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I wish to make a declaration, and here it is – Monica makes better stew than I do. That’s because she unfailingly understands and implements the proper steps needed to separate a stew from a mere soup – She knows exactly how to thicken things up, and what to use in so doing – In other words, creating thick from thin.

Thickening is far more important to cooking than first glance might indicate. From baking to braising and sauces to stew, entire dishes, or critical components thereof, require a dependable thickening agent to turn out as expected. Let’s say you’re in the mood for pasta, and you want to keep things light. A pan sauce, made with stock, a little wine, a squeeze of lemon, salt and pepper would do nicely – Except that, as described, it won’t stick to pasta very well, and it will be watery – Not a very appetizing image. Add a touch of a decent thickening agent, however, and everything is transformed. The delicate flavors now have a stable framework to marry within, and your lovely pan sauce will stick heartily to your pasta. Three questions spring from this example – What are our options, how do they work, and which thickener works best for a specific application? Let’s find the answers.

In a word, what we mean when we say thickening agent, is starch. From flour to cornstarch, and arrowroot to potato starch, there’s a wide array of options for home cooks. In gnarly scientific terms, a starch is a polymeric carbohydrate, or polysaccharide – a really long chain of sugar molecules that most green plants use as a primary source of stored energy. These starches occur as really small granules for the most part, which is a big reason that they lend themselves so well to cooking. The ones that make their way into our kitchens come from cereals and tubers – Wheat, corn, potato, and cassava for the most part. Seaweed also gets the nod, although that’s not all that common in the home kitchen – Irish moss, carrageenan, agar, and eucheuma are common examples.

There are, of course, artificial versions as well, and if you eat the processed crap that lurks in the middle aisles of your local grocery, you’re eating those too – anything that reads ‘alginate’ is an industrially produced product, mostly seaweed derivatives, and variously labeled as a thickener, stabilizer, or emulsifier on product labels. Finally, the popularity of molecular gastronomy has lead to some hybridized versions of things that are actually pretty cool, and quite accessible to the home chef – More on those a bit later.

So, how do these little suckers work, anyway? The answer lies in the chemical properties of those long chains of sugar molecules when they’re heated. Thickening gone wrong in the kitchen is like hitting a deer in eastern Washington – There’s those who’ve done it, and them’s who are gonna. Almost without fail, what’s at issue is a failed introduction. The oldest and most common starches found in the average home kitchen are flour and cornstarch, and those two just don’t mix with cold liquids. Once you introduce a starch to something hot, the magic begins – The starch granules begin to swell almost immediately, absorbing water. Once they hit their saturation point, the granules burst, adding more of those long chain molecules to the mix, and serious thickening begins. The starch expands, acting like a net and gathering as much liquid in as it can, and you’ve got gravy. How hot is hot enough to make this tiny miracle work? Flour and cornstarch are rich in amylose, and that little beastie needs to be almost to a boil to really reach its prime, although they’ll begin to work above 140° F.

Tapioca and cassava flour, on the other hand, contain another starch, amylopectin, and they don’t need to get close to a boil to work well – And for the record, tapioca and cassava are not the same thing – Tapioca is extracted from cassava roots by washing and pulping, while cassava is the whole root, peeled, dried and ground, as we covered recently in a post. Similarly, arrowroot as a dried version of a tropical tuber, and may come from one of several varieties, including cassava. More on this a bit later.

While we’re discussing how and why starches work as thickeners, it’s important to highlight some things that will hinder the thickening process. Acids, like that lemon juice and wine in our pan sauce, (as well as Vinegar of course), will weaken the thickening power of starch – not critically, in most formulations, but enough that we should be aware of it. The other common cooks mistake is tossing starch straight into a hot liquid. As many have discovered, that dog don’t hunt all that well. What happens is a very rapid gelatinization of the outsides of each starch lump. This effectively traps the rest of the stuff, leaving lumps of thickening agent and an embarrassed chef. What’s better, (and proper, frankly), is to draw off a half cup or so of whatever you’re wanting to thicken into a measuring cup, add the starch to that, mix thoroughly with a fork, and then pour that into the dish in progress – Stir that in thoroughly, and you’re giving your thickener the chance it needs to do its thing.

Time to answer that third question – What are the various thickeners best at, and how should they be deployed?

First comes flour, the go-to for most home cooks. The first things we’ll do, then, is talk about why maybe you don’t want flour to be your go-to. The reason? Putting it simply, flour isn’t a pure starch, as many other thickeners are – There are other proteins and whatnot in there, so ounce per ounce, flour has roughly 50% of the thickening power of pure starches. That means that it not only takes more to do the same job, but you get definite taste, textural, and visual notes when thickening with flour that you may not always want. Flour works best for stuff that won’t suffer from those potential shortcomings – White sauces, like béchamel, stews, and fricassées, for instance, and of course nothing else will truly do in a roux.

