Chances are, unflavored gelatin isn't something you think about very often, except when grabbing some Knox powder at the store. And, for the most part, that's a-okay; when used exactly as directed, gelatin's a pretty straightforward thing. But the more you bake, the more likely you are to venture outside the box and experience some sort of mishap. Say, a rubbery panna cotta, sticky marshmallows, or a droopy chiffon pie.
It's absolutely maddening to stare at a recipe and have no idea what went wrong, especially if it seems you followed the directions to a T. Having worked with sheet gelatin in restaurant kitchens and powdered gelatin at home for the better part of my life, I've witnessed more of those trials and tribulations than most. That has led me to realize that these failures aren't random, and that some pretty benign circumstances may create problems for gelatin.
What Is Gelatin?
Let's make sure we're all on the same page here first. Gelatin is a protein extracted from animal sources. Bloomed gelatin is melted and incorporated into a dessert, dispersing little molecules of protein throughout. As the gelatin cools to below 100°F, those molecules begin to interlink, reorganizing themselves into a three-dimensional net, with water caught inside. That reduces a dessert's ability to flow, giving mousse or panna cotta a relatively firm texture despite a high proportion of liquid ingredients.
Many of gelatin's most surprising quirks are side effects of its manufacture. Contrary to urban legends, gelatin doesn't come from hooves (which are made of keratin) but from collagen-rich hides and bones. While gelatin can be made in a number of ways, from a commercial standpoint, we're talking mostly about pork hides and cattle bones—disparate sources that require different processing techniques. An acid treatment for hides, and an alkali treatment for bones.
As with olive oil, multiple rounds of processing can extract several different grades, the first being the finest. This sort of gelatin is valued for its light color, mild flavor, and high molecular density, a measure of its strength. With each subsequent extraction, the resulting gelatin is darker, meatier, and less dense (i.e., weaker). As a general rule of thumb, porcine gelatin tends to be lighter in color but more aromatic, while bovine gelatin is darker but less fragrant.
After extraction, these various grades of porcine and bovine gelatin can be blended individually or with each other in exponential ways, then processed into granules or sheets. All those variables mean that gelatin's color, flavor, aroma, and strength can differ considerably from country to country or even brand to brand.
In and of itself, that's enough to explain why an American might have trouble adapting a French recipe (or vice versa), and why fancy restaurant desserts don't always turn out so well at home. It's also the reason why a seemingly innocent switch from one gelatin to another might be the source of all your woes. Beyond that, there are a number of other variables that can provoke gelatin to behave in unexpected ways. Here are six of the most pernicious, and what to look out for.
Issue #1: Bloom
The Scenario: A recipe calls for a specific type of gelatin, but it's not what you have on hand. Who cares; protein's protein, right?
Well, not really. Gram for gram, gelatin's mostly protein to be sure, but by blending different grades, manufacturers create a mix of proteins that behaves in a very specific way. Its behavior is expressed in terms of bloom—an obscure measurement of gel strength ranked on a scale of 0 to 325. As you might expect, the higher the number, the stronger the gelatin, but textural differences come into play as well. I'm not quite ready to start unpacking the mechanics of molecular density and interlinking protein chains, but high-bloom gelatins result in a tender gel, while low-bloom gelatins produce one that's gooey. So, while you can use more of one type or less of another to create a similar strength, you can't always re-create the mouthfeel of a particular gelatin. (Imagine a stretchy panna cotta, or a gummy bear that breaks like Jell-O.)
The Danger: Without taking into account differences of bloom, your recipe may be doomed from the start. The best way to avoid trouble is to hop online and buy the exact sort of gelatin a recipe calls for. If you're whipping up a dinner-party dessert and don't have that kind of time, it's important to realize that a rough 'n tumble substitution is no guarantee of success.
While bloom strength is rarely printed on the box, all you need to know is that powdered gelatin is formulated to an industry standard of about 230 in America and 250 in Europe, creating some unspoken implications depending on the citizenship of a recipe. Sheet gelatin is a little more complicated because it's sold in strip-club membership tiers (bronze, silver, gold, and platinum) that represent not specific bloom strengths but a range. For example, platinum gelatin can be anything between 235 and 265 bloom, so unless you match a recipe brand for brand, your results won't necessarily be the same.
Any recipe you find on Serious Eats is tested with Knox gelatin in mind, and, because I happen to have a pork allergy, my desserts are cross-tested with bovine gelatin as well. Ounce for ounce, my favorite brand costs a fraction of the price of its supermarket counterparts, and has a far milder aroma as well—bad news for savory applications, but great for dessert.
Issue #2: High Heat
The Scenario: For some reason, your marshmallows keep turning out gooey and strange, even though you followed the recipe precisely. What gives?
Back-of-the-box directions that call for boiling water give us the impression that gelatin is impervious to heat, but boiling simply represents its upper limit. Gelatin's strength rapidly declines above 212°F, or when it's held at that temperature for an extended period of time. Curiously, damage caused by heat impacts rigidity, not viscosity, which explains how gelatin can still add body to slow-simmered dishes like Bolognese. If sufficiently concentrated, even weakened gelatin can have remarkable power (as in a hyper-reduced veal stock turned glace), but that has no bearing on dessert.
