Cookbook:Gelatin

Gelatin
Gelatin
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Category	Thickeners and stabilizers

Gelatine or gelatin is an animal-derived substance used as a stabiliser or thickener in many foods.^[1]^[2]

Production

In simple kitchen setups, gelatin is simply produced by simmering (or otherwise slowly cooking)^[3] the skin, bones, and connective tissues of animals for an extended period of time.^[4]^[5] This process breaks down the collagen into gelatin,^[6]^[7]^[8] and cooling the resulting stock will yield a thick jelly-like substance.

Commercially, gelatin is produced slightly differently in order to maximize the yield and quality of the extracted product. Type 'A' gelatin is made by soaking the collagenous tissue in cold acid, which breaks down the collagen into gelatin.^[9] The gelatin is then extracted with warm to hot water in successive extractions.^[9] The first extractions with cooler water yield the highest quality gelatin with the mildest flavor, palest color, and strongest gel strength, and the quality decreases with later extractions in hot water.^[9] Each extraction is purified, concentrated, shaped, and dried. The batches are often blended by the manufacturer to get a consistent product with uniform characteristics.^[9] Type 'B' gelatin is made through a similar process but uses an alkaline solution rather than an acidic one to produce slightly different characteristics.^[3]^[10]

The majority of commercial gelatin is produced with pig skin.^[2]^[7]^[9] However, gelatin can also be produced to a lesser extent using cattle or fish skin and bones.^[2]^[10]^[9]

Characteristics

Gelling

The key characteristic of gelatin is its ability to form a clear, springy, elastic gel.^[5]^[9]^[10]^[11] When gelatin is hydrated and heated, it swells, melts, and dissolves into liquid.^[5] However, as a gelatin mixture is cooled, the gelatin protein strands tangle with each other to form a web that captures moisture and other components of the mixture.^[1]^[11] At low gelatin concentrations, this simply thickens the liquid, but at high concentrations the mixture solidifies.^[5] This solidification process is thermoreversible,^[2]^[4]^[12] which means that a gelatin gel can be heated to remelt it and then cooled to make a solid again.^[7]^[12] Because the web-forming process continues over time, these gels will continue to set and get stronger over time—gelatin products will be firmer in the days after production.^[2]^[9] However, eventually the gel will weaken again and weep liquids.^[13] Generally speaking, properly prepared gelatin can absorb 5–10 times its weight of cold water and, when melted and dissolved, set about 100 times its weight in water (depending on bloom strength; see below).^[3]^[7]

A few things can affect the gelling properties of gelatin. Most sugars will increase the gel strength by helping attract and sequester water in the mixture, and alcohol below about 30% of the mixture will strengthen it as well.^[2] Salt and acidity will both reduce its gelling strength.^[2]^[9] Certain fruits (papaya, pineapple, fig, kiwi, mango, and melon)^[2]^[7] also contain enzymes that break down gelatin and completely prevent it from setting;^[1] if you want to use gelatin with these fruits or their juices, you need to first heat the fruit to ≥185°F to destroy the responsible enzymes.^[2]^[7] Heat must be controlled when working with gelatin mixtures, since excessive heat denatures the gelatin and weakens it.^[9]^[12] Avoid boiling it or keeping it over 80°C/176°F for long periods of time.^[7]^[9]^[12]

Melted liquid gelatin sets around 59–68°F (15–20°C).^[2]^[14] When warmed, it melts completely by 80–90°F (27–32°C)^[3]^[9]—because this is below body temperature, gelatin-containing foods dissolve in the mouth and have a good texture.^[6]^[9]^[12] The exact temperatures depend on the gelatin's brand, bloom strength, and concentration.^[9] Fish gelatin is weaker and will both melt and set at much lower temperatures.^[2]

Forms

While always dried, unflavored food-grade gelatin typically comes in two forms: sheet (or leaf) and powder.^[1]^[7]^[11]^[14] Powdered gelatin is common in North America,^[6]^[15] where it can be found in bulk or in small packets of about ¼ oz / 7 g / 2¼ tsp.^[7] Sheet gelatin consists of dried gelatin shaped into translucent sheets, and it is more common in Europe.^[9] Importantly, sheet gelatin is standardized so that every sheet has the same gelling capacity, even across different bloom strengths (see below)^[7]—this means that a single high-bloom sheet will typically be lighter than a single low-bloom sheet.^[15] Whether to use powdered or sheet gelatin is a matter of debate.^[9] Some say that powdered gelatin hydrates more quickly and evenly and is easier to measure and adjust than sheet gelatin. Others say that sheet gelatin is easier to count, less messy, dissolves better, and contributes fewer bubbles.^[2]^[9]^[16] There is no objectively correct answer, and substitution guidelines are provided below.

