Turkish phyllo rolls split when the edge of the pastry sheet is not sealed, the filling is too moist or there is too much of it, or the oil is not hot enough. They can also open if they are placed in the oil with the seam facing up. Sealing the edge with flour or egg white, removing excess moisture from the filling, and keeping the oil at 170–180°C / 340–355°F largely solves the problem.
The first reason they open is a missing seal. Yufka is a dry pastry sheet and does not stick to itself; dampen the final edge of the roll with water, beaten egg white, or a thin paste made by mixing flour and water, then press it down. The paste makes the strongest seal. Press the sealed edge with your fingers for a few seconds so it holds. If the edges of the yufka have dried out, the seal will not hold; keep the sheets covered with a slightly damp cloth as you work. If the edges of an unrolled sheet have dried out and become brittle, trim them off.
The second reason is the filling. Moisture from the cheese in a cheese filling, the potatoes in a potato filling, and the onions in a ground-meat filling turns to steam during frying, and the steam looks for a way out. If the sealed edge cannot withstand that pressure, it opens and the filling runs into the oil. Drain the cheese first, mash the potatoes thoroughly and let them cool, and cook the ground-meat filling until its liquid has evaporated before using it. The filling should be warm or cold; hot filling wets the yufka from the inside and can tear it while rolling.
The amount of filling and the way the rolls are shaped also matter. Spread a thin line of filling along the wide edge of the yufka, leaving one centimeter of space on each of the 2 sides; too much filling makes the roll bulge and spill while frying. Fold the sides inward first, then roll it snugly without crushing it. A loosely rolled pastry opens in the oil, while one rolled too tightly cracks as it fries. Arrange the rolls on a tray with their seams facing down.
Oil temperature completes the picture. Keep the oil at 170–180°C / 340–355°F; at this temperature, the yufka quickly forms a crust and the seam seals shut. In cold oil, the rolls stay in the oil longer, the yufka softens, absorbs oil, and opens. Lower them into the oil with the seam facing down and do not touch them for the first half minute. Do not overcrowd the pot; the rolls should be able to float without touching each other. Drain the browned rolls on a wire rack rather than piling them on paper towels.
If you will not fry the rolled pastries right away, freeze them in a single layer on a tray and transfer them to a bag once frozen; fry them directly from frozen without thawing to further reduce the chance of opening. Pastries left in the refrigerator for hours absorb moisture and loosen. If one opens during frying, remove the filling pieces that enter the oil with a wire skimmer; crumbs left in the oil will burn and give the next batch a bitter taste. Cheese pieces that fall into the oil also make it foam. Strain the oil after frying; oil with crumbs left in it darkens quickly during the next use.