It is proper to partake of meat and wine on the holiday of Rosh Hashanah. Instinctively, one might have assumed that meat and wine are inappropriate on this holiday, when we stand in judgment before God; if anything, we might have thought, on such on occasion we should be eating stale bread and drinking water. In truth, however, Halacha requires partaking of meat and wine on Rosh Hashanah to express our confidence in the favorable judgment that we will earn. It goes without saying, though, that this day is most certainly not a time for gluttonous indulgence and frivolity. The proper way to conduct oneself is expressed in the famous verse in Tehillim (2:11), "Ve’gilu Bi’r’ada" ("…and rejoice with trembling"); meaning, our joyous celebration must be combined with a sense of awe and reverence.
There are a number of foods which people customarily refrain from eating on Rosh Hashanah. For example, the Rama (Rabbi Moshe Isserles, Poland, 1525-1572) records a custom not to eat "Egozim," walnuts, on Rosh Hashanah, because the word "Egoz" has the same numerical value (17) as the Hebrew word "Het" (sin). (This assumes that the word "Het" is spelled without the letter "Alef"; normally, however, we indeed do spell "Het" with an "Alef.") In order to avoid even subtle allusions to sin on Rosh Hashanah, many people have the practice to avoid walnuts on this holiday. Others have the custom to refrain from nuts altogether on Rosh Hashanah, because nuts tend to cause mucous in one’s throat