mandarin panna cotta in glass

The Science of a Wobbly Panna Cotta (+ Mandarin Panna Cotta Recipe)

There aren’t a lot of desserts that require quite minimum effort and still look highly sophisticated. Panna cotta though is one of the few desserts that does fall into that category. Made with as little as three ingredients (cream, sugar, and gelatin) and requiring more patience than anything else, it’s a great quick dessert that looks and tastes sophisticated.

If you’re a fan of Masterchef Australia you will have seen a lot of panna cotta come by. It’s a favorite dessert of contestants when strained for time and still needing to make something exquisite. It can be a lifesaver, but a downfall as well. Just a little too short on time for that panna cotta to set, instead ending up with a liquid is a small disaster. Making a panna cotta that’s too firm isn’t appreciated either. Instead, what you’re looking for, is that perfect wobble.

Despite the simplicity, achieving that perfect wobble isn’t always easy. There are a lot of ways to mess up a panna cotta and we’ll try to discuss most of them here!

What is a panna cotta?

A panna cotta is a wobbly, generally sweet, gel that can be made with just three ingredients: cream, some sugar and gelatin. It essentially is a sweetened and gelled cream dessert. You will find panna cotta on a lot of restaurant menus, since it’s perfect to prepare in advance.

Panna cotta is very versatile and there are plenty of possible variations. You can add all sorts of flavors to a panna cotta, such as spices and fruits. Also, instead of just using cream, you can add various types of milk or fruit purees to mix things up.

If you look more closely at a panna cotta, at a molecular level, you will notice that the cream is interspersed by a lot of gelatin molecules. These gelatin molecules form a network that prevents the cream from moving around freely. The sugar is dissolved and spread throughout, holding onto some water. It’s quite a delicate texture.

Panna cotta making challenges

Making a panna cotta is deceptively simple. You heat up your cream and sugar, to ensure that all the sugar molecules dissolve. Next, you add gelatin and you let it set. Despite the simplicity, making a panna cotta can go wrong quite easily, especially if you start adding other ingredients, or chaging things up a bit!

There are three main challenges you may run into when making a panna cotta:

  • The texture, you want to create a panna cotta structure that isn’t liquid, but that hasn’t firmed up so much that it doesn’t wobble anymore either. The ideal panna cotta for most is one that is just enough set to hold its shape. It should ‘wobble’ on a plate. Using and dosing your gelatin just right is key here.
  • The panna cotta should taste good and have interesting flavors, but, in such a way that you do not prevent the gelatin from doing its job. You want to balance the fat from the cream with the other (possibly) lighter ingredients.
  • Lastly, you don’t want your panna cotta to split into separate layers while it’s setting. Even if both layers set well.

Impact of ingredients on the wobble

The most important and most crucial step of making a panna cotta is to make that perfect gel texture. Gelatin is great at this. It can form gels that melt in the mouth and give a very smooth luxurious eating experience.

Unfortunately, using gelatin is not always straightforward. Almost all ingredients in your panna cotta impact just how the gelatin gels in your panna cotta. Slightly tweaking your recipe may impact the gel more than you might expect.

4 different panna cotta recipes
Testing the impact of water, lemon juice and kiwi on the panna cotta texture. Here the mix is still liquid.

Type of gelatin

Whether the final panna cotta gel wobbles depends on how well the gelatin was able to do its job. If you use too much, it becomes too firm, too little and you’ll end up with a puddle of ingredients on a plate. Getting the concentration of gelatin just right is essential.

When choosing and using gelatin, keep in mind that gelatin from different manufacturers can behave very differently. Manufacturers may have slightly different processes to make their gelatin for instance. Also, they may use other raw materials to make their gelatin. Gelatin can be made from pigs, cows as well as fish and manufacturers don’t always clearly mention the origin of their gelatin.

