Lactase Dosage in Gelato: How Much Enzyme, How Long
Table of contents
Adding lactase to a gelato base is not a substitution, it is a chemical edit to a sugar you already had. The lactose does not leave. It splits, and the two halves behave nothing like the whole. Dose it without rebalancing and the product turns sweeter and softer than you asked for.
What the enzyme actually does to your mix
Lactase, properly beta-galactosidase, hydrolyses lactose into its two monosaccharides, glucose and galactose, in equal parts. That is the entire reaction. No sugar is added and no sugar is removed, which is why the total solids of the base barely move.
What moves is everything that depends on molecule count and molecule identity.
Anti-freezing power roughly doubles for that fraction. Lactose weighs 342 g/mol. Glucose and galactose weigh 180 g/mol each. Freezing point depression is colligative, so the same mass now supplies two dissolved particles where it supplied one, and it depresses the freezing point roughly twice as hard. This is the identical arithmetic that gives inverted sugar its high PAC, applied to the milk sugar instead of the cane sugar.
Sweetness rises sharply. Lactose is the least sweet sugar in the dairy pantry, conventionally placed near 16 on the scale where sucrose is 100. Glucose is commonly cited near 70 to 75 and galactose near 32 to 35. Split the lactose and the same mass tastes roughly three times sweeter than it did. In a base carrying serious MSNF, that is not a subtle shift.
Sandiness risk disappears. Lactose is poorly soluble and crystallises out of high-MSNF mixes during storage, which is a leading cause of sandy, gritty texture. Glucose and galactose are far more soluble, so a hydrolysed base is structurally immune to that particular defect. This is why some shops hydrolyse bases that have no dietary requirement at all.
Browning increases. Both products are reducing sugars and more reactive than lactose, so a hydrolysed base picks up more Maillard colour through pasteurisation. Expect a faintly deeper cream tone and a cooked note in pale bases.
The two dosing protocols
There is no universal percentage, because enzyme preparations are sold by activity rather than by weight. What you actually choose is a combination of time and temperature, and the dose follows from it.
Warm hydrolysis. Hold the milk at roughly 35 to 40 degrees Celsius for one to two hours. Neutral lactase from Kluyveromyces lactis, the standard dairy preparation, works fastest near that temperature and near the natural pH of milk. Lower enzyme dose, tighter control, but it costs you a dedicated holding step.
Cold hydrolysis. Dose into refrigerated milk at 4 to 8 degrees Celsius and hold overnight, typically 15 to 24 hours. The enzyme works far more slowly at that temperature so the dose goes up, but the step costs no equipment time and folds neatly into a normal production day.
Quick reference. Warm and fast, or cold and slow. The enzyme is denatured by pasteurisation, so hydrolyse before you pasteurise if you want the reaction stopped and controlled.
The sequencing question matters more than most shops realise. Pasteurisation denatures the enzyme, so the order you choose decides whether the reaction has a defined endpoint.
Hydrolyse first, then pasteurise. The reaction runs to a known point and is then stopped cold. You know what you are balancing because the sugar profile is fixed before the base is built. This is the controllable option and it is the one to default to.
Pasteurise first, then dose into the ageing tank. Tempting, because maturazione already gives you hours at refrigeration temperature and the step looks free. The catch is that nothing stops the reaction. Residual active enzyme keeps working through storage, so the sugar profile, and therefore the serving hardness, drifts over the life of the base. Acceptable if you churn same-day and consistently. A problem if you do not.
How much enzyme, and why nobody can give you a percentage
Commercial lactase is specified in activity units, usually Neutral Lactase Units per gram, and preparations vary widely in concentration. A dose that is correct for one supplier can be several times off for another at the same weight. Any blog post quoting a flat percentage of mix is quoting one supplier's product without saying so.
The correct procedure is unglamorous. Take the activity specification and the recommended dose from your supplier's technical data sheet, which will be given against a stated temperature and hold time. Match it to whichever protocol above fits your production day. Then verify, because the data sheet assumes ideal conditions and your cold room is not one.
| Variable | Pushes dose up | Pushes dose down |
|---|---|---|
| Temperature | Cold hydrolysis at 4 to 8 C | Warm hold at 35 to 40 C |
| Hold time | Short window before pasteurisation | Overnight or full maturation |
| Target conversion | Full hydrolysis for a lactose-free claim | Partial, for texture benefits only |
| Base composition | High MSNF from skim milk powder | Standard whole milk base |
Partial hydrolysis is a legitimate target and an underused one. If the goal is suppressing sandiness and softening a stubborn base rather than making a dietary claim, a partial conversion gets you most of the texture benefit at a fraction of the enzyme cost and a fraction of the sweetness disruption.
Rebalancing the recipe afterwards
A hydrolysed base is a different recipe wearing the same name. Three corrections, in order of how much they matter.
Take sugar out. The sweetness gain is real and it lands on top of your existing sugar load. Reduce added sucrose to bring perceived sweetness back to where it was, and remember you are removing sweetness while leaving the solids that sucrose was also providing.
Take PAC out. The doubled anti-freezing power of the lactose fraction pushes the whole mix softer at case temperature. If the base already ran near the top of its PAC range it will now serve slack, which is the mechanism behind gelato that is too soft. Pull back the high-PAC sugars first, dextrose and invert, before touching anything structural. Run the corrected blend through the PAC calculator rather than estimating, and rebuild the sheet using how to balance a gelato recipe.
Restore the solids you removed. Cutting sucrose leaves a hole in total solids. Fill it with something that carries dry substance without sweetness or softness, which in practice means a low DE starch hydrolysate. The choice is governed by dextrose equivalent, and a maltodextrin under DE 20 is the usual answer.
Verifying conversion, and what you may claim
Two separate questions, and shops conflate them at their peril.
Did the reaction finish? Residual lactose is measurable. Enzymatic test kits and lactose test strips are the practical shop-floor tools, and a laboratory assay is the defensible one if a claim depends on the answer. Do not infer conversion from taste; sweetness rises well before hydrolysis is complete.
May you call it lactose-free? That is a regulatory question, not a technical one, and the answer depends entirely on where you sell. A threshold of 0.1 g lactose per 100 g is the figure most commonly cited internationally, but the definition, the wording permitted and whether a claim is allowed at all vary by jurisdiction and change over time. Confirm the current rule with your local food authority before the label is printed.
One point carries real consequence: hydrolysis does not remove the allergen. Lactase acts on the sugar and leaves the milk proteins, casein and whey, entirely intact. A lactose-free gelato is still a milk product and must still be declared as such under allergen labelling. Someone with a milk protein allergy cannot eat it, and conflating the two on a display card is a serious error rather than a marketing simplification. Where the requirement is genuinely allergen avoidance, the route is a plant-based formulation, not an enzyme.
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