Color changing ice cream is not new at all. There is a patent here which was filed in 2001 for a "Frozen dessert novelty which changes color". It describes the use of "red cabbage extract (anthocyanin)" to achieve the effect.

In 2014 a Spanish Man named Manuel Linares went viral with his claim that he had invented a color changing ice cream. If you search the term you will find a many newsletter articles. The formula was claimed to be a "patent-pending secret" which changes color in response to temperature changes and acids found in the human mouth. You can find a video of it here, where you can see him spritzing a liquid onto it (he called it "love elixir" which causes the ice cream to change from blue to red. After seeing the video I immediately knew what was going on and wanted to write an Instructable about it, but got side tracked somehow. I knew that the effect was not due to the acids in the human mouth (the normal pH range for saliva is 6.2 to 7.6, so it is actually quite neutral *), but because the liquid he used was some type of acid i.e. lemon juice and the ice cream itself had a neutral pH value. Low and behold the patent (here) proved what I thought and is basically the same as the one above.

I still think it is a fun idea and decided to play around with it.

*) pH is a scale used to specify how acidic or basic a water-based solution is. Acidic solutions have a lower pH, while basic solutions have a higher pH.

Step 1: Where to Get the Colour Changing Pigments - Anthocyanins

As described in the intro step the "magic" behind the color change are water-soluble pigments called Anthocyanins.
The name stems from Greek: ἄνθος (anthos) "flower" and κυάνεος/κυανοῦς kyaneos/kyanous "dark blue". They are found mostly in flowers and fruits, but also in leaves, stems, and roots. They are red or pink in acidic solutions, purple in neutral solutions, greenish-yellow in alkaline solutions, and colorless in very alkaline solutions, where the pigment is completely reduced [1].

As you can see in the image underneath the chemical structure and therefore the color changes with the pH value.

CC BY-SA 3.0 (the original image can be found here, remixed by me)

So the first thing I had to figure out is to where to get the anthonyanins from.

In his patent Manuel Linares describes the extraction of the pigment in the following way:

"1.5 kg of cabbage and 15 liters of water. The water is heated to a temperature between 60-70 °C and reserves. In this example, the water is heated to a temperature of 62 °C.
Cabbage triturated in diminutive sizes. Then, water is added to the shredded cabbage and continue grinding with a blender or similar apparatus for 5 to 10 minutes. This mixture of shredded cabbage and water is allowed to stand.
The mixture is then filtered and the filtrate is sent to cool in cooling to a temperature of 10 ° C for subsequent freezing at a temperature between -16 and -24 ° C. This filtrate is the liquid plant extract is incorporated in food products of the invention."

There is also an instructable that uses cabbage to make a Color-Changing Martini.

Luckily there is an easier way to get it. Blue flowers are a common ingredient in teas and therefore easily available. Two very common ones are Butterfly Pea Flower Blossoms and Blue Mallow Flowers. There is another instructable that uses Butterfly Pea Flower Blossoms to make Color-Changing Cocktails.

Even easier than using the flowers is using pure blue matcha powder which can luckily be bought relatively easy online. So for for the ice cream I decided to go with blue matcha powder made from Butterfly Pea Flower Blossoms.

If you are interested in learning further about anthycyanins I suggest reading this article.

Step 2: What to Use As Ingredients

So the next thing that I had to figure out was which type of ice cream base to use. The first thing I did was to do some research.

In the table underneath you can see the pH values of different liquids.

Liquid	pH value	source
Egg white	7.6 (fresh) to 9.2 (old)	[2]
Water	7
Milk	6.5 to 6.8	[3]
Cream	6.5 to 6.8	[3]
Coconut milk	6.1 to 7.0	[4]
Buttermilk	4.4 to 4.8	[4]
Yogurt	3.0	[3]

So in terms of using a base that is as alkaline as possible you should go with old egg white (please don't!!). Milk, coconut milk and heavy cream all have about the same pH value, while buttermilk and yogurt are more acidic.

