There is no prohibition of Lash for food that has been mashed. Since it has already been mashed and softened, the act of kneading does not fundamentally change it. Therefore, one may mix a dish of meat, potatoes, and barley that have fallen apart, and one may even add water to the mixture to form one mass. One may also add gravy to mashed potatoes and mix them together. Since the potatoes are already mashed, there is no prohibition of Lash (Responsa Rambam as quoted in Beit Yosef 321:19).
If a mixture was made before Shabbat but some liquid gradually separated from it, it may be mixed again on Shabbat since there is no prohibition of Lash for something that has already been mixed. Since all permit this, it is unnecessary to use a shinui, but one should still stir more slowly than on a weekday. For example, if oil has risen to the top of an eggplant salad, it may be mixed back in with the eggplant. Similarly, if peanut butter separated and there is oil floating on top, it may be mixed back in.
Many poskim seemingly allow adding ingredients to a mixture that had been prepared before Shabbat. However, some are stringent. Therefore, the ingredients may be added with a shinui. For example, hot sauce may be added to hummus as long as it is mixed with a shinui. Similarly, if an eggplant spread was prepared before Shabbat and mashed in its juice, mayonnaise may be added to it on Shabbat with a shinui (see SA 321:15-16). We have already seen (in the previous section) that the shinui can involve moving the spoon back and forth in straight lines or perpendicularly when stirring. If this is not a recognizable change, the spoon should be removed from the mixture entirely after the completion of each stirring motion.
One may mix cake crumbs with soft cheese or milk, since the crumbs were already kneaded when they were made into cake, and thus the prohibition of Lash no longer applies. However, some are stringent and maintain that once the baked item has been crumbled, the original act of kneading has been nullified. Therefore, one should mix the crumbs with a shinui, and do so only for immediate consumption.
Another important principle is that Lash involves taking dry, discrete materials and binding them together. However, if the dry ingredients spread throughout the liquid to which they are added, this is not considered Lash. Therefore, one may add herbs to soft cheese, since the herbal leaves spread out and do not clump together. Similarly, one may mix granola into soft cheese, since the granola bits do not join together and become one mass, but rather adhere to the cheese. One may also mix strawberries or bananas with cream, since the pieces do not bind and become one. One may add sugar or cocoa to soft cheese, because the aim is not to bind the granules of sugar with the cocoa but rather to flavor the cheese.
The Aĥaronim debate whether one may mix two viscous foods like soft cheese and honey. Some maintain that since they form a new thick mixture, it is considered Lash (SSK 8:16). Others maintain that the prohibition of Lash exists only when mixing dry ingredients with wet ones, while one may mix two wet ingredients together (Igrot Moshe, OĤ 4:74). In practice, one may mix the two foods with a shinui.