Another parameter to keep in mind is the strength of gelatin, which can be expressed in “bloom”. A higher bloom value refers to a stronger gelatin which will result in a firmer panna cotta. Industrial gelatins will clearly mention this whereas consumer gelatins often do not.

If you’ve figured out a good concentration of gelatin for your panna cotta, it is smart to stick with that same brand going forward. If you do want to change, do a test batch with your new gelatin to double-check whether it behaves the same!

Impact of sugar

Once you’ve chosen your gelatin, it’s time to look at the impact of other ingredients on your gel. Gelatin gels your panna cotta by forming a network of all the different gelatin molecules in which the liquids are ‘captured. Ingredients that interfere with this network can impact the texture of your panna cotta.

It is likely that your panna cotta recipe contains sugar (sucrose). Sugar gives sweetness to your panna cotta but it also impacts the strength of the gel of gelatin. The impact of sugar depends on the type of gelatin, but reducing the sugar content may decrease the firmness of your panna cotta. Replacing sucrose (regular sugar) with other sugar syrup or sugar types will, of course, impact flavor, but may also impact texture, something to test for when you’re trying out a new variation!

Impact of acidity

Gelatin is a protein. Proteins tend to be impacted by their environment, influencing their 3D structure and functionality. In the case of some gelatin types (mostly porc based) the pH-value, which is a measure for acidity, is known to interfer with the gelling properties of gelatin. Making the panna cotta too sour, for instance by using lime or lemon juice, can prevent the network formation of gelatin. As a result, your panna cotta won’t set as nicely as you had hoped it would.

Other gelatins may be less sensitive to this phenomenon. If you have trouble with your panna cotta not setting and you’re using these acidic ingredients, test it with less or none of it to see if that fixes the problem!

Enzymes break down gelatin

Certain specialized enzymes in food can break down gelatin protein molecules. The enzymes, called proteases, cut the protein into smaller pieces. Those smaller pieces can’t form the entangled network that is required to gel the panna cotta. As a result, your panna cotta won’t set.

Several fresh fruits such as kiwis, papayas and pineapples contain these enzymes. If you blend these into your panna cotta your panna cotta will never set. The enzymes break the gelatin down before it has a chance to firm up the panna cotta.

If you want to use an ingredient that contains these enzymes you have to deactivate the enzymes. You can deactivate them by cooking them for a short period of time. It is why canned pineapple doesn’t give you any trouble. The heat treatment that the canned pineapple has undergone is sufficient to deactivate the enzyme!

In the photo below you can see that the panna cotta made with cream is well set. Where part of the cream (a little over 10%) was replaced by water or lemon juice, the panna cotta has still set well. However, added some crushed kiwi left the mix completely liquid! It hadn’t set at all.

4 different panna cotta recipes, set

Impact of process on your wobble

To complicate matters, gelatin needs time to set. You will only know whether you used the right amount of gelatin when you put your spoon into your panna cotta upon eating. And during this time that the gelatin needs to do its work, you need to treat the panna cotta well to achieve your perfect result.

The impact of time

A panna cotta needs time to set. During this time the temperature of the panna cotta cools down and the gelatin molecules reorganize themselves to form a network. Only when the temperature is low enough will that network really be formed. The texture of the panna cotta changes quite rapidly in the first two hours of cooling. If you check too soon the gel may not have been formed.

Unfortunately, there’s also such a thing as checking too late. A gelatin gel never really stops firming up during storage. Even though it firms up a lot more slowly after the first few hours, the gelatin molecules will continue to slowly rearrange themselves even more optimally. It is why your leftover panna cotta may be so much firmer than the fresh panna cotta you ate the day before. Especially if you’re only given it a short time to set, the difference will be noticeable.

The impact of (too much) heat

Gelatin does not dissolve well at low temperatures. It is why you always have to heat up the liquid you want to set for your panna cotta. In a warm mixture the gelatin dissolves very rapidly. Take care though, there is a very good reason recipes only ask you to add the gelatin at the end of the cooking process. The gelatin proteins, like most proteins, don’t handle high temperatures for long periods of time very well. If you boil your gelatin mixture for a couple of minutes a lot of that gelatin will break down and your panna cotta will never firm up well anymore.

