Learn the science behind:
Ever made your own stock, stored it in your fridge overnight and ended up with a jelly instead of liquid?
Ever made a wobbly sweet, soft panna cotta that only just sets in the fridge?
Or made a shiny, thin mirror glaze to cover your cake?
You might not realize it, but despite the fact that they taste and look so different, that stock jelly and panna cotta have one big similarity: gelatin. Gelatin is what transforms these two liquids into a gel, making it a ‘gelling agent’. But it can be a finicky one if you don’t use it right.
Where gelatin comes from
Gelatin is starts out as collagen which is one of the most common proteins in animals and fish (including humans). Beef, pork and fish are the most common materials used to make gelatin from their collagen. Skins and hides are particularly rich in collagen.
Collagen is made up of very large proteins, it doesn’t dissolve well in water and is very tough. Collagen is the so called ‘connective tissue’ in meats. Meats with a lot of collagen are tough. The only way to make them delicate and fall apart is by cooking them for long periods of time or under high pressure, as you do when making a stew or pulled pork for instance.
Collagen does not behave at all like the gelatin in your smooth, delicate panna cotta. But by cooking it down in those meat cuts it does become soft and tender. What has happened during cooking is that the collagen has transformed into gelatin! It’s also the reason why the stock surrounding the meat may turn solid, into a gel, when you cool it down. The gelatin that has formed causes this.
Transforming collagen into gelatin industrially
When you want to make large quantities of gelatin, you won’t use those high quality pieces of meat such as a shoulder to make the gelatin. Instead, you use the hides, skins, etc. to make the gelatin. In its essence the process is the same as you do when you make gelatin from your pulled pork, but it involves several additional steps to get all that collagen converted into gelatin efficiently.
The gelatin can’t be extracted from the animals that easily. The raw materials need to be pre-treated first to get a hold of pure collagen that can then be transformed into gelatin. During this pre-treatment fats, minerals and other undesired components are removed. The manufacturers also treat the raw materials with acids or alkali and enyzmes to help ‘loosen up’ the collagen. The collagen starts breaking down somewhat already and becomes easier to extract.
Once the materials have been pre-treated they are heated. During this well controlled process the collagen proteins break down further into smaller components. A manufacturer has to control all these processes well to ensure they make a gelatin with the desired properties. If the collagen breaks down too much it will form glue and if it doesn’t break down enough it will not form these flexible gels.
What is gelatin?
Collagen is a large complex protein. When you make gelatin, this protein is broken down into smaller pieces, called peptides. The protein is literally cut into pieces. By cutting the large protein into pieces its properties change significantly, it dissolves better in water for instance and it gets the ability to gel.
How does gelatin work?
The special thing about gelatin is that it can form very nice gels. These gels melt in the mouth and are pretty flexible and elastic. So how does gelatin forms those gels?
To make a gelatin gel you first have to dissolve the gelatin in warm water. Once you start cooling down the mixture the proteins will want to re-organize themselves. As a result they start forming structures, they will try rolling up again and interact amongst themselves. Three main types of interaction between the protein molecules make them hold their structure:
- Hydrogen bonds: these are bonds between OH-groups that point outwards of the proteins
- Hydrophobic interactions: parts of the protein that do not prefer to sit in water but in fat are called hydrophobic. In water they will try to lie together.
- Ionic interactins: parts of the proteins have a charge, this can be either positive or negative. Positive and negative attract and so stabilize each other.
All these interactions have an important thing in common: they are not permanent, instead, they are reversible. Whenever you heat up a gelatin gel these bonds will let go again and you end up with a liquid again!
Why does it form a gel?
So why do these interactions result in the formation of a gel? You make a gel when you’ve trapped the liquid inside. The liquid cannot move freely anymore and as a result the liquid transforms into something solid, a gel. This network of gelatin proteins is very good in holding onto those water molecules. They get trapped in between.
Other examples of a gel
There are a lot of other molecules that can form gels. Most of the gels though won’t be as elastic and smooth as gelatin. Good examples are pectin (part of jam), agar agar (a common vegetarian alternative to gelatin) as well as a lot of starches. All of them are large complex molecules which can structure themselves well in a liquid, entrapping the liquid molecules in between.
Different types of gelatin
As we mentioned earlier in this post, the way a gelatin is manufactured will impact its final performance. There are a few things you can watch out for.
Gelatin can be made from really any animal or fish part that contains a lot of collagen. However, in reality it is most commonly made from pig, beef or fish. Whether the gelatin is made from a young animal or an old one will influence how strong the final gelatin is. Also, fish gelatin in general makes for a weaker gel than the other two.
