If you freeze quickly, you get small ice crystals, resulting in small pores. There is a limitation in the size of the products, as large products take a long time to freeze. Another way is to adapt the formulation such, that the glass transition will shift. If you add mixtures of sugars, you can shift the glass transition Tg' and will get different crystal sizes. For example with the high Mw maltodextrin. A much larger part is not ice crystals now, but remains unfrozen in the glassy matrix. Hence, the crystals remain smaller.