Ashkenazim are more lenient with regard to bishul akum (food cooked by non-Jews) and pat akum (bread baked by non-Jews) than Sefardim are. Ashkenazim mandate that a Jew light the fire (or tun on the stove or oven) that is used for cooking. If a Jew has done this then the food is considered bishul yisrael and the bread is pat yisrael. Sefardim are stricter and consider food bishul yisrael and bread pat yisrael only if a Jew did the actual cooking or baking.
I recently found a historical reason for this difference, based not on theology but on practical need.
Jacob Katz in Exclusiveness and Tolerance: Studies in Jewish-Gentile Relations in Medieval and Modern Times points out that early Ashkenazi communities were very small – too small to produce all the food needed for many households. (One must remember that there were no prepared or pre-trimmed and cleaned foods, meat had to be butchered, soaked and salted, wheat had to be cleaned, ground and then kneaded and baked, wine needed to be made, meaning grapes had to be cleaned and crushed, the wine making process started, the wine aged, etc., and there was no refrigeration and no chemical means other than salt and smoking to preserve food.)
Ashkenazim got around this problem by using a ritual fiction – the idea that one moment of lighting a fire was equivalent to hours of food preparation work. Sefardim, who lived in what were then the centers of Jewish life, had no need for these leniencies – therefore, their rabbis did not codify them.
But Katz has something more interesting to say about the subject. From the earliest times of Jewish presence in Europe and commonly through the 10th century, Jews got around the issues of bishul akum, pat akum, yayin nesach, etc. by owning slaves. According to Katz (p. 41-42):
…Jews bought slaves who they then circumcised and converted into 'half' Jews. In the event of manumission the slave became, with certain very slight reservations, a full Jew, and even while he was a slave he was for ritual purposes regarded as a Jew. He could handle the wine of his owner and do his cooking. Not so the Christian servant, to whom the restrictions of the segregative laws applied.
Who were these slaves? Pagan Slavs, whose name, Slav is the actual source for the words in most European languages that mean "slave." The areas Jews lived in were ruled by Christians who viewed pagans as less human, so to speak, than both Christians and Jews, so Jews were allowed to own pagan slaves. (Christians, it must be pointed out, were the primary slave owners by far.) Although Katz does not mention this, I've seen elsewhere that occasionally Khazars would be captured and sold on the slave market. Jews would buy them and set them free – pidyon shvuyim in action in its primary, pre-Internet petition form.
Something else Katz does not mention is the genetic effect of these slaves on Ashkenazi Jewry. I would suspect that slaves were frequently set free so Ashkenazi men could marry them. In the times before Rabbaynu Gershom's ban on polygamy, this may have been even more common.
An estimated 40% of Ashkenazim are traced back genetically to four 'founding' matriarchs who lived in approximately the year 1000. But 60% of Ashkenazim are not traced to these four women. That means, I think (but let C-Girl correct me if I'm wrong on the genetics, just as I hope S. will if I've erred on the history), that the Ashkenazi matriarchal population was quite diverse before 1000 years ago. The bottleneck represented by the four 'matriarchs' occurs about when Jewish slave-owning becomes rare.
How did a Middle Eastern people with predominantly brown skin and dark curly hair morph into a fair-skinned nation of auburn, blond and red-headed members? Sure, maybe the old saw is true and your ggggggg-grandmother was raped by a Cossack or a Crusader. More likely, I think, is slavery.
Yes, as the Haggadah says, we really are descendants of slaves – just a bit more recently than most of us realize.
UPDATE – C-Girl sent a link to a great piece in this week's Forward, My Forefathers Were Yurt-Dwelling Siberians, by Uzi Silber, who describes himself as a "glatt Jew" and who is descended from a long line of known Jews:
…It seemed I’d finally be able to certify my kosher pedigree linking myself inextricably to King David and the prophet Isaiah. And so it came to pass that I sent away for what may be, at $100, the world’s most expensive swab, which I then rubbed inside my cheek and returned to a lab in Texas.
My test results appeared on the Genographic Web site three months later. The result? This glatt Jew was a member of a certain Haplogroup Q.
Who, you might ask, is a Q?
Q, it turns out, is a branch of humanity that arose about 20,000 years ago with “a man born in the savagely cold climate of Siberia.” In other words, I am a direct descendant not of a swarthy Judahite shepherd or Galilean Bronze Age fig farmer, but of a burly yurt-dwelling Siberian sharing tundra turf with herds of still-extant mammoths.…
So who, indeed, is a Q? While research is still ongoing, it is possible that Qs are descended from the Khazars, the mysterious Central Asian nation that converted to Judaism 1,200 years ago. Haplogroup Q would become one of the founding lineages of Ashkenazi Jewry, which emerged 1,000 years ago. So while several of these Ashkenazi lineages, such as Haplogroup J, link to ancient Israelites, mine does not.…
Of course the other theory Silber does not mention, probably becuase he does not know about it, is that Jewish Qs are in part descended from slaves owned by early Ashkenazi Jews, the slave in your grandfather's kitchen, so-to-speak.