The impact of (too much) cold

Yes, gelatin needs cooler temperatures for it to form that desirable wobbly panna cotta textures. Unfortunately, there’s also such as thing as too cold. Whereas you can set your panna cotta in the freezer in case of an emergency, the quick frozen panna cotta won’t be as stable as a more slowly set panna cotta.

While a panna cotta is setting the gelatin molecules are constantly reorganizing themselves more efficiently. If they are frozen though they can’t make these smaller adjustments and will be locked in place more quickly. The panna cotta will set (Masterchef Australi has plenty of evidence for this) but it will be different. If you then store the panna cotta in the fridge though, it will slowly reorganize again and regain some of that strength.

4 blueberry panna cotta tests
Blueberry panna cottas

Preventing a split panna cotta

Even if you’ve done everything perfectly, chosen the right recipe, followed the correct steps for setting the gelatin, you could end up with a great strength of a panna cotta, but one that has split into two layers!

Chances of this happening seem to be the largest when you use a mix of milk and cream. Cream contains a large amount of fat whereas milk only contains a few percent. When the mixture is cooling down it is possible that the fat floats to the top due to the difference in density of fat and water (that process is called sedimentation). This process can only take place when the molecules can move around easily. As long as the mixture is warm that is the case. However, once the mix cools down the mobility of molecules in general decreases. Also, the gelatin will start to thicken the mixture. If you whisk the mixture through one more time at this point before portioning the panna cotta the molecules shouldn’t be able to move as much anymore, preventing the splitting!

Fruit skins floating to the top

Have another look at those blueberry panna cottas above. The two samples on the left side were poured into their glasses when still warm. However, the two on the right were cooled down some more, before being stirred again and poured in the glasses.

Notice how the two left samples have skins of blueberry floating at the top (see also photo below)? Whereas the other two have the skins mixed more throughout, thus being less visible?

By waiting a little longer to pour the gelatin has started to thicken the mixture slightly. By stirring it through one last time at this point your prevent the skins from being able to float up. The viscosity of the panna cotta is already too high for sedimentation to occur!

4 blueberry panna cotta tests

An aerated panna cotta?

A close relative of the panna cotta is what we Dutch call a ‘bavarois’. The English name seems to vary (it is not a Bavarian cream, which is made with eggs). However, whereas the base of a panna cotta is the cream, with the possible addition of some fruit, it is the other way around for a bavarois. A bavarois has a fruit puree as its base and adds cream once the fruit has cooled down.

Because you’re adding the cream cold you can actually whip the cream to create a delicious airy structure! Cream can’t be whipped anymore once you’ve brought it to the boil which makes it a no-go for a regular panna cotta. Thanks to the aeration, you end up with a mousse like texture!

aerated raspberry bavarois on spoon
Raspberry bavarois
mandarin panna cotta in glass

Mandarin panna cotta

Yield: 4 portions
Prep Time: 1 hour
Cook Time: 30 minutes
Total Time: 1 hour 30 minutes

A simple dessert that requires more patience, than actual work. It has a slight hint of mandarin and works great with chocolate or roasted almonds.

Ingredients

  • 110g cream
  • 50g milk (you can use non-cow's milk, e.g. coconut milk)
  • 25g sugar
  • 1 large or 2 small mandarins*
  • 1,5 sheet or 3g of powdered gelatin (see notes)
  • few drops of vanilla extract (optional)
  • water