Instant gelatin powder is a less-common option, formulated to require neither blooming nor heating to use.^[17]

Bloom strength

The strength of gelatin is measured as its "bloom strength", which reflects the firmness of its gel.^[7]^[12] This number, typically ranging from as weak as 50 to as strong as 300,^[6]^[10]^[12] is derived from the amount of weight needed to press a plunger into the gelatin once gelled.^[6]^[9] Higher bloom strength indicates a stronger, firmer gelatin (and vice versa),^[2]^[12] and you need less of it to gel a given quantity liquid in comparison to a lower-bloom gelatin.^[10] Additionally, because the gel strength is correlated to color and flavor, higher bloom gelatins will also be milder and paler, and they will set faster.^[9]^[15]

Gelatins of varying bloom ratings may be grouped into the following strength categories:^[2]

Bronze: 125–135
Silver: 160
Gold: 190–220
Platinum: 235–265

They may also be classified as low Bloom (<150), medium (150–200), or high (>220).^[10] Powdered gelatin in the United States is typically about 230–250 bloom unless specifically noted otherwise.^[9]^[12]^[15] Fish-derived gelatin is typically much weaker than that derived from pork or beef.^[6]^[10]

Selection and storage

The kind of gelatin you select will depend on a variety of factors, such as dietary restrictions, desired properties, and budget. For example, bovine gelatin is kosher and halal but less commonly available. Fish gelatin is kosher and halal, but it is weaker and can sometimes have a fishy odor.^[10] High-bloom gelatins are more expensive but often clearer and milder in flavor than low-bloom gelatins.

Store all dry gelatin in an airtight container away from light, heat, and moisture.

Techniques

Blooming

Before use, dehydrated gelatin must be hydrated or "bloomed" in cool water or other liquid.^[1]^[15]^[17] This allows it to evenly absorb water before melting and incorporation into your final product. If you were to stir regular dry gelatin into a hot liquid, it would gel without hydrating properly, causing lumps and strings in the mixture.^[2]^[12]^[16]^[18] The water must be cool to cold, and the gelatin must bloom for 5–10 minutes in order to properly and evenly swell.^[9]^[12]^[16]

Powdered gelatin is usually sprinkled over a set volume of liquid—usually 5–10 times the weight of the gelatin^[9]—which is generally specified by the recipe. Avoid dumping it in one clump, which can cause issues with hydration. Unlike powdered gelatin, sheet gelatin is usually fully submerged in an excess volume of the liquid, then removed and gently squeezed after blooming is complete.^[1]^[7]^[9] Because the sheet remains in one piece, there is no risk of it becoming diluted and lost in the large volume. You can also in theory bloom sheet gelatin using a fixed volume in the same way you would for powder.^[9]

Incorporation

After blooming, gelatin is ready for melting. If working with a sufficient volume of hot liquid (≥105°F/41°C),^[1] you can simply add the solid hydrated gelatin to the hot mixture and stir until fully melted and incorporated.^[9]^[15]^[16] Alternatively, the gelatin can be gently but fully melted over a double boiler or in the microwave—this is typically used when incorporating it into room temperature or cooler mixtures.^[1]^[9] Make sure it is fully melted, with no grains or lumps.^[7]

When working with cooler mixtures, it's important to bring the gelatin and the mixture as close together in temperature as possible to prevent textural issues. When the gelatin is too warm relative to the base, it can set up too quickly and cause lumps of congealed gelatin in the end product.^[1]^[9] One solution is to heat the gelatin well to ensure full melting, then cool it to a few degrees above the gelling temperature before incorporating into the mixture.^[7] You can also temper the mixtures—this is usually done by mixing a small portion of the cooler mixture into the warm gelatin and then mixing this back into the rest of the cooler mixture. For example, if you want to incorporate melted gelatin into whipped cream, stir some of the whipped cream into the warm gelatin, then fold this into the remaining whipped cream.^[9] Always make sure to quickly mix in the gelatin to ensure even distribution through the mixture before it sets.^[15]

