Jello is a popular gelatin dessert that is made by dissolving gelatin in hot water and then allowing it to cool and solidify. Unlike many other desserts, jello retains its soft, wiggly texture even when fully set. This has led many people to wonder – why doesn’t jello harden?
What is Jello Made Of?
The key ingredient in jello is gelatin. Gelatin is a protein derived from collagen in animal bones and skin. It has unique properties that allow it to form thermoreversible gels. This means that gelatin can transition between liquid and semi-solid states depending on temperature.
At high temperatures, gelatin will dissolve in water. As it cools down and reaches its setting point (which varies based on gelatin bloom strength and concentration), the gelatin proteins begin to bond and form a mesh-like molecular structure that gives jello its characteristic soft solid texture.
Unlike materials that form permanent chemical bonds when they set, gelatin’s bonds are physical in nature. This means they can break and reform repeatedly with changes in temperature. As a result, jello never fully hardens.
Factors That Influence Jello Texture
While gelatin is essential for making jello, other ingredients and conditions impact the final texture:
Gelatin Bloom Strength
Gelatin is available in different bloom strengths, which refers to how much weight gelatin can support as it sets. Higher bloom strengths like 250-280 form firmer, resilient gels while lower blooms around 150-190 produce more delicate, fragile gels. Jello typically uses mid-range bloom strengths around 220 for its signature soft, spoonable texture.
Gelatin Concentration
The more gelatin used, the stiffer the jello will set. Jello brand gelatin contains gelatin at a concentration that provides enough structure to allow jello to hold its shape while remaining soft and jiggly.dou
Ingredients
Adding chunky ingredients like fruit and whipped cream makes jello softer than jello with just water or juice. The solid pieces disrupt the protein network, preventing it from fully gelling.
Setting Conditions
Setting jello in the refrigerator rather than at room temperature allows a looser protein network to form, creating a softer gel. Allowing jello to fully set overnight results in the firmest possible texture.
Why Doesn’t Jello Harden?
With this understanding of its ingredients and setting process, we can answer the original question – why doesn’t jello harden?
Gelatin Forms Physical Bonds
Unlike gels made from alginate or pectin that form permanent, irreversible chemical crosslinks, gelatin only forms temporary physical bonds. These reversible bonds between gelatin proteins continuously break and reform at room temperature. This keeps the gel network dynamic and unable to truly harden.
Hydrogen Bonding
The physical bonds that hold jello together are hydrogen bonds. Hydrogen bonds are very weak compared to covalent bonds and are easily broken by thermal energy at room temperature. The movement of the gelatin mesh is what gives jello its distinctive wobble.
Thermoreversibility
As described earlier, gelatin can transition between liquid and semi-solid states based on temperature. At high enough temperatures, the weak hydrogen bonds are disrupted, turning solid jello back into free-flowing liquid. This thermoreversible nature of gelatin gels prevents permanent hardening.
Trapped Water
Jello’s soft gel network traps a large amount of water within the structure. This hydration allows jello to retain its flexibility and also contributes to its melting texture. As the gelatin chains move, they redistribute the water molecules they have trapped.
When Does Jello Harden?
While jello doesn’t ever fully harden, there are some situations where it can become firmer and more solid:
Prolonged Refrigeration
Given enough time setting up in the fridge such as overnight or longer, jello will reach its maximum firmness as the gelatin networks have ample time to fully form. However, it will soften again after about an hour at room temperature.
High Bloom Gelatin
Using gelatin with a bloom value over 250 results in a thicker, more cohesive gel network that gives jello a firmer texture. Professional recipes designed to produce jello shots to hold their shape often use very high bloom gelatin for this reason.
High Gelatin Concentration
Increasing the amount of gelatin powder per volume of liquid makes jello more solid. Specialty jello products designed to maintain their form like jello jelly candles use up to triple the normal amount of gelatin.
Addition of Thickeners
Mixing in starches like corn starch or gums like locust bean gum binds additional water and reinforces the gelatin matrix, producing firmer jello. However, too much thickener can make jello rubbery.
Salting Out
Adding a small amount of salt to jello can cause the gelatin proteins to aggregate or “salt out”, forming a tighter network and firmer gel. This effect can be enhanced by also adding acid like lemon juice.
Conclusion
Jello’s soft, wobbly texture results from its thermoreversible gelatin matrix. The weak physical bonds holding the gel network together easily break and reform at room temperature, preventing jello from ever fully hardening like a permanent gel. While jello can be firmed up by chilling, using high blooms, increasing gelatin concentration or adding thickeners, its signature squishy, melting texture comes from gelatin’s thermal reversibility.
So the next time you enjoy a perfect spoonful of wiggly jello, you’ll know the science behind why it jiggles!