always a more accurate way to go because measuring varies from time to time by factors far more significant than humidity!