The Plot Thickens (A Hydrocolloid Story)
Dave Arnold - January/February 2008
Their lab science name could scare chefs from using substances that are becoming essential to an updated culinary toolkit, no matter the cooking style. David Arnold, head of The French Culinary Institute's culinary technology department, cuts through a thicket of terminology and techniques to humanize hydrocolloids.
Without the éclat that awoke a startled food world to foams a decade ago, hydrocolloids have quietly insinuated themselves into the kitchens of many of the world's most highly regarded chefs, most notably in the innovative dishes dreamed up by the likes of Wylie Dufresne (WD-50, New York City) and Grant Achatz (Alinea, Chicago). The product names sound straight out of the laboratory—xanthan gum, carrageenan, guar—but almost all hydrocolloids are completely natural. They've gotten bad reputations as back-of-the-label additives used for economy's sake; for decades they've been used to make food cheaper and easier to produce, ship, and store, and they have facilitated the removal or reduction of "real ingredients" like fat and dairy. But today chefs are using hydrocolloids to make food better, not easier to prepare.
How "better?" Hydrocolloids allow chefs to take any pure flavor and, by adding a small amount (typically less then 1 percent) of a tasteless hydrocolloid, achieve any texture or consistency desired. Take a sauce. Thickening it by reduction alters its taste; thickening it with cornstarch or flour masks flavor, alters appearance, and requires heat. By adding a very small amount of xanthan gum instead (1 gram per 500 grams of sauce) the sauce gains the desired body with no effects on flavor or look and without any heat, a much more precise way to thicken it. Thickening sauces with flour or cornstarch is like trying to use a baseball bat to do the job of a knife. Hydrocolloids are not miracle workers in themselves; they must be paired with a cook who knows how to use them. Adding too much xanthan gum to a sauce, for example, will produce an unappetizing slime.
Starting out with hydrocolloids can be daunting. Don't try to tackle all the hydrocolloids at once. Pick a couple, use them until you feel comfortable using them, then branch out. Here is a brief guide:
What are hydrocolloids? Hydrocolloids are ingredients that interact with and control water. They are almost always in the form of white or cream-colored powders. With the exception of gelatin, a protein, hydrocolloids are just complex sugars. All sugars are made up of units called monosaccharides. Sucrose (table sugar) has two units of monosaccharides. Hydrocolloids have thousands of units arranged in long chains that interact with themselves and with water to thicken and to form gels. Most hydrocolloids come from simple natural sources like seaweed (carrageenan, agar-agar, alginate), seeds (locust bean gum, guar gum), tree sap (gum arabic), fruit (pectin), and microbes (xanthan gum, gellan). These ingredients are purified forms of naturally occurring substances in the same way that refined sugar is the purified product of sugarcane or sugar beets. Many hydrocolloids are traditional ingredients that have been used for hundreds, sometimes thousands of years. A few hydrocolloids, like methylcellulose (a modified form of cellulose) don't occur naturally. But that doesn't make them harmful.
What will I need to get started? An accurate scale. A scale that measures to within one gram will suffice to start but one that measures to within 0.1 gram is better. Very inexpensive battery operated pocket scales abound on eBay.
Some blenders. Immersion (stick) blenders are very useful for mixing powders into liquids. For many applications, however, a high-powered mixer is necessary to get a lump-free product in a reasonable amount of time.
Recipes. Find good recipes, follow them exactly, and keep meticulous records of your experiments. Steps that seem trivial, like where in the recipe a hydrocolloid is added, can mean the difference between success and failure. Good recipes will also specify what product is being used, preferably down to the brand name. Methylcellulose, for instance, is marketed by Dow under the name Methocel in over a dozen varieties that are all very, very different. A recipe that calls for methylcellulose is useless; a recipe that calls for Dow Methocel F50 is not. Avoid imprecise recipes, as they are a prescription for failure.
A hydrocolloid supply. Some hydrocolloids are easily found—agar-agar is in most Asian markets and xanthan gum is available at health food stores because vegans use it as an egg substitute. Try not to use cheap "vitamin grade" hydrocolloids, like health-store alginate because they just aren't predictable enough. Many industrial suppliers will send you samples of hydrocolloids if you ask, but most aren't set up to deal with small orders (under 50 pounds, which is more than a lifetime supply for most chefs). Companies like Terra Spice (www.terraspice.com), Le Sanctuaire (www.le-sanctuaire.com), and Ferran Adrià's (of El Bulli) Texturas (www.texturaselbulli.com) are better sources for the individual chef.
More information. If you want to go beyond following recipes, you'll need to do some research. Unfortunately, most of the books on hydrocolloids are dense, expensive, and of little use to the chef. I can only recommend Hydrocolloids by Andrew C. Hoefler, from the Eagen Press Handbook Series. Happily, the manufacturers themselves provide loads of free information on the Web. Additionally, courses on the subject are beginning to be offered at cooking schools.
