If one would like to bake matzo or use flour to make a Passover food, how long do we have for the process to take place?

If 18 min, then is that 18m59s or 18m00s?

If the food is cooked before 18 min, but is left in oven, is it considered kosher since it was cooked before 18 minutes elapsed?

  • It's 18 minutes, but good question whether the beginning or end of 18. I looked but couldn't figure it out. As for the last question, i'm pretty sure that it becomes chametz if left in the oven.
    – Scimonster
    Commented Apr 6, 2015 at 7:20
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    The actual baking takes well under 18 minutes. The whole process has to be done by the time 18 minutes have elapsed since the water came into contact with the flour.
    – Daniel
    Commented Apr 6, 2015 at 11:50
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    ...assuming it was not kneaded, @Daniel. (IINM. CYLOR.)
    – msh210
    Commented Apr 6, 2015 at 17:43
  • @Scimonster That would mean you can't heat up matza.
    – Double AA
    Commented Apr 6, 2015 at 18:23

2 Answers 2


The Gemara in Pesachim 46a (brought in the Rambam Laws of Chametz 5:13 and the Shulchan Arukh OC 459:2) says that if one leaves dough for the length of time that it takes to walk 1 "mil" (a Talmudic unit of distance) then it becomes Chametz. Opinions regarding the time it takes to walk a mil vary from 18-24 minutes, and here the Shulchan Arukh is strict to take the shorter time: 1/5 of an hour + 1/20 of an hour = 18 minutes 0 seconds.

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    @msh210 so if the dough is not "left" but rather kneaded, that is not counted within the 18 minutes....?
    – alice fine
    Commented Apr 6, 2015 at 19:09
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    @alicefine According to Rambam, the time of kneading is not included in the 18 minutes. He says one can knead the dough all day and it will not become chametz. The Shulchan Aruch agrees with Rambam, although the Rosh has certain reservations. You can read more here: etzion.org.il/vbm/english/archive/moadim70/02-70moed.htm Commented Apr 7, 2015 at 7:43

I shall split the answer up. One first makes the dough as I wrote as big as there is room in the oven. One should use a 'pin' a kind of metal or wooden hinged bar to 'bang' it down. Then one should cut it with a knife (according to the r'mo but not kept) and give it out to the 'rollers' called velgerers. The most important and only thing mentioned in the gemoro is heat. One has to be careful to keep it cold. Once it gets worked on and warm the 18 minutes does not apply. Before one starts one has to immerse ones hand in cold water (not kept today) to make sure its really cold. Washing negel vasser isnt good enough. One holds it with only two fingers (thumb and forefinger) not the whole hand and starts to knead it. The way to do it is holding it up again with two fingers from one hand and carrying on squashing it down with the other. This is the only way one can work with the 'whole' dough at once all the time. Each time you squash it down you are squashing the whole dough not just part of it. To be continued if found to be interesting.

The whole idea of 18 minutes for becoming chometz is a mistake.

I am specially going to write how a hand matzo has to be made, since today it is rarely done correctly. Please forgive the length of this very important post.

The 'ran' (regarding the three women mishna system) writes that it has to be done as quickly as possible. That means if it can be done in 4 minutes and you take 5 minutes over it, that is not doing matzot correctly.

So you have to make a system which caters for that. Today no hand matzot which I am aware of do, against the 'ran' and all other poskim.

The kitsur writes that one makes a dough as large as the amount of workers you have. So you have to make sure you divide all of it out immediately. I would add to speed things up that one should not make a dough larger than there is room in the oven. So each matso gets 'done' in the least possible time.

When he feels the dough is ready he should do what is called 'aricha'. Shaping it round, putting all the folds and lines in the middle not leaving them on the outside which makes jagged edges and kfulos, turn it over flatten it a bit, and start to 'velger'. One starts 'from' the middle but not going over the middle and keeps going round and round lifting it up over the velger holz so it shouldnt stick, not velgering till the end otherwise it sticks, until it is ready. One doesnt turn it over in the middle and tries to keep the thickness even. If it is thinner in one place like in the middle it is likely to burn there. That is really all I have to say about the technical aspect of baking matzot. One should start slowly being very careful not to make kfulos and build up speed gradually. If one starts by being careful about kfulos one never makes them. It is not right do it quickly and then straighten out kfulos. One doesnt type at 100 wpm and then make corrections.

If you make kefulot and then iron them out it will leave a line or shirtut on the matso. One can often see many of these on the finished product. That proves that the person didnt know how to velger or worked too quickly. According to the r'mo one is not allowed to make kfulos specially and then iron them out because he may not iron them out properly. He talks about a whole matso but I would say this applies even to one kfulo. Another problem is that if one makes a kefulo you have to take it out with another stick from the oven, not being used for other matzot. Making jagged sawtooth edges is also prone to making kfulos in the oven, since they bend over each other while baking. Having a mashgiach to check matzos (they are not chickens) should be unnecessary for those who can velger properly, who anyway should be the only ones baking matzot. One doesnt use novice shochtim either.

The r'mo says during the tekufa one has to pour out all water. So what does one do with the 'mayim shelonu'. The special well water for matso.

He says one should put a metal object on a string and drop it into the water but should not use his hands since if he uses his hands this would heat the water.

I am sure on a thermometer you wouldnt notice any different at all, but still you have to be machmir with heat during baking matsot.

Our tekufot times today are not right. They should be the solstices.

They have four halachic considerations. When to say 'v'sen tal umotor. When to keep 'nittul' since he was born on the longest darkest night, and when to pour out water and also if one makes a leap year and when to say birchas hachamo.

carrying on. The 'story' of the three women in the mishna is that they had room for only one matso (which was then something very similar to a loaf of bread today), One started kneading the flour five minutes later she was up to the 'aricha' stage which can be translated as 'forming' the shape then the second woman started kneading. Five minutes later the first woman was up to baking the second up to forming and now the third started kneading. The idea being that not a second is wasted and each matso is done in the quickest time possible. The yerushalmi says after the 'forming' (ten minutes in my example) she also had to make the oven. In the olden times that was the hardest part. Each one had to make the oven separately when their dough was finished before baking it. It sounds like they left it lying without anything being done to it. Which would be against the shulchan aruch who says one it is ready for baking it must not be left for even one second! One must say that they poured cold water over it.

I dont understand the yerushalmi because it should have been the husbands of these three women who made the oven. The gemoro says that a poor man his wife bakes and he does the oven.

The mishne berura says that the rosh carried his matso quite a distance to the oven so how can the Shulchan Aruch say it becomes chomets straight away! My simple answer would be again that he poured cold water over it.

Coming back to the cold hands. The MB brings the Bach who says that during the kneading and forming even if your hands are cold you still have to wash them under cold water or immerse them. He brings others who say that is only if you are near the oven. But he finishes saying you have to be machmir. One sees from here how careful they were about heat.

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    Why are you splitting this up? Please edit this all into one answer (don't worry; it'll fit) and delete the partial answers. Thanks. Commented Apr 26, 2015 at 21:37
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    Since you have not responded to my prior comment by editing these into one answer, I will do so. I'm only going to cut/paste the other answers into this one; once I've done that I suggest that you edit further to clean it up. Having five separate-but-not-really-separate answers doesn't work well for the site. Thanks for understanding. Commented Apr 28, 2015 at 14:41

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