PAC and POD: why ice cream is soft and how sweet it tastes

Why is one homemade ice cream rock hard after a night in the freezer, while another can be scooped straight away? Most often it’s not the fat or the machine, but the sugars: how much there is and what kind. Ice cream makers describe this with two numbers from Italian — PAC (potere anticongelante, anti-freezing power) and POD (potere dolcificante, sweetening power).

Why sugar softens ice cream

Dissolved substances lower the freezing point of water. According to Douglas Goff (University of Guelph), this is a so-called colligative property: what matters is the number of dissolved molecules, not their weight. The smaller the molecule, the more of them there are in one gram and the more they lower the freezing point. That’s why simple sugars (glucose, fructose) soften ice cream more than the same amount of ordinary sugar (sucrose), whose molecule is about twice as large.

As the water in ice cream freezes, the sugars stay in the remaining liquid, which becomes more and more concentrated, and its freezing point keeps dropping. That’s why ice cream never freezes completely: according to Goff, at −16 °C only about 72 % of the water is frozen. The rest is a thick syrup between the crystals — and that’s what makes ice cream scoopable.

PAC and POD in brief

• PAC tells you how strongly a substance lowers the freezing point compared with the same weight of sucrose. Sucrose = 100. Dextrose, with a PAC of 190, softens almost twice as much.
• POD tells you how sweet a substance is compared with sucrose. Sucrose = 100. Dextrose, with a POD of 74, is less sweet.

For a mix, both numbers are expressed as grams of sucrose per 100 g of mix that would have the same effect. zmrzka calculates PAC including lactose from milk (it makes up about 54 % of milk solids non-fat). Exactly how is described in the article How zmrzka calculates the composition.

Table of coefficients

Values are on a dry basis unless stated otherwise. Those marked “calculated” are derived from molar mass; where marked “approximate”, sources disagree.

Source: the sweetener table from Goff & Hartel, Ice Cream (7th ed., 2013); polyols, alcohol and salt calculated. For salt, zmrzka uses the more cautious value of 585.

What PAC is right

We have to be honest here: while preparing zmrzka we were unable to find verified target PAC values for specific temperatures. Italian “PAC by display-case temperature” tables are widely cited, but we couldn’t verify where they come from. We do, however, have calculations from proven recipes:

• Goff’s industrial mix with 12 % fat, served at −15 to −18 °C, comes out at a PAC of about 21.
• A homemade vanilla ice cream from the Ice Cream Science blog, served at around −15 °C, comes out at about 22.5.
• Sorbets from proven recipes come out at 27–32.

For serving straight from a home freezer at −18 °C, it makes sense to raise the PAC slightly; for a display case at around −12 °C (gelato), to lower it. The bands on zmrzka (for example 22–34 for cream ice cream) are therefore approximate.

In practice, POD is kept at roughly 16–20 g of sucrose equivalent, but this number isn’t verified from a primary source either. Goff’s mix comes out at a POD of about 15.

How to soften ice cream

Dextrose in place of some of the sugar

The simplest route. If you replace 30 g of sugar with 30 g of dextrose in 1 kg of mix, the PAC rises by about 2 points and the POD falls by about 1 point. The ice cream will be softer and slightly less sweet. Goff and Hartel recommend that dextrose and fructose make up at most 40 % of all sugars, otherwise the quality suffers.

Invert sugar and honey

They contain glucose and fructose, so they soften much like dextrose, but they are sweeter. Goff and Hartel give upper limits: honey at most 45 % and invert sugar at most 30 % of the sugars. Invert syrups in the shops differ in their degree of inversion — the figures on the label take priority.

Alcohol

Ethanol has a very high PAC. For example, 20 g of a 40 % spirit contains about 6.6 g of ethanol, which raises the PAC of 1 kg of mix by almost 5 points (our own calculation). David Lebovitz recommends at most about 3 tablespoons of spirit per litre of mix, otherwise the ice cream won’t freeze. For ice cream sold in Slovakia and Czechia, the limit is 3 % alcohol.

Salt

In theory it softens more than anything else, but you can only use a pinch — any more and you’d taste it. In salted caramel or pistachio it helps the flavour more than the texture.

Polyols

Erythritol and xylitol have a high PAC and a low energy value. Above 10 % added polyols, however, a product in the EU must carry a warning about a laxative effect, and for erythritol EFSA set an acceptable daily intake of 0.5 g per kilogram of body weight in 2023. Xylitol is also highly toxic to dogs.

Try it out on the recipes — each one shows its PAC and POD, and they are recalculated when you change the ingredients.