- Caking

By Bento, Luis San Miguel
Posted on 2006-09-19    Last edited on 2009-12-09

During storage, sugar crystals, in certain conditions, may agglomerate forming hard blocks of sugar that can attain considerable dimensions. This occurrence is due to dissolution and re-crystallization of sugar with bridges formation between crystals. This phenomenon is named caking. 

After crystallization and centrifugation, a syrup layer is maintained surrounding sugar crystals. Depending on drying conditions, and syrup purity, a mass of amorphous sugar is formed at the syrup surface. Between the amorphous layer and the crystal, syrup is entrapped. During conditioning the amorphous sugar is re-crystallized and water is released. This water is removed with a current of  dry and hot air up-flowing in the conditioning silo.

If the sugar re-crystallization happen during storage, sugar caking occurs and big lumps of sugar may be formed.

Caking can also occur when sugar is stored hot (higher than 40 C). When this sugar is placed in contact with cold surfaces, as the floor or the silo or store walls, a temperature gradient will occur. This temperature gradient will produces a water vapor pressure gradient. Consequently, vapor will migrate from the interior of the sugar pile to the exterior. Consequently, near the cold walls the water will condensate and sugar will be dissolved. If storage condition change, temperature and or humidity, re-crystallization can occur and sugar can form lumps (caking).

Except when sugar is produced and commercialized in lumps, caking is highly undesirable.