Kneading, the av melachah of losh, is forbidden on Shabbat. The melachah encompasses all activities which, like kneading, join small particles into one mass using liquid, and applies to both foods and non-foods. It also includes later treatment of dough, like basting or braiding.1

Kneading invariably involves two steps: a) Pouring the liquid into the flour; b) Mixing the flour and water together to make a dough. There is a Talmudic dispute regarding what exactly defines losh.2 Rebbi says that just pouring the liquid over the flour is already losh, since the flour and water fuse on impact. Kneading them together is also Biblically forbidden, but as an independent, additional transgression. Rabbi Yosi Bar Yehuda, however, says that one only transgresses losh by mixing the ingredients together and not by merely pouring the liquid over the flour. While some halachic authorities, most notably Sefer Hateruma, follow Rebbi’s interpretation, the vast majority side with Rabbi Yosi.3

There are a variety of substances that can be kneaded with liquid. Some, like fine flour, completely mix with water to the extent that the flour becomes a different entity—dough. These substances are halachically termed “bar gibul.” There are other substances which are not kneadable, like oats or finely diced vegetables. When these are mixed with water they just clump together but don't transform into a new entity. These are called “lav bar gibul.” It is apparent that Rabbi Yosi’s ruling applies to bar gibul substances. The authorities debate, however, what he would say about kneading lav bar gibul substances.4 Maimonides asserts that since one can’t truly knead lav bar gibul ingredients, Rabbi Yosi would rule that one cannot Biblically transgress the melachah of losh with them, since the second step of kneading isn’t done.5 Accordingly, mixing them would only be rabbinically forbidden. Conversely, Tosafot maintains that since they are not kneadable, the second step is not applicable, and one Biblically transgresses losh simply by pouring liquids on them.6

Losh is only Biblically forbidden if done with a “belila ava” - a thick dough-like mixture which is not pourable. “Belila raka” - pourable mixtures, like dressings and dips, are only rabbinically forbidden.

It is extremely relevant whether a transgression is Biblical or rabbinic. One way to avoid a prohibition on Shabbat is to do the act in an unusual way. (Note: one cannot decide on one’s own to do a forbidden act in an unusual way to avoid the issue. We follow the examples given by the sages.) If an act is only rabbinically forbidden, it is easier to apply the leniency. Also, a rabbinic prohibition will sometimes be waived in situations where the Sages felt it should not apply. For example, according to those who maintain that just pouring the liquid into the flour constitutes losh, there is no permissible way to make a belila ava on Shabbat, since there is no method of pouring unusual enough to permit a Biblical transgression.

Although most authorities follow Rav Yosi, the Rama7 writes that one should be stringent and take into account those who follow Rebbi. Practically, this means that whenever possible one should prepare a belila ava before Shabbat regardless of whether it is bar gibul or not. If the food won’t last when prepared the day before, in some cases one can be lenient and prepare them on Shabbat, provided it is done in an unusual way. For example, guacamole can be prepared on Shabbat but one should first put the lemon juice in the bowl before adding the avocado since this differs from the way it is normally done. Obviously, if one normally prepares it that way during the week he or she should do the opposite on Shabbat. One should also change the method of mixing, by using gloved hands or using a fork and making criss-cross movements. Note: there are many factors to consider and what is permissible with one food may not be by another, so each case should be treated individually.

If the mixture is a belila raka then one may always mix it using the same unusual methods described above. A useful tip suggested by the halachic authorities for one who wished to make a belila ava is to add extra liquid and make it a belila raka which allows for more leniencies.

If the mixture was kneaded already before Shabbat, one may add liquid on Shabbat and stir it gently. This is because the additional liquid actual makes the mixture less bonded together. Some authorities maintain that if the foods are cooked they are not subject to losh.8

Toladot

Mixing sand or earth with liquid.9

Losh in the Mishkan

Flour was kneaded with water to produce the showbread, the lechem hapanim.10 Also, the dyes used in the mishkan were produced by mixing ground herbs with water and making it into a paste.11

Common activities to avoid

● Making baby cereal or instant porridge in the usual way12

● Making a thick salad dressing in the usual way

● Mixing water and sand, and shaping sandcastles