Instructions

  1. Start by flavoring the cream. Zest the mandarin(s). Add the zest and the juice of the mandarins(s) to your cream. Add the sugar.
  2. Bring the cream to the boil stir to help dissolve the sugar. Turn off the heat, cover with a lid and leave on the stove top for 30-60 minutes. During this time the flavour from the mandarin will infuse into the cream. If you're in a rush, you can shorten this time to just a few minutes, but it will be less strong in flavour.
  3. Prepare the gelatin. If using sheet gelatin add it to a bowl of plenty of cold water for approx. 10 minutes. After ten minutes the gelatin should have softened completely. Take the gelatin out of the water and squeeze off any excess water. If using powdered gelatin, you have two options. Either add the powder to the cold milk and mix it through. It will thicken the milk considerably. Or, dissolve the powder in water according to the packs instructions (a 7g pack tends to require 60g of water). Wait a few minutes to allow the gelatin to fully soak before proceeding.
  4. Re-heat the cream mixture and bring it to the boil. Once it's boiling, take it from the heat and whisk in the gelatin. Because of the heat, the well-soaked gelatin should dissolve immediately.
  5. Optionally, add the vanilla extract.
  6. Pour the panna cotta mixture in glasses or silicon molds (for easy release). Leave to set in the fridge for at least an hour.
  7. If you need to eat soon, add a little more gelatin, if you want to leave them in the fridge for a couple of hours, add a little less!
  8. Enjoy, either within the glass, or unmold it onto a plate.

Notes

Gelatin: the quantity depends a lot on the type you use and this can differ quite a bit between countries. Here are a few guides, but it might be that your panna cotta turns out too soft or firm. In the case of the former, add more gelatin next time, in case of the later reduce the gelatin content. A note on the quantities mentioned in the recipe:

  • The sheet is a regular strength sheet from Dr. Oetker made from porc, one sheet weighs about 2.5g
  • The powder is also of regular strength, often this is packed in packets of 7g. If you don't have such an accurate scale. Dissolve the 7g in 60g of water (or according to the instructions of the packet) and add 25g of the gel that has formed.

*You can use other flavours for panna cotta, it is what makes it so versatile! Consider steeping some spices (e.g. a cinnamon stick, cardamom seeds, a scraped open vanilla pod) or use another citrus fruit. Just don't make it too acidic or you might curdle the milk!

If you gave it a try, let us know!

A note on the experiments

This post contains various photos of experiments on panna cotta. These experiments were done as follows.

Kiwi vs Lemon juice vs Cream vs Water

This experiment was done with the mandarin panna cotta recipe, however, without the addition of mandarin to save time and ingredients. A core base components was made by gently heating 125g of cream with 60g of sugar. 2,5g of powder gelatin soaked in 22,5g of water was mixed in the warm mixture and left to room to just above room temperature. The samples all contain 15g of their added ingredient: cream, water, lemon juice or kiwi. The samples were left to set in the fridge for >4 hours.

References

Chest of books, Gelation And Stiffening Power Of Gelatin. Continued, link

S.-S. Choi, J.M. Regenstein, Physicochemical and SensoryCharacteristics of Fish Gelatin, JOURNAL OF FOOD SCIENCE—Vol. 65, No. 2, 2000, link

Harold McGee, On Food and Cooking, Scribner, 2004, p. 606-609

Fernando A. Osorio, Elizabeth Bilbao, Rubén Bustos & Fresia Alvarez (2007) Effects of Concentration, Bloom Degree, and pH on Gelatin Melting and Gelling Temperatures Using Small Amplitude Oscillatory Rheology, International Journal of Food Properties, 10:4, 841-851, DOI: 10.1080/10942910601128895

Parks, S., 6 Unexpected Factors That Can Ruin Your Gelatin Desserts, June-7, 2016, link

Zandi, Mojgan & Mayer, Christian. (2007). Effects of Concentration, Temperature, and pH on Chain Mobility of Gelatin during Early Stages of Gelation. Iranian Polymer Journal. 16. 861-870, link

Handbook of Food Proteins. United Kingdom: Elsevier Science, 2011.

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2 comments

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  • Very interesting, we love pannacotta here at home.
    As a professor at a biology institute teaching interdisciplinarity in science I shall certainly use this paper.

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