Hydrocolloids can be roughly grouped into two types: thickening and gelling. Thickeners are classified by the type of flow they produce. Most hydrocolloid solutions are shear thinning, meaning the harder you stir them the easier they are to stir. This is because, at rest, hydrocolloid molecules form a tangled mess, but when stirred hard these molecules tend to line up in the direction of flow and slip past each other. Besides being shear thinning, some hydrocolloids, most notably xanthan gum, possess a yield point. A solution with a yield point doesn't act like a liquid at all until a minimum amount of force is applied to it. Instead it acts like a gel. After enough force is applied to overcome the yield point, the solution immediately thins and begins to act like a liquid. This feature is what makes xanthan gum so useful for applications like salad dressing, where it acts like a weak gel stabilizing the oil drops that have been beaten into the vinegar but allows the dressing to be poured like a liquid.
Gelling hydrocolloids are more complicated to assess. It's vital to know how and when a hydrocolloid gels. Gels like gelatin, agar-agar, and carrageenan are formed by cooling. These thermo-reversible gels can be set and remelted again and again. Gelatin takes a long time to set and melts and sets at roughly the same temperature. Agar-agar is fast-setting, and it sets at a much lower temperature (around 95°F/35°C) than it melts (around 185°F/85°C). This difference in temperature, called a temperature hysteresis, is very useful for the cook, as agar-agar gels can be served quite hot. Some hydrocolloids, like gellan gum, form gels when cooled but can't be melted again; they can be heated to the boil. Methylcellulose is the only hydrocolloid that forms a gel when it is heated and melts as it cools, useful industrially to prevent pie fillings from boiling out during baking and to keep barbecue sauce on pieces of grilling chicken. Hydrocolloids like sodium alginate, certain pectins, and some types of gellan solutions don't care about heat but form gels in the presence of calcium. Alginates in particular are useful for the "caviar" tricks so popular these days: alginate solutions are dropped into a bath containing calcium (calcium chloride, calcium lactate, or calcium gluconate), where they immediately form gelled beads with liquid centers. But keep in mind that these beads keep gelling after they are removed from the calcium bath and will eventually become solid.
You'll also need to understand a gel's texture and flavor-release properties. Gelatin is favored by many chefs because people like its texture, and it has good flavor release because it melts around body temperature. Other gels, such as most alginates, are very rigid and provide poor flavor release, the downfall of many "caviar" dishes. Many very brittle gels, like agar-agar, provide good flavor release because they break up well in the mouth. Sometimes gels are too brittle but can be modified to make them very useful. For instance, locust bean gum, a thickener, can be added to kappa carrageenan to form a gel that stores well in a hot kitchen, contains no animal products, and sets quickly with the good texture and flavor profile of gelatin.
What do the names mean? Gelatin. This is the only hydrocolloid that is a protein and the only one derived from animal products. Gelatin clarification is a new, very useful technique. Almost any juice or stock can be clarified using gelatin. Weigh the amount of product to be clarified and measure out 0.5 percent of that weight in powdered gelatin. Dissolve the gelatin by stirring it into a small portion of cold product and heating until dissolved; add the gelatin mixture back into the remaining product and freeze in a hotel pan. After it freezes, unmold it into a cheesecloth-lined perforated hotel pan and put it in the refrigerator to drain. What drips through the cheesecloth as it thaws will be perfectly clarified. It takes a couple of days to complete the cycle, but the results are fabulous.
Carrageenan. Derived from seaweeds, it's been used as a traditional ingredient under the name Irish moss. Chefs usually use the iota and kappa types, both of which form heat reversible gels. Kappa is brittle, while the iota is good at softer, more custard-like products. Both types have a pronounced synergistic reaction with milk; you only need one-fifth of the carrageenan required to set a water-based product to set a milk-based product. A good supplier is CP Kelco (www.cpkelco.com).
Agar-agar (a great beginner's choice). A traditional Asian ingredient derived from seaweeds. It forms a rigid brittle gel with good flavor release. It can be found in Asian food markets, and it's one of the few hydrocolloids where brand is not important. To use agar-agar, stir the powder into cold liquid and heat while stirring almost to the boil; the agar-agar will dissolve. The agar-agar will set as it cools to about 95°F/35°C and will not melt again unless heated above 185°lF/85°C. One of our favorite agar-agar tricks at The French Culinary Institute is making fluid gels. A fluid gel acts like a gel when at rest but like a liquid when agitated (similar to a yield-point thickener). Agar-agar can be used to make thick fluid gels that look like a puree on the plate but eat like a sauce in the mouth. Weigh the total amount of sauce, then measure out 0.8 percent of that weight in agar-agar and make an agar-agar gel as described above. After the gel has set, put the gel in a blender and blend on high until creamy. For a thicker fluid gel, increase the percentage. For a thinner product, decrease the percentage or add liquid to the finished product.