Whipping

Much in the way that the protein in egg white allows it to be whipped to a stable foam, the same is true for the protein in gelatin.^[1]^[9]^[13] The whipping should be done just before the mixture is set, since it loses its elasticity and becomes brittle once set.^[11]

Molding

Because of their setting capacity, gelatin-containing mixtures are often molded while liquid and the allowed to set in the given shape before unmolding.^[7] To ensure clean unmolding, lining the mold with plastic or coating it with oil are important.^[13] Additionally, the molds should be prepared in advance, as the mixture may begin to set quickly after the gelatin is added.^[1]

Use

Gelatin is widely used in sweet and savory applications due to its nature as a thickener, stabilizer, foaming agent, gelling agent, and emulsifier.^[1]^[4] Depending on the strength and concentration used, it can add body to sauces or set a liquid enough to cut with a knife.^[1]^[15] The simplest application is for making fruit jellies—Jell-O is widely available and used for this purpose, but it can easily be made from scratch using unflavored gelatin. As a stabilizer, gelatin makes light dessert foams that hold their shape such as chiffon pies, bavarian cream, cold soufflés, and mousses.^[1]^[7]^[9] Similarly, it stabilizes the foam in marshmallows, but there it also lends a chewy and elastic bite, as it does in gummy candies.^[7]^[12] In ice cream and other frozen desserts, gelatin reduces the formation of ice crystals by binding to water,^[1]^[17] and it is used as a clarifying agent in juices and wine,^[3]^[10] where it binds to tannins and other impurities. Aesthetically, gelatin is also used to provide shiny surfaces, such as in clear and mirror glazes.^[13]

It's important to use the correct amount of the correct strength of gelatin. Not enough stabilizing power will weaken your gels, and too much will produce a rubber-like texture with an off flavor.^[1]^[7]^[16]

Substitution

In some situations, you may be unable or unwilling to use the specific gelatin (either form or bloom strength) called for by a recipe. In these cases, you need to know how to properly substitute equivalent types of gelatin.

When swapping different strengths of gelatin, you have multiple options. Since sheet gelatins of different strengths are often standardized to gel the same amount of liquid, you may be able to swap one strength for another, sheet-for-sheet.^[9] If you want to more precisely calculate by weight how much of a different gelatin strength to substitute, you can use one of the two following formulas—both are approximations:^[19]^[20]

$(mass_{gelatinA})(strength_{gelatinA})=(mass_{gelatinB})(strength_{gelatinB})$ $mass_{swapped}=mass_{recipe}{\sqrt {\frac {strength_{recipe}}{strength_{swapped}}}}$

Since recipes using powdered gelatin typically list a blooming volume while recipes using sheets do not, you need to take this into account when swapping.^[9] If swapping sheet for powder, make sure you're adding the full amount of liquid used to bloom for gelatin. For example, if a recipe says to bloom powder gelatin in 50 g of water but the sheet will only absorb a maximum of 40 g, you should add an additional 10 g water when melting the gelatin. If swapping powder for a sheet bloomed in a specific volume of liquid, use the same volume. If swapping powder for a sheet bloomed in an excess of liquid, bloom the powder in however much water the sheet would have absorbed.^[14] Five times the gelatin mass is a good starting point if you don't know or can't figure this out.^[15] No matter what, it's a good idea to make a test batch first.^[9]

If you want to use a gelling agent other than gelatin—such as for dietary restrictions—you will have to do some recipe testing to adapt the quantities and the method. For example, agar is stronger than gelatin by weight,^[7] and it melts/sets at a higher temperature. On average, agar is about 8 times stronger than gelatin, which means it takes 8 times less agar than gelatin to set a product to the same degree.^[21]^[22] Unlike gelatin, agar both sets and melts at a higher temperature—after dissolving in boiling liquid, agar sets at 95°F (35°C) and doesn't melt again until heated to 185°F (85°C).^[23]^[24] This makes it very stable, but it isn't as soft and melt-in-the-mouth, which can sometimes create a "crumbly" texture.^[22]^[25]^[26]