The more gelatin you use for making a gel, the stronger and firmer the gel becomes. But the strength does not just depend on the concentration. Some gelatins are simply stronger than others. Manufacturers have a way of indicating this through the so called bloom strength (g). The bloom value is measured by pressing down on a gel of the gelatin and determining the weight that can be put on the gel before it breaks. Manufacturers use a standardized test to determine this.
Sheet vs. powder
You will find gelatin in either powder or sheet format. Both types are gelatin and made in pretty much the same way, just the final steps will differ. Both can be used for the exact same applications. You will have to convert the quantities from one to the other, which can be a hassle. It is often best to just follow the instructions on the box since that will also take into account bloom strength (which is not always given on a pack!).
How to use gelatin
Since there are many different gelatins it is always wise to follow both as recipe as well as the instructions on the box to get the result you want. Luckily, there’s some standard steps you can always follow.
1. Hydrate gelatin
When you use gelatin you will notice that recipes will always tell you to soak the gelatin in room temperature, not warm, water. The gelatin you buy has been dried to make sure it stays good for a long period of time. Therefore, it needs some time to hydrate again, that is, to absorb the water. By soaking it in cold water first you ensure that everything hydrates before adding it to your product. Manufacturers of larger scale factories may add the gelatin directly into hot water, but they tend to have good mixers to ensure the particles are all broken up.
2. Don’t boil gelatin
Once you have added the gelatin to your product you should not heat it too much anymore. Gelatin and even though it can withstand quite warm temperatures, it will break down over time if you keep it at those temperatures for too long. As a result, the proteins become too small to form proper gels. Therefore, if you need to cook/boil your product do it before you add the gelatin.
Once you finished heating the other ingredients you can add the hydrated gelatin. It is no problem to add it to a warm mixture. Actually, it will help the gelatin dissolve quickly and fully since it will only start forming a gel below approx. 35C.
3. It takes time to firm up
Gelatin takes a while to form its gel structure. Most recipes will tell you wait a few hours. During this time the mixture might have to cool down and once cool the gelatin proteins need to organize themselves. Even after the gel is formed though it will continue to harden and firm up. If you leave your panna cotta in the fridge for a couple of days you will notice that it has hardened compared to the fresh one. Of course, it won’t harden indefinitely and after some time the hardening levels off.
4. Don’t freeze gelatin gels
Gelatin gels aren’t very resistent to low frozen temperatures. The ice crystals that form in the freezer can break the gel structures and as a result, some water will seep out when you thaw them again. It just isn’t as strong anymore. Best to just store your gelatin snack in the fridge.
Troubleshooting gelatin gels
Gelatin is a protein and for the gel to work it is important that the protein remains intact. As we discussed earlier, excessive heat can break down the gelatin and reduce the gel strength. But there is more that impacts gelatin gels.
Pineapple breaks down gelatin
Certain fruits (probably the most well known example is the pineapple) contain enzymes (proteases) which can break down proteins. Thus they can also break down gelatin, resulting in a weaker gel.
Enzymes can be deactivated by heat (enzymes are a type of protein as well). Therefore, you can use boiled pineapple, to make a pineapple jelly.
Impact of other ingredients
Besides completely breaking down gelatin, other ingredients can also just interfere with the protein strands that form a gel. Acids and salts tend to weaken the gel whereas milk and sugar strengthen it. If you know you’ll be using a lot of either of these you might want to adjust the amount of gelatin in the recipe to make up for it.
Not happy? Melt it and start over!
A gelatin gel is reversible. This means that you can melt the gelatin gel and form it nito another shape if you’re not happy with it. You can do this by simply warming up the gel. Again, don’t bring it to a boil, just heat it enough for it turn soft again and shape it.
Gelatin is a protein and excessive and repeated heat will slowly break down the proteins. As a result, you can’t do this revamping trick infinitely, after a while it will lose its strength.
Gelatin can be used in a lot of different dishes, both savoury and sweet. Any home made beef broth will contain gelatin. Marshmallow, panna cotta and a lot of candies (including Dutch liquorice) all contain gelatin. If you want to make an impressive shiny decoration for your cake, a mirror glaze, you will also need gelatin. You might also find gelatin in yogurts, though you don’t need gelatin to make a yogurt, yogurt can form a gel all by itself.
Madehow.com to learn more about the gelatin production process.
PBGelatins describe their production process in more detail with a nice compact overview.
This article is a little harder to get through but contains a lot of fact and figures and more in-depth information on gelatin.
Scientific article looking into the various sources of gelatin.
McKenzie for an explanation on bloom strength.
Harold McGee, On Food and Cooking, link
Fine cooking editors, The science of gelatin, from Fine Cooking #32, link
Simpson, B.K., Food biochemistry and food processing, 2012, chapter 21, link