I recently found out that a friend of mine likes to make 4-stranded challot where half the strands are made from whole wheat flour, and half are made from white flour. This, of course, made me think. Suppose she uses 1 kilo of whole wheat flour and makes that dough. She then uses 1 kilo of white flour and makes that dough. The doughs are designed to be separate, and neither dough is itself chayav in challah, even without a bracha, as each is only 1 kilo of flour. However, the two doughs will ultimately be put together to form unified challot. If they are counted as mitztarfim, then they are definitely chayav in challah, with a bracha. Assuming she only has 1 kilo of each flour and can’t make 2 kilo worth of each dough (or even 2 kilo of one of the doughs) in order to remove safek, would she take challah (with a bracha) or not take it at all? Thank you so much for your help, and I look forward to hearing from you!
ב"ה Shalom Your question is very much in place, since there is discussion in Halacha of dough put together from different batters. The poskim discuss what is to be done when a person makes two separate batters such as one sweet and one unsweetened or one with spices and the other without spices, even if they touch later and the touching doesn’t matter. Are they to be considered together in order to take Challa? On the one hand some say that the separate batters are what makes them separate even if they touch, and if there is not a big enough amount to require Challa in one batter, then challa need not be taken. on the other hand, some say that as long as they touch, even if they were made as separate batters, then the two combine and Challa is required. Due to this difference of opinion, the common minhag is to take Challa but without a Bracha. Therefore, in summary, in this case with the separate batters are eventually braided together as one loaf, Challa should be taken but without a Bracha. All the best (שו"ע, יו"ד סי' שכ"ו: א, ערוך השולחן יו"ד סי' שכו סעי' ו, חלת לחם סי' ה ס"ק טז, חלה כהלכתה סי' ח סעיף ט))