1- Is there a minimum shiur to the prohibition of lash? Does the thickness of the resulting mixture, have to be detectable or just by definition if it’s made thicker it would be lash? (i.e. adding small amount of powder to a mixture)
2- Can one make tehina on Shabbos from the concentrate since this is making a thicker mixture?
3- Would making chocolate milk on Shabbos be ok and why?
Answer:
If the mixture remains a liquid after powder is added, meaning that it does not gain a thick dough-like consistency, there is no issue involved in making the mixture. Therefore, there is certainly no prohibition in preparing chocolate-milk on Shabbos, because the resulting mixture has the consistency of a liquid.
Tehina is made from a paste, to which water and lemon juice etc. are added. At first glance, this does not involve any prohibition of lash (kneading), because the thick paste actually becomes thinner (see Biur Halachah 321:15). However, Shemiras Shabbos Kehilchasah (8:26) prohibits preparing tehina, because of an interim stage when the mixture becomes harder, which is considered kneading.
Yet, some rule leniently concerning preparing tehina, for a number of reasons:
1. We do not look at the interim stage, but only at the final product, whereby a thick mixture is made thinner.
2. According to some Rishonim (Rashba), the prohibition does not apply right before the meal.
3. According to some authorities, there is no prohibition of kneading after a dough has already been kneaded (Shulchan Aruch 321:15; see Chazon Ish).
Therefore, some permit preparing tehina on Shabbos, if a shinui is made in mixing it (for instance, mixing in criss-cross action rather than bringing the spoon round), and if it is prepared right before the meal.
Although one should prepare the tehina before Shabbos, there is therefore room to rely on the lenient opinion where there is a need.
See also Menushas Ahava Vol. 2, 9:17.