Sodium alginate. This is used to make the caviar beads that are many a chef's first foray into hydrocolloids. Alginates come from seaweed and form rigid nonreversible gels in the presence of calcium; they often have poor flavor release and don't break up well in the mouth. Alginate is very fussy about calcium, and you have to ensure that any calcium in your product is controlled with a sequestrant, or calcium blocking, compound. Sodium alginate also has a problem working with acidic products. A complete explanation of the process is beyond the scope of this article, but an explanation can be found on the Texturas Web site.
Propylene glycol alginate. This nongelling alginate derivative has become very popular as a thickener because it can be purchased in a variety of viscosities, is fairly acid tolerant, and doesn't react with many other gum systems. A good source is ISP (www.ispcorp.com).
Methylcellulose (a great beginner's choice). Derived from modified cellulose, it's sold by Dow under the trade name Methocel (www.dow.com/methocel/food/index.htm). There are many types available, all of which gel when heated. Some of the Methocels, Methocel F50 in particular, also act as whipping agents. F50, after being blended at high speed to hydrate, can be whipped like egg whites in a stand mixer to fluffy peaks. If this foam is placed in a dehydrator at 145°F/63°C, the Methocel will form a gel that supports the foam as it dries to a crispy, delicious, meringue—all flavor, no egg white. Use between 1 and 1.5 percent Methocel F50 by weight.
Pectin. Derived from fruits, usually apples or citrus rinds, they are familiar as the substance used to set jams. These traditional pectins (high methoxy pectins) require lots of sugar and acid to set. Low methoxy and low methoxy amidated (LM and LMA) pectins don't need lots of sugar and acid but use calcium to set, like alginate does. Pectin is known for its excellent flavor release and texture properties. A good supplier is CP Kelco (www.cpkelco.com).
Gellan gum. A product of microbial fermentation, it has very good flavor release and forms gels in very low concentrations. It comes in two varieties: high acyl (elastic and rubbery) and low acyl (hard and brittle). The two can be mixed to obtain intermediate textures. Low acyl gellan requires calcium to set. Gellan gels can be heated to the boil. Like agar-agar, gellan can be used to make fluid gels, but gellan excels at very thin fluid gels that act like soups or drinks. These fluid gels can be used to suspend bits of herbs or cubes of flavored gel. Gellan is produced by CP Kelco (www.cpkelco.com).
Xanthan gum (a great beginner's choice). This wonder gum is also a product of microbial fermentation. A little pinch goes a long way toward adding body to a sauce or stabilizing a dressing or foam. You will rarely use more than 0.5 percent, typically half that amount. Too much xanthan gives sauces a slimy, jiggly, unpleasant look and mouthfeel. Unlike most thickeners, xanthan gum has almost the same viscosity hot and cold, making it simple to use. It's also fairly easy to add to sauces—just use a stick blender or whisk to hydrate. Xanthan gum is unaffected by acids and moderate levels of salt. Available at health food stores.
Locust bean gum (LBG). A traditional thickener derived from the seed of the carob tree, it's also known as St. John's bread. To use locust bean gum, stir into cold liquid and heat the liquid almost to a boil. The product will thicken as the LBG hydrates. Good sources: CP Kelco (www.cpkelco.com) and TIC gums (www.ticgums.com).
Tips and pitfalls Hydration. All hydrocolloids need to be hydrated to work properly. Many hydrocolloid failures come from improper hydration. Hydrocolloid molecules are hydrated when they are completely surrounded by water and are in solution. If you simply add a hydrocolloid to a liquid, you will typically get lumps that won't dissolve. Hydrocolloids need to be dispersed before they can be dissolved, and there are two basic ways to achieve this dispersion: blend the hell out of a mixture (this is called high shear) or add the ingredient when it does not want to dissolve and then change the conditions so it does want to dissolve. To explain this counterintuitive concept, consider what you already know about cornstarch: if you add starch to a hot sauce you get lumps; if you add it to a cold liquid and stir while heating, you don't. The other important thing to remember about hydrocolloid hydration is that they prefer to be dissolved in pure water or as close as you can get to pure. For instance, if a recipe has a liquid with added sugar, hydrate the hydrocolloid in the liquid before adding the sugar. Sometimes a hydrocolloid will not hydrate in a given liquid because it's too acidic or too salty. In these cases, a recipe often can be saved by dissolving the whole portion of the hydrocolloid in a small portion of pure water and adding that to the problem liquid.
Synergy. You can't just add different hydrocolloids to each other and hope for the best. Many hydrocolloids will magnify effects when mixed, while others cancel each other out or produce completely novel effects. For example, locust bean gum and xanthan gum, both thickeners, will form a heat-stable gel when mixed. One of the things that separates masters of hydrocolloid use from other chefs is a knowledge of the possible synergies that can only be obtained by years of experience and observation. Some companies specialize in mixing hydrocolloids for specific purposes—they do the thinking for you, and the master of that field is TIC gums (www.ticgums.com). The company won't reveal the proportions of the ingredients in the mixes, but its product range is extensive and its technical support is outstanding.