GF Substitutions Part VII: All About Starches

by Jenn on August 24, 2010

in GF Substitutions,Gluten Free

Welcome to the next installment of Gluten Free Substitutions here on Jenn Cuisine!  We are now really getting into the nitty gritty of gluten free ingredients, last week covering binding agents, and this week moving on to the starches.  I think you’ll find this week is a bit easier, less complicated chemistry, hopefully :) The binding agents really did need chemistry though, because their main purpose in GF baking is to replace the missing properties of gluten.  Starches also can have some binding properties, albeit to a lesser extent.  I promise to keep the chemistry a bit less this week…we’ll see how I do 😉

Typically isolated starches, mostly or completely devoid of protein content and almost flavorless, can dissolve in water when heated, which is great for sauces that you want to be thickened, but you don’t want any flavors from the flour – or maybe you want a clear gravy.  Flours often have some starch content but also have other things as well (like protein!).  Often in GF baking recipes there is a starch listed in the ingredients, so I thought it’d be good to take a look at exactly what that starch part is – is there a reason for using a pure starch in your GF flour mix?  What exactly is the purpose of starch anyways? Here, let’s take a look at two extremes – tapioca starch and white corn flour – (And yes, I have a beaker for a measuring cup, I am a full chemistry nerd!).  Tapioca starch is clearly a starch, where as the white corn flour is indeed a flour.  Corn does contain starch, but it has to be extracted out of the corn to get pure cornstarch.  Here, I’m just talking about the flour – just finely ground up corn.

First, I added water to see what happens.  Side by side it looks like the corn flour dissolved better – see how much clearer the water is?  But look closely, and you’ll see that it pretty much all settles out to the bottom.  However, the tapioca is white like milk.  We find that the corn flour stays completely gritty if one reaches their hand in and tries to pick up the flour bits, where the tapioca mix feels like liquid only.

White corn flour in water:

Corn Flour

And tapioca flour in water:

Tapioca Starch

But don’t be fooled, actually neither dissolved! My tapioca starch is much finer than the corn flour, so the little particles have no problem floating around throughout the liquid (called suspension) where the heavier corn flour particles just sink to the bottom.  So neither really dissolve well in cold water.

OK, so now comes the fun test – what happens when we heat them?  First, the corn flour – upon heating and then cooling, the flour/water congeals to what looks like a precursor of porridge….

Corn Flour

And while it certainly has thickened, there’s no real gooeyness – if you pick it up with the spoon it just breaks apart from itself.  There’s not much really trying to hold it together.  Now I did the same with the tapioca – Upon heating, the tapioca all dissolves and turns clear and is a bit gelatinous.  See those air bubbles trapped?

Tapioca Starch

I did the same with sweet rice flour too, which is also very starchy.  When heated, it turned to a whitish/gray goo instead of clear, and I don’t think it was quite as gel-like compared to the tapioca.

Ok, I know what you’re thinking – “Thanks for the science lesson and all….but what does this have to do with my gluten free baking?” Alright, I admit it’s not so obvious just yet – but take another look at the tapioca starch concoction.  Look at how thick it is – see how it’s rounded up near the bottom of the spoon?  That shows surface tension and viscosity – And when you pour it from the spoon you get an “ooze” that slowly falls off the spoon to the bottom on one long strand.  Oh I know that sounds so appetizing, ha!  But those properties are there when you bake, and are part of what helps things stick together.

Tapioca Starch

But starches are not as strong as the gums or other binding agents.  And add too much of them, and you end up with a gooey mess.  Don’t make a cake with only starch.  It won’t be pleasant.  However, when I make gluten free pasta by hand (especially if I am going to be molding it and stuffing it), I have a very high starch content in my flour mix in order to keep the dough together: about 75/25.  But usually there is no hope for reheating the next day, because after a night in the fridge it has definitely congealed into a rather unattractive impossible to separate glob of goo (though I have had good luck freezing before cooking).   However freshly cooked, no problems, quite exquisite.

When I am making a GF recipe, I think about my starch:flours ratio.  Usually for goods such as breads, muffins, any type of dough (besides pasta) really, I aim for about 1:2 starch:flours – that means about 1/3 of my GF mix for a particular baked good is made up of a starch.  Then I tweak from there, depending on how things are going.  I have no idea if this is a normal amount, it’s just what I’ve tended to use.  If Michael Ruhlman could write a 2nd version of his best-selling Ratio book for gluten free recipes, I would love to see what the ideal ratios of flour mixes are for each type of good.  Is there a ratio of starch:flours that works best for you?  Have you found the amount of needed starch to change depending on what you are making?

So which of those gluten free ingredients are starches? I’ve typically come across five:

• Tapioca starch
• Potato Starch
• Arrowroot Powder
• Corn Starch
• Glutinous Rice

Is one starch better than another in certain situations? Maybe.  Def. in sauces/cooking applications they have differences.  But when it comes to baking, I’m not really sure.  In my experience I haven’t really noticed a difference between using one or the other.  But then, my baking experience is not so comprehensive as of yet.  We typically use tapioca, because I can buy it cheaply at our local Asian foods store.  We’ve tended to stay away from corn starch because of my father-in-law’s corn issues – not sure if the corn starch would affect him, but better to play it safe and use something else.  Maybe some of you more experienced GF bakers can chime in here: Does the end-quality depend on which starch you use in a recipe?  Are there reasons why you prefer one over the other in baking?