The Danger: Unfortunately, few recipes will warn you of gelatin's vulnerability to heat (a reality compounded by the presence of acidic ingredients), so, without a cooling period, you may stumble into trouble unawares. This is particularly true of marshmallows, which involve a sugar syrup cooked to an excess of 250°F. Whether the recipe says so or not, it's best to let the syrup cool to about 212°F before adding the gelatin, or else the candy may have an unpleasantly soft or gooey texture.
Issue #3: Strong Acids (Low pH)
The Scenario: You've found a great recipe for lemon mousse that calls for Knox or kosher gelatin, but you've converted to another type or brand. Even though you were sure to account for bloom, something went wrong. Is the recipe a dud?
Maybe not! While recipes never specify bovine or porcine gelatin, any recipe that calls for Knox was formulated with the power of a blend. Meanwhile, kosher or halal recipes almost certainly use bovine (piscine, in some rare instances). Many other brands are strictly porcine, especially when it comes to sheet gelatin or powders sold in bulk online.
The Danger: The acidic treatment used to denature the collagen in animal hides leaves porcine gelatin vulnerable to solutions with a pH of 3 or below—on par with distilled white vinegar. Most desserts aren't that acidic, but ingredients like lemon, lime, passion fruit, rhubarb, and even pomegranate are. If the directions bring juice and gelatin into direct contact, extreme acidity creates a perfect storm of circumstances in which shifting from one type of gelatin to another may cause trouble, particularly in recipes that call for only a small amount of gelatin, like panna cotta or mousse. (Gelatin's vulnerability to acid can be overcome with sufficient concentration, as in gummy candies.)
If a recipe bothers to mention a specific brand or type of gelatin, it may be with good reason! That might not always be the case, but knowing that acidity can constitute a red flag when it comes to gelatin can help you avoid problems with an unfamiliar recipe.
Issue #4: Alcohol and Enzymes
The Scenario: You've found a recipe that calls for gelatin to be bloomed (hydrated) in vermouth, but that's not really your thing, so you decide to try a different liquor or fruit juice instead.
The Danger: Switching things up with the blooming liquid may seem like a creative opportunity, or at least a harmless swap, but there's some real potential for disaster. Not only do high-proof spirits deny the gelatin access to water for hydration, direct exposure to alcohol may denature the proteins altogether, rendering them useless.
Likewise, some plants contain protein-digesting enzymes that can destroy gelatin as well. These include fresh pineapple, papaya, kiwi, mango, and fresh ginger, so it pays to do a little bit of research before making any substitutions.
Issue #5: Time
The Scenario: You've got a recipe that works like a charm, but it doesn't always turn out the same from batch to batch. You've got the technique down pat, so what's going on?
Years ago, I noticed that my marshmallows occasionally turned out extra fluffy. I was at a loss to explain it, and stymied by the sheer number of variables in a commercial kitchen (from flavor to ambient temperature, et cetera), so, for a time, I just chalked it up to luck. Over the years, I eventually noticed that my best marshmallows were always the ones I prepped the night before, something I'd do in the busy season to get a jump on my morning chores. Check it out.
These pitcher-shaped marshmallows were made with identical ingredients, equipment, and cooking/cooling temperatures, but the one on the right started with gelatin I bloomed four hours in advance. Whoa.
On a certain level, we all understand that gelatin gets thicker with time. Jell-O is thin and watery when we put it in the fridge, gooey an hour later, then firm and jiggly an hour after that. What isn't so obvious is that those improvements to strength begin the moment gelatin is first bloomed. So, when I bloomed my gelatin the night before, my marshmallows benefited from its accumulated strength. It's a nifty trick, but not one I'd universally recommend.
The Danger: Some recipes use gelatin to aerate and stabilize a foundational element that's later re-whipped or folded with something else down the road (think: butter, cream, or meringue). Allowing bloomed gelatin to mature helps that base gain extra volume, but the added strength reduces its elasticity, making it difficult if not impossible to accommodate other ingredients later on. That's bad news for homemade marshmallow frosting, Bavarian cream, and even homemade Cool Whip—a recipe I'll tackle later this week.
Issue #6: Sugar
The Scenario: You can't believe how much sugar that recipe calls for! Surely it wouldn't hurt to dial things back.
I've said it before, and I'll say it again: Sweetness is sugar's least important role. Whether in marshmallows or in a simple fruit gelée, sugar competes with gelatin for water and alters the density of a solution, both of which can have a profound impact on gel formation.
The Danger: Lowering the amount of sugar in a recipe can speed gel formation, but it may also produce a softer set because, in the right amount, sugar can improve gelatin's rigidity. Sugar encourages gelatin to form shorter protein chains, creating tenderness in desserts, so cutting back can lead to seemingly gooier results.
If a recipe seems too sweet, the first and best course of action is to adjust the amount of salt. You can also tame sweetness by switching from plain to lightly toasted sugar, if you happen to have any on hand.
Suffice it to say, venturing off the beaten path with a gelatin-based dessert is a hit-or-miss proposition. Hopefully, understanding some of these conditions will shed a little light on past experiences and, more importantly, illuminate potential problems you may face down the road.