Is chimutz a wholly physical phenomenon?

Question

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?

Answer 1

See THE LAWS OF PESACH BY RAV DAVID BROFSKY from etzion.org.il

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.