If you’re going to use flour for thickening, I highly recommend investing in Wondra – You’ll find it in most stores, in a round, blue and white can – Wondra is a low protein wheat flour that is roasted and dried, so it’s kinda like the Uncle Bens of flour. Because of that, it doesn’t clump, and makes excellent gravy and sauces – Its also great for dusting stuff you’re going to fry – It makes a nice, light coating. How best to deploy flour? You can add it to your aromatics at the beginning of the build process for a soup or stew – It’ll combine with the oil you use to sauté those veggies, and effectively create a roux. You can also coat your proteins in it, and then brown them – That’s Monica’s preferred method and it works great. You can also add flour to a cup or so of whatever you’re wanting to thicken with good results. One important note – Just as you need to cook canned tomatoes or beans long enough to get the can taste out, so must you cook flour thickened dishes to get rid of the raw flour taste – 3 to 5 minutes minimum at a steady simmer will do the trick.

Next up, cornstarch. Derived from, yes, corn, it’s a pure starch and a potent thickener. It imparts fewer indicators of its presence than flour does, and it can stand up to quite a bit of cooking without losing power. Because of that, it’s great for cream pies and puddings that require fairly lengthy cooking times. The potential downside of cornstarch lies in the fact that it’s more prone to clumping than any other starch – combine it with sugar when baking, or to enough liquid to form a smooth paste before introducing it to the main dish, to counteract its desire to clump. Cornstarch also provides a clearer finished product than flour – Something to keep in mind when appearance matters, (and when doesn’t appearance matter?)

Tapioca, which is extracted from cassava roots, can be found in pearl and powder form. It has, for my mind, a pretty narrow window of use. It’s great with fruit pies, jams, and jellies because it gels up more firmly than other starches, and holds a lot of liquid, and those qualities can really help keep a sweet treat from getting soggy. That said, it can be quite overwhelming, even cloying, hence the narrow window of opportunity. Note that tapioca does not do well on baked goodies with an open or lattice top, because it will not dissolve well when so deployed – With any pie, it’s a best practice to let the tapioca marry with the fruit for a good 10 minutes prior to baking. It’s also not great for soups and stews because it tends to break down quickly when exposed to relatively long cooking times.

Arrowroot is not widely used as a thickener, though it sure was back in the day – The earliest cultivation evidence for this stuff goes back over 7,000 years – It is enjoying somewhat of a comeback lately. Arrowroot is a favorite for its light footprint and formidable thickening power. Arrowroot comes from several rootstocks – Maranta Arundinacea or Manihot Esculenta, (AKA Cassava) in the tropics, Zamia integrifolia (Florida Arrowroot), and Pueraria Lobata, AKA Japanese arrowroot, also known as the dreaded Kudzu vine. The only no-no for this stuff is use with dairy – doing that will result in a most unpleasant, slimy consistency.

Otherwise, arrowroot works faster and more efficiently than either flour, cornstarch, or tapioca. It will thicken at a lower temperature, and won’t make clear stuff cloudy. You can even freeze stuff thickened with arrowroot, something no other options does very well at all. You can substitute 2 teaspoons of arrowroot in recipes calling for a tablespoon of cornstarch, and 1 teaspoon for those asking for a tablespoon of flour. When you use arrowroot, add it to warm liquid and mix well prior to introduction to a hot dish. As soon as whatever you’re working on thickens, remove it from heat, as arrowroot has limited tolerance for long cooking, (As such, it’s not what you want to use for pies, tarts, etc). Arrowroot has excellent resistance to the weakening effects of acids, so those soups, stews, and sauces with citrus, wine, or vinegar are prime turf for its use.

Potato starch is another thickener that you’ve not seen much in this country until recently, though it’s always been popular in Europe. Derived from, yep, potatoes, its recent popularity here is due to the fact that it’s one of the latest crown princes of the gluten free/super food hype parade. Beyond that, it’s another one I like a lot. Bob’s Red Mill makes great potato flour and starch, and is widely available. Potato starch is highly refined, meaning it has very little protein or fat in it – This yields a thickener with a truly neutral taste, great strength, fast action, durability, and most impressive clarity – That stock, wine, and citrus pan sauce we started with comes out beautifully with potato starch onboard.

And then there’s that molecular gastronomy stuff. Poke around a place like Molecular Recipes, where I like to get my stuff, and you’ll find a raft of thickeners. All those industrial thickeners I mentioned a while back are here, if that sort of thing floats your boat. There are also elegantly refined versions of more traditional stuff, like the product they call Ultra Sperse. This is a highly refined version of corn starch – So much so that you can add it to almost anything, hot or cold, and it will thicken quickly, robustly, and without making lumps. Ultra Sperse yields a clean tasting, clear, bright thickened product you can cook to your hearts content, or. Ore to the point, not if you prefer or need to do things cold. It’s amazing stuff, and I highly recommend it. THE USUAL DISCLAIMER – No, I don’t work for or with this outfit, nor do I get free or discounted stuff from them. I bought it, with my money, same as you can, and I recommend it because it’s great stuff you’ll like too.

And finally, never forget the power of leftovers – Case in point, we’ve just had thanksgiving, which lead to the full blown turkey and all the trimmings dinner. On day three, I made turkey stew, and thickened it with leftover gravy and mashed potatoes. It was stunningly rich and delicious. And of course gazpacho, that heavenly cold soup, absolutely must have day old bread used as the thickener – Anything else would be uncivilized. And a little corn flour is the bees knees in your next batch of chili.

So there you have it, some new stuff to go find and try, and a solid reference for future explorations.