I tried finding an ice cream recipe using egg whites and couldn't find one I liked (If you have one please share it with me, I would love to try it.). So I decided to go with milk, cream and coconut milk for my colored ice cream and yogurt for the acidic counterpart.

I noticed that heating up whatever base I used is really important in order to extract and intensify the color of it.

As you can see in the first picture, coloring coconut milk somehow works better than milk or heavy cream (I have used the same amount of matcha powder for every liquid). This also translates to the final ice cream. As you can see in the second picture the coconut ice cream (on the right) looks bluer than the dairy one (on the left). The color changing effect also works better with coconut ice cream, so I suggest you go with.

[2] Brown A. (2011). Understanding Food: Principles and Preparation, Fifth Edition, Cengage Learning, Stamford, Connecticut, USA

Step 3: Version One: Coconut Ice Cream - Step 1

Ingredients:

3 cups of coconut milk
1/3 cup of sugar
1 tsp vanilla extract
2 tsp Blue Pea powder (e.g. here (affiliate link))
pinch of salt

Preparation

Making the ice cream is very simple. Simply add all the ingredients to a pod, stir them and heat them up as shown in the next step.

If you want to store your ice cream in a freezer, you might want to consider replacing the sugar with the same amount of corn syrup. This way the ice cream will be smoother and easier to serve once you take it back out. Here is a great article about ice cream science and the effect of different ingredients should you be interested.

Step 4: Version One: Coconut Ice Cream - Step 2

Once you have combined all the ingredients you will have to heat them. The reason for this can easily be seen in the pictures. Extracting the color from the Blue Pea powder works way better if you heat the mixture. There is some scientific research should you be interested here.

Just heat the mixture slowly until it doesn't turn any bluer. Make sure to stir the whole time to prevent it from boiling over. If you are not happy with the saturation you can add more Blue Pea powder. Remember that once the ice cream is frozen, the color will look less intense.

Once the mixture has a nice and even saturated blue tone, fill it into your ice cream maker and let it cool down. Don't leave it out to long without stirring or it will form a skin, which depending on how well your ice cream maker stirs won't leave you with an nice and even result.

Step 5: Version Two: Vanilla Ice Cream - Step 1

Most vanilla ice cream recipes I know use egg yolks. I decided against using them, since I wanted the base ingredients to be as white as possible. So here is the recipe I used:

Ingredients:
2 cups of heavy cream
1 cup of milk
3/4 cup of sugar
1 tsp vanilla extract
2 tsp Blue Pea powder (e.g. here (affiliate link))
pinch of salt

Preparation

As with the coconut ice cream the preparation is really easy. All you need to do is to combine all the ingredients in a pot, mix them and heat them up while constantly stirring. As you can see in the picture heating up the mixture is really fun to do since it will get bluer and bluer. Once it doesn't get any more saturated, fill the mixture into your ice maker and let it cool down.

Again remember that once the ice cream is frozen, the colour will look less intense. So make sure that after cooking it has a nice saturated tone. Depending on the concentration of the powder you might want to add more.

Step 6: How to Serve It

Originally I was planning to serve the blue ice cream with a sour one and had hoped that by mixing the two it would change color. As you can see in the first picture, this didn't go to well. The effect is hard to see, but since I really like the taste of the ice cream I will share the recipe underneath. Maybe by using more lemon juice it would work better, but since the effect is already quite subtle with pure lemon juice I doubt it.

So I decided to go with the original approach and sprayed lemon juice onto the ice cream. The fun thing about this is that in order for the effect to kick in you will have to wait a short while (otherwise you could just use a red dye to spray onto it...). In case you are wondering, the taste of the lemon juice goes really well with the ice creams.

Another thing you could do is to use a paintbrush and apply the lemon juice directly to the ice cream, like I have done in the title image.

If you have any other ideas how to serve the ice cream, please let me know.

Sour ice cream:

Ingredients:
3 cups of greek yoghurt
3/4 cup of sugar
1/2 cup of lime juice
pinch of salt

Preparation

Once again the preparation is really easy. All you need to do is to combine all the ingredients, mix them until most of the sugar is dissolved and let your ice cream maker do the work.