Dolomitic lime in juice clarification: the role of magnesium that calcitic lime lacks

Liming is one of the oldest and most critical operations at the mill: adjusting the juice pH to precipitate impurities and clarify it. The question rarely asked is which lime to use — and the difference between calcitic and dolomitic lime is not only in the calcium.

What magnesium does in the juice

Dolomitic lime supplies, besides calcium hydroxide, magnesium hydroxide. Mg(OH)₂ has solubility and kinetics different from Ca(OH)₂, and it takes part in forming the precipitates that drag colloids and non-sugars down during settling. The goal sought is a clarified juice with good settling speed and well-defined mud. Classic industry studies (such as Cesar & Caruso, published in Revista STAB in 2003) discuss the effect of magnesium on clarification and juice quality.

The evaporator question

Scaling in the multiple-effect evaporators is one of the mill's biggest hidden costs — it reduces the heat-transfer coefficient and forces cleaning stops. The chemical composition of the scale depends on many process factors (silica, phosphates, calcium oxalate, juice hardness), and lime is only one of the actors.

It is important to be technical here: dolomitic lime is not an isolated cause of scaling, and the nature of the deposits usually points to the process chemistry as a whole, not to a defect of the lime. The choice of lime influences the type of scale formed, but attributing all scaling to it is a simplification that does not hold up under analysis.

Magnesium in fermentation

In the distillery, magnesium is a cofactor of enzymes in the yeast's glycolytic pathway. There is technical discussion in the sector about the magnesium supplied via treatment lime and its effect on the wort — a point that deserves case-by-case evaluation, with data from the process itself, and not generic claims.

Calcined, always — but the quality of the calcination matters

Liming uses lime (calcined rock, hydrated or quick depending on the mill). What separates good lime from mediocre lime is reactivity and available CaO/MgO — a direct function of how the rock was calcined. Under-calcined or over-calcined (dead-burnt) lime reacts poorly and consumes more material for the same effect. That is why calcination control and a report per batch are not a luxury: they are what guarantees predictable dosing in liming.

Our dolomitic lime for mills has controlled reactive magnesium and available CaO, XRF analysis per batch and biomass-fired production. The positioning is technical and honest: we take the discussion to performance in the mill's process — clarification, settling, scale behavior — and not to promises the assay cannot back up.