The gemara seems to imply that chametz is not a concern with flour mixed with fruit juice. Indeed, amongst other effects, sugars (which are present in fruit juice) slow gluten development. However, the physical processes in bread-rising are complex and easily affected by many factors (ingredient proportions, temperature, etc.). In addition, physical processes such as bread-rising are generally immediate and continuous , which means a certain amount of rising is not considered halachik chimutz.

Ultimately, is the concept of chametz to be treated as a purely halachik construct independent of the physical phenomenon of yeast/gluten interaction, or do we need to factor in modern scientific knowledge of the myriad influences on a physical process? Even if certain ingredients affect the chimutz-process, should we be able to estimate and adjust time-limits accordingly based on what would typically be the proportion of rising that would have occurred in a typical (ancient) bread by the time limit of the Talmud? Do any halachik sources discuss this issue, e.g. with regard to chametz nuksheh/matza ashira?

  • My rebbeim have said that the definition of chametz must indeed be related to a physical phenomenon, but we can't be sure what it is exactly, as chazal obviously didn't have the modern chemical terminology that we'd use to explain it today Apr 2, 2015 at 3:23
  • @Matt, great! Why not post that as an answer, citing your rebbeim?
    – msh210
    Apr 12, 2016 at 21:12
  • It seems you do not understand what is "slow gluten development." Glutain is what sticks together when you mix flower and water, if makes if possible for the bread to rise by not letting the gas out but holding it in the glutain as a rubber balloon (nice video of glutain)
    – hazoriz
    Apr 14, 2016 at 16:41
  • And "slow" means it does not sick together so easily, chomets seems to me either 1. the gasses in the glutain , not just glutain and not just the gasses or 2. The if a certain amount of gasses where produced or 3. If there is a certain amount of yeast cells or 4 a certain amount of alcohol produced. see youtu.be/ZXYZYKfjNBg , youtu.be/GvD-8ZfxfOY
    – hazoriz
    Apr 14, 2016 at 16:54
  • From the answer below if seems it is only when the gas is stuck in the glutain,
    – hazoriz
    Apr 14, 2016 at 16:56

1 Answer 1



First part of the quote is background.

Shiur #2: The laws of Pesach. Defining chametz. Two passages in the third chapter of pesachim discuss the definition of “chimutz” (leavening). one passage (pesachim 48b) presents the physical characteristics of chametz. the mishna describes the leavening process as follows: first, the dough becomes pale, similar to the appearance of a man whose hair stands on end out of fright. next, cracks begin to develop on the dough’s surface, described by the mishna as “karnei chagavim” (locusts’ antennae). the cracks then begin to increase and merge into each other.

This part of the quote is the main point:

The Rishonim and the Shulchan Arukh (451:2) rule in accordance with the Sages (and R. Meir) regarding the definition of chimutz. it is forbidden and punishable by karet to eat the mixture once it has developed cracks like a “locust’s antennae.”

R. Yosef Karo, in the Shulchan Arukh (459:2), concludes: One should not leave dough without it being worked, even for a moment. as long as one is working the dough, even for the entire day, it does not become chametz. If one left the dough without working it for a mil, then it becomes chametz. the period of a mil is 18 minutes.

From this we see that the halachic status of chimutz is specifically related to the appearance of the dough and not to some chemical status. The chemical fermentation process of leavening will continue while the dough is being worked.

So yes, the concept of chametz is to be treated as a purely halachik construct which is not defined by the "physical" (I prefer to call it "chemical") fermentation. Nevertheless, chimutz cannot occur unless there is this fermentation.

  • 1
    I would say that means that it is indeed a physical construct, but one that needs to be visible to the naked eye.
    – Loewian
    Apr 13, 2016 at 13:50
  • But the Orez can be mixed to 5 minim and complete shiur. Mishna chala 3, 7; 3, 10; Gemara brachot 37a. It seems as if the Seor has a catalytic effect on Rice (following Rashi). Corn do not contain Gluten. All 5 minim contain gluten?
    – kouty
    Apr 13, 2016 at 18:51
  • Where is your source that the chemical fermentation process of leavening will continue while the dough is being worked?
    – Aaron
    Apr 13, 2016 at 20:40
  • @Aaron- I think that it is everyday chemistry that agitation of the ingredients does not stop a chemical reaction. (I have studied chemistry to a high level.) Apr 13, 2016 at 20:47
  • 1
    @Gizbar Thank you - a nice idea. The interpretation or reasons that we think we have for a mitzvah are limited by our human minds. G-d may well have deeper thoughts and reasons. Therefore we cannot use our interpretation or reason to develop halacha. So I would rephrase your comment to: We maybe can understand why as long as you're kneading it's still good from the concept that chametz parallels the trait of Zeal in doing mitzvot. Jun 10, 2016 at 8:08

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