Stories from the Lab: Gelatin Extraction in Action
In my last blog post, I shared how we experimented with agar, which is often used as a vegan substitute for gelatin. If you haven’t read it yet, it may be helpful to check it out before reading this one as we head back to the lab to find out just what gelatin is capable of! Think you know how gelatin is made and where it comes from? My classmates and I did an extensive lab experiment making gelatin from three different animals, and it led to some interesting findings.
What Exactly is Gelatin?
Gelatin is defined as a product obtained by the partial hydrolysis of collagen derived from the skin, white connective tissue, and bones of animals or animal byproducts. This collagen typically has high levels of cyclic amino acids, glycine, proline and hydroxyproline. Derived from a Greek word that means “glue producing,” collagen dissolves when heated in water and eventually turns into gelatin. It’s a large, extremely stable molecule that consists of a triple helical rod called tropocollagen.
Let’s talk science! The easiest way to transform collagen to gelatin is to denature soluble collagen. Hydrogen bonds and hydrophobic bonds help stabilize the collagen helix, which breaks the fibers and fibrils of the collagen. To extract this collagen from the animal’s connective tissue, it should be heated with water at 55°C. This allows the collagen to depolymerize and unwind. Gelatin molecules are very long and flexible that often gets tangled with one another. When heated, the structure of the collagen shrinks, which squeezes the juices from the muscle fibers.
Here are some interesting facts about gelatin you may not know:
- Most animals have a larger supply of collagen when they are younger than when they’re older, due to the movement and working of its muscles. The collagen becomes more insoluble and the stronger muscle fibers are crosslinked.
- Gelatin for food purposes has been around since 1685 in Holland.
- The most commonly used form of gelatin in America and Europe is pig skin, which tends to be the most popular animal protein option since it takes the least amount of time to extract and manufacture.
- Gelatin is sold in several forms. Some of these forms are purified gelatin, which includes leaf, cold soluble, and powdered; sheet gelatin; and granulated gelatin.
Time for Some Serious Gelatin Extraction
In my Ingredient Functionality class, gelatin extraction was the focus and purpose of our lab experiment. With the help of Dean Ted Russin and Chef JJ Lui, we analyzed three different animal proteins—cod fish, pork feet, and chicken wings—for differences in melting weights at different temperatures, specifically 25°C, 37.5°C, and 45°C.
It took a number of steps to extract the gelatin:
- 225 grams of each protein was combined with 225 grams of water in vacuum-sealable bags and cryovaced.
- These bags were added to circulating water baths at 90°C for two hours.
- The proteins were then removed and the liquid was strained.
- 40 grams of each protein liquid was measured and added to 4 falcon test tubes, with 10 grams of liquid in each.
- Each protein liquid-filled falcon tube was then transferred to each water bath, so that there were three different falcon tubes in each thermocirculator for 10 minutes.
- After the 10 minutes, the samples were taken out of the thermocirculators and weighed.
Protein liquid in falcon test tubes Protein liquid-filled falcon tube transferred to water bath
The results were interesting. At 25°C, the fish had the highest weight, followed by chicken and then pork. At 37.5°C, the chicken had the highest weight, followed by fish with pork again coming in third. The 45°C yielded the same results as the lowest temp—fish had the highest weight, then chicken and pork in that order. The closest similarities in weight were between fish and pork at 37.5°C, with a 0.07 difference between the two samples. The biggest difference in weights was at 25°C between Fish and Pork, with a 0.95 difference.
Fish was rated to have the strongest flavor, followed by pork and then chicken. The appearance of the stocks varied with each protein as well. Pork was light brown, chicken was cloudy white, and fish was an off-white, clear color. The aromas were as expected—the fish had a pungent, seafood, fishy smell; while the chicken and pork had a meaty smell.
The Many Faces of Gelatin
Why is it important to be so familiar with the properties of gelatin? In the culinary industry, gelatin is used for several different applications, including marshmallows, gummies, and candies. Chefs tend to use gelatin for foaming formations, water binding, emulsification, and viscosities. Soups, sauces, and stocks are often thickened with gelatin. It can be used as an emulsifier for whipped cream and as a fining agent to clarify wine or fruit juices. Gelatin is also useful as binding agents in meat rolls and dairy products, as an emulsifier in sauces and cream soups, and a thickener in jellies and puddings.
Gelatin has more uses than most people think. Who knew? So now, instead of buying gelatin, you can make it right at home with any leftover meat items that you have.
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