经过David Joachim and Andrew Schloss
FromFine Cooking＃132，第28-29页

Easy to use, easy to find, and able to assume the flavor and color of whatever liquid it’s dissolved in, gelatin is a versatile thickener for both sweet and savory cooking-it’s the secret to the shimmering glaze of a perfectly reduced pan sauce and the silky mouth-feel of an ethereal panna cotta. Mix gelatin with liquid and heat it up, and it dissolves into a thin, clear, flawless sauce; let it cool and the liquid firms up into a jewel-like solid. But as soon as that solid hits the warmth of your mouth, it becomes fluid again. Here, we’ll explain where this magical ingredient comes from, the science behind how it works, and how to successfully use it in your cooking.

明胶从哪里来？
Gelatin is a mild-tasting protein derived from the collagen in animal tissue, and it’s the only protein with the power to thicken liquids. You can see its effect every time you roast meat. The drippings in the bottom of the roasting pan owe their slightly sticky consistency to gelatin. That viscosity allows you to boil those juices into a luscious sauce without the addition of any other thickener. It’s also why the juices set into a solid gel as they cool. Unlike starch- and flour-thickened sauces that are opaque and creamy, sauces thickened with gelatin are crystal clear and syrupy.

Most gelatin is produced from pig skin, which contains about 30% collagen by weight. Collagen is the connective tissue protein that gives strength to muscles and tendons and resiliency to an animal’s skin and bones. To make gelatin, pig skin is soaked in dilute acid for about 24 hours, which unravels the crosslinking protein bonds in the collagen. The resulting free protein chains are extracted, filtered, purified, and dried into sheets or granules (powder) that are around 90% gelatin, 8% water, and 2% salts and glucose.

明胶如何工作？
Gelatin is unlike any other protein used in the kitchen. Typically, food proteins respond to heat by unraveling, then bonding to one another and coagulating into a firm, solid mass. For example, think of a frying egg. The liquid protein of the white, called albumin, firms up into a solid mass of egg white as it heats. But gelatin proteins don’t readily form bonds with one another. Heat causes them to initially unravel and disperse just like any protein. They never form new bonds, though, so the liquid in which they’re dispersed stays fluid. Because gelatin proteins are long and stringy, they tend to become interwoven, causing the hot liquid in which they are suspended to thicken, but not completely solidify when warm. As gelatin cools (as in a pan of cooled meat drippings), the protein strands line up next to each other and twist into long ropes, transforming the liquid into a firm gel.

How should gelatin be handled in the kitchen?
首先，将明胶浸泡在冷水或其他冷液中，以补充其干蛋白网络，使其易于溶解。（如果将明胶直接添加到热液体中，它将粘在一起并形成团块。）浸泡后，只需加热水/明胶混合物（或加入热液体），然后搅拌以溶解明胶即可。明胶具有吸湿性（它很容易吸收并保留水），因此最好将其存放在干燥的容器中，并在干燥，通风的区域中。当以这种方式存储时，它具有不确定的保质期。

薄板和明胶粉有什么区别？
Chefs generally prefer sheet gelatin to powdered gelatin because sheet gelatin has less surface area, so when the hydrated sheets are stirred into the hot liquid, less air becomes incorporated, creating better clarity in the finished gel. Sheet gelatin isn’t as readily available as powdered, but you can easily substitute powdered for sheets using this equation: 4 gelatin sheets = 1-1/4 oz. envelope (2-1/2 tsp.) powdered gelatin. That’s enough to lightly gel about 2 cups of liquid, creating a 1-1/2% gelatin solution, which is perfect for savory sauces and glazes. For a firmer effect, such as that in a typical gelatin dessert, use the same amount of gelatin to gel 1 cup of liquid, creating a 3% gelatin solution.

Are there vegetarian alternatives to gelatin?
是的。明胶的素食替代品是由碳水化合物而不是蛋白质制成的。最常见的素食胶凝剂是琼脂（又名Kanten）和角叉菜胶（又名爱尔兰苔藓），它们都是从红藻（Red藻类）中提取的，这是一种海藻。

受欢迎的亚洲烹饪和广泛使用health food stores and Asian markets, agar works much like gelatin in that it’s soaked in cold water and dissolved in hot liquid, which then firms up into a gelled solid upon cooling. The main difference for the cook is that gels made with agar must be boiled to completely dissolve the carbohydrates, whereas gels made with gelatin actually weaken if the mixture is boiled. The other difference is that while gelatin melts near body temperature (95°F to 100°F), agar melts at about 185°F, so agar gels will not melt into a tongue-coating liquid in your mouth. Agar gels also tend to have a more fragile and crumbly texture than gelatin gels. However, agar has an even greater gelling capacity than gelatin-you need only about 1/2 teaspoon of agar powder to firmly gel 1 cup of liquid as opposed to 2-1/2 teaspoons for powdered gelatin.

Carrageenan (Irish moss) has a unique property: It can thin under pressure, yet return to its original viscosity once the pressure is released. For this reason, it’s often used in industrial food production, where it can be pumped through factory pipelines without losing its thickening ability. It’s a preferred thickener for ice creams and bottled sauces.

There are three classes of carrageenans: kappa, iota, and lambda. Kappa carrageenans produce firm gels; iota carrageenans produce softer, more elastic gels; and lambda carrageenans gel only when mixed with proteins, such as those in dairy products.

Some studies suggest that carrageenans may result in the development of gastrointestinal inflammation; however, the Federal Drug Administration and the National Organic Program currently consider carrageenans safe for human consumption.

与明胶一起工作的提示

• 避免在高热量或长时间内加热明胶，这两者都会削弱其胶凝能力。最好将溶解的明胶添加到已经煮沸或煮熟的液体中。将酱汁加厚的调味料加固，以避免降低凝胶，这也是如此。
• 咸或酸性成分倾向于软化凝胶，因此与它们一起使用时可能需要使用更多的明胶。
• 糖或奶油有助于凝固凝胶。糖具有吸湿性，并从明胶分子中抽水，增强其胶凝作用，而乳霜使混合物更粘稠，从而使混合物的整体变稠。
• Avoid freezing gelatinthickened liquids, which causes liquid to seep from the gel when it is thawed.
• 某些新鲜成分 - 桃子，菠萝，木瓜，芒果，瓜，猕猴桃，无花果，刺梨和姜汁含有称为蛋白酶的酶，可消化明胶中的蛋白质。结果，用这些新鲜成分制成的凝胶可能无法正确变稠。要中和酶，请在使用明胶甜点之前将切割成分煮沸5分钟，或使用罐头水果（在罐装过程中已加热）。
• 要将固体悬浮在凝胶中，请让凝胶冷却直至半比率，然后再搅拌固体。
• 要从杯子或装饰模具中释放冷的凝胶，请将杯子或模具浸入温水中5至10秒钟，以重新固定凝胶的外边缘，然后通过摇动或使用薄刀和倒转来松开边缘。