One of the most important properties of a gluten-free flour undoubtedly is its water absorption capacity. It's especially important in gluten-free bread baking; hydrocolloids (gluten replacers), need A LOT of water to properly activate. And that's why many gluten-free bread recipes have hydration over 100% (compared to ~60% for regular breads).
Water absorption capacity is a function of the flour's chemical makeup: do its proteins have hydrophobic or hydrophilic ends, is its starch content native or damaged, what about ash content, or fiber and so on.
I have read A LOT of papers about the water absorption capacity of gluten-free flours, and what I have come to understand, is that it is a hard thing to quantify with a number (though you can look at this peer reviewed paper for some water absorption numbers, and a great explanation). The problem is that not one paper has quantifiable data for ALL the gluten-free flours. Furthermore, the absorption capacity of flours is going to change based on the brand, the specific strand of grain (eg: ivory teff vs brown teff), how finely milled the flour is (finer flours have more surface area to absorb water), and even how humid the environment is.
So instead, I have decided to use a qualitative rating for water absorption: high, medium, low. Before I dig into my experiment, I want to give a shoutout to The Coconut Mama blog, who has a great post about water absorption of gluten-free flours, which I found helpful when comparing my experimental results and building my Ultimate Gluten-Free Flour Guide.
Water Absorption Experiment
Let's take a look with a nice visual. In each glass, there is 30 grams of flour mixed with 130 grams of water. I gave each glass a good stir with my cute chopsticks, and let the slurry settle for 10 minutes. On the image to the right, you can see that the glass containing rice flour has more "free water" sitting at the top of the slurry, while the glass containing cassava flour has less. From this, we can say that cassava flour has a greater ability than rice flour to absorb water. Repeat this experiment with all the 27 flours listed in my Ultimate Gluten-Free Flour Guide, and we have a good idea of each flour's ranking for water absorption capacity.
Water Absorbtion In Practice
What does this mean for us as bakers? Well, if I bake with rice flour, my dough--or my batter--is likely going to feel more wet than if I were to bake the same recipe with cassava flour. That's because rice cannot absorb as much water as cassava. As a recipe creator, I know that if I use cassava flour, I likely need to increase the recipe's hydration because cassava is "thirsty". We know that gluten-free breads require high hydration to activate the hydrocolloids (gluten replacers), and so in order to maximize my recipe's hydration ratio, I would want to bake breads with highly absorbent gluten-free flours. If I instead use flours like tigernut or sorghum, I may need to decrease the amount of water I use (as to not make a soupy dough!) and this could lead to our hydrocolloid friends not functioning optimally.
Furthermore, as a cottage food baker, I am always thinking about ways to increase shelf life. Water activity is a huge factor for the shelf life of a product. Water activity is basically the fraction of water in a baked good that is "available" for biological processes of bacteria/mold--in other words it's water that is not hydrogen-bonding with other ingredients. And so baking with flours that absorb a lot of water (in other words flour that easily forms hydrogen-bonds with water) leaves less "free water" for bacterial growth. And that's good, because our bread is not going to mold immediately!
Where My Blueprints Shine
Cool! But listen, I don't want you to think that high water absorption automatically means good. It's really about what you're trying to bake. Brownies and muffins may require less hydration, and so lower water absorption flours could be well suited there. Remember though, it's about knowing our ingredients, and consequently how to adapt our recipes (in this case, the amount of water) to suit our dietary choices. This gets kind of tricky for us as gluten-free bakers, since we usually bake with flour mixes! Fortunately, you will find that my recipe blueprints guide you in terms of water absorption. Here's an example, you're welcome!
Pastry Flour Mix Blueprint
- 25% Starchy/Low Protein Flour (typically white rice flour if possible)
- 33% Starch (with at least half being corn if possible, for a crispier pastry)
- 20% Medium Protein Flour
- 13% Milk Powder (taste and texture enhancer)
- 7% High Water Absorption Flour (to prevent product dryness)
- 2% Hydrocolloid (gluten replacer, binder)
If you want to keep geeking about water absorption, please check out this post by the Gluten-free Gourmand: she explains what's called the "tortilla test," which is a method that will let you find the exact hydration ratio of your flour (or flour mix) for bread baking!
Where do you go from here? Check out my Ultimate Flour Guide !
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