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How to calculate FPDF (PAC)
Learn the science behind making soft, scoopable ice cream.
What is FPDF?
FPDF (Freezing Point Depression Factor) is also known as PAC (Potere Anti-Congelante, italian for Anti-Freezing Power). It measures an ingredient's ability to lower the freezing point of water in ice cream. Without freezing point depression, ice cream would be solid as a block of ice.
The most common way to make ice cream softer is by adding table sugar. This works to an extent, but often results in ice cream recipes which are too sweet. This can be remedied by utilizing ingredients with more anti-freezing power. In order to create a balanced recipe with great texture, it's important to know the FPDF of all ingredients.
To compare the anti-freezing abilities of different ingredients, we use the FPDF value. Sucrose (table sugar) is benchmarked at 100% FPDF. Another commonly-used sugar, dextrose, has more powerful anti-freezing properties with an FPDF of 190%.
Most sources display FPDF as a unitless value (100 for sucrose, 190 for dextrose) but here it's shown as a percentage to clarify that the value is a multiplier against sucrose.
What kind of ingredients affect FPDF?
- Sugars have differing effects on FPDF depending on size of the molecule.
- Dextrose (a form of glucose) is commonly used in ice cream recipes because it has nearly double the anti-freezing power of sucrose and is slightly less sweet.
- Allulose is a popular sugar substitute because it has similar properties to dextrose, but only a tenth of the calories. Be careful not to exceed 20 g per serving, because excessive amounts can cause digestive issues (source).
- Salt is a powerful anti-freezing agent (585%), but you can't add too much before affecting the flavor negatively.
- Alcohol is one of the strongest freezing point depressants (740%) and is commonly used to soften a recipe in small quantities.