Skimmed milk powder (SMP): the solid that gives structure

Skimmed milk powder, which I often abbreviate as SMP, is an extremely technical ingredient. It is the main ingredient that adds non-fat milk solids, and in gelato making it does an enormous job. It doesn't add much to the flavour if we exclude the taste of fior di latte, but it is a key ingredient for giving body to ice cream. Without it, the ice cream is empty and icy, and it has many technical uses in milk-based flavours. Let's look at them together.

On the market there are whole, partly skimmed and skimmed (1%) milk powders. The truth is that in gelato making the choice almost always falls on skimmed milk for convenience: being almost fat-free it keeps better and doesn't risk going rancid like the others. Especially for home use, where a 1 kg bag can stay open for a long time given the small quantities used, the others are not practical options.

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Why it's used in ice cream

The non-fat components of milk are also present in other ingredients (milk contains about 9%, cream 6%), but the most concentrated and practical source to manage is precisely milk powder. Within the mix, skimmed milk powder does three fundamental things:

• retains water: thanks to lactose's high absorption power it reduces free water, and therefore the risk of ice crystals forming
• gives body and structure: makes the ice cream more compact and full
• helps whipping: promotes the incorporation and retention of air

What's inside: the main components

Lactose

It's a sugar and as such it slightly delays freezing with a mild anti-freezing power (PAC of 26) and it isn't very sweet (low POD of 16). Its main quality is absorbing up to 10 times its weight in water: an advantage for binding free water, but also the biggest risk, because in excess it «drains» the other solids and in excess gives a sandy consistency.

Proteins

Casein, lactalbumin and lactoglobulin are excellent emulsifiers: they prevent water and fat from separating, improve texture, add creaminess and help incorporate air. Casein makes up about 80% of the proteins in milk powder.

Effect on flavour and texture

On flavour, SMP is discreet: it doesn't impose a taste of its own, at most it rounds things off and gives that milky background note. On texture, however, it's a leading player: it's one of the main contributors to creaminess and the «full» sensation in the mouth. Well dosed, it's the difference between an ice cream that caresses the palate and one that seems like frozen water.

The risk of overdosing

Too much SMP means too much lactose, which absorbs more water than needed and leaves the other solids dry: the result is a «dry» and «sandy» ice cream. It's the classic mistake of those who, to add body, overdo it with the powder.

Keep in mind the general recommendation suggested by Angelo Corvitto in his book «The secrets of ice cream»: no more than 10% milk powder in the mix. That 10% provides about 5% lactose, able to absorb 50% of the water without causing problems.