1. Why Raw Pineapple and Kiwi Fruit Stop Gelatin from Setting
According to gelatin manufacturers, raw pineapple and kiwi fruit contain enzymes that break down gelatin, preventing the jelly from setting. [6] The solution is to cook the fruit first or use canned fruit. Since canned fruit has already been heated, the enzymes are no longer active. [6] This clue—that heat stops the enzymes from preventing gelatin from setting—helps us understand the science behind it.
However, if you use agar instead of gelatin, the jelly will set even with raw pineapple. [3] Since both are used to "set" foods, why does one fail and the other succeed? The answer lies in what they are made from. [3]
The reason agar is not affected by pineapple has to do with what it is made from. Let’s look at that next.
2. How Gelatin from Animal Collagen Differs from Agar from Seaweed
Gelatin is made from collagen, which is found in the bones and skin of livestock like cows and pigs. It is heated to loosen the structure and turned into a protein that dissolves easily in water. [1] Making glue from animal parts is said to date back to ancient Egypt, but edible gelatin as we know it is thought to have been developed in the 1800s. [1]
Agar (called kanten in Japanese), comes from red algae such as tengusa and ogonori. Its main component is a chain of two types of sugars. It is not a protein; it is a type of dietary fiber. [2] The National Diet Library in Japan also explains that gelatin is a protein, while agar is a type of carbohydrate. [3]
This difference explains the pineapple puzzle. Pineapple contains an enzyme called bromelain, which breaks down proteins. Because gelatin is a protein, it loses its stickiness and fails to set. Agar is not a protein, so it is not affected by the enzyme. [3]
Agar does have its own weakness. If it is heated for a long time in an acidic state, the network that holds it together can break, making it hard to set. To avoid this, sour fruit juices should be added after the agar has been taken off the heat and cooled slightly. [3]
3. Why Gelatin Melts in Your Mouth While Agar Stays Firm in Summer
The most important feature of gelatin is that it can be heated to melt and cooled to set, over and over again. [1] One source states that gelatin sets at about 5 to 15°C (41 to 59°F) and the finished jelly begins to melt at about 20 to 30°C (68 to 86°F). [4] Because different sources give slightly different numbers, these are rough estimates.
The temperature inside your mouth is about 37°C (98.6°F). Since gelatin melts at a temperature lower than this, the jelly breaks down smoothly when you eat it. [4] This is also why gelatin jelly can melt if left in a hot room in summer. [5]
Agar behaves differently. It sets at about 40°C (104°F) but does not melt until about 90°C (194°F). Some types do not melt even at 100°C (212°F). [2] The melting temperature is listed as starting in the 80°C range (176°F) in some sources. [4] Once dissolved, agar will set at room temperature without needing a refrigerator. [2]
Because there is such a large gap between the temperature where agar sets and the temperature where it melts, it keeps its shape even at summer room temperatures. [4] Whether a jelly melts in your mouth depends on where these temperature points fall.
When reading about gelatin, be careful to distinguish between two different temperatures: the temperature needed to dissolve the powder (about 40 to 50°C or 104 to 122°F) and the temperature where the finished jelly starts to melt (about 20 to 30°C or 68 to 86°F). [5] Checking which temperature a source refers to prevents confusion.
4. How Agar Was Discovered from Forgotten Tokoroten in Kyoto
There is a popular story about the origin of agar. It is said that around 1658, an innkeeper named Minoya Tarozaemon in Fushimi, Kyoto, forgot some tokoroten (a jelly made from seaweed) outside. [7] The jelly froze in the cold night air and melted in the daytime sun, repeatedly losing its water content until it looked like dried food. According to the story, when this dried substance was dissolved in boiling water and cooled, it became a clear, odorless jelly. [7]
This story is a tradition passed down by companies, and the discoverer and exact year are not confirmed facts. [7] A reliable record is found in the encyclopedia Wakan Sansai Zue, compiled in the early 18th century, which states that agar was made in the village of Fushimi. The City of Kyoto notes that agar was mainly produced in Fushimi during the early Edo period. [8]
There is also a legend that the name "agar" was given by the Obaku Zen master Ingen. However, this is also not a confirmed fact. [8]
Agar has uses beyond food. It has been listed as a crude drug in the Japanese Pharmacopoeia since 1920 (Taisho 9). [2]
The story that Ingen Zenji gave agar its name is also a tradition, with limited evidence. [8]
5. How to Check Whether Your Jellies Use Gelatin or Agar at Home
You can investigate this yourself at home. Look at the ingredient labels on jellies or yokan (a sweet bean jelly) you have in your kitchen. Check if they use gelatin or agar. If you have both, taste them side by side. Notice how gelatin melts smoothly in your mouth while agar has a firmer texture and holds its shape. No fire or knives are needed for this observation. [2]
For more information, you can read "What is Agar?" and "History of Agar" by Ina Food Industry, or "What is Gelatin?" by the Japan Gelatin and Collagen Manufacturers Association. These resources are available in Japanese. For a comparison between legend and record in the history of agar, the Kyoto City tourism website’s page on the "Birthplace of Agar" is also worth checking. [8]