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Lash (kneading) is forbidden on Shabbath. The question is whether mixing powdered baby formula with water on Shabbath falls into the catogory of kneading, which would cause it to be forbidden to be made on Shabbath.
The nature of the baby formula powder is that when it is mixed with water it does not solidify like flour that is kneaded but rather, it melts in the water. Therefore, this does not appear to fall into the category of kneading. Nevertheless, one should not add only a little water to the powder to begin with, but rather should pour onto it a substantial amount of water, more than the quantity of the powder itself. When it is done in such a manner, there can be no concern about kneading.
In addition, there can be no issue about the hot water cooking the powder on Shabbath, since the powder is already fully pre-cooked and we apply the concept that there is no "cooking after cooking" with regards to food that is dry, as is the case with this powder.
(See Ohr Lesion vol.2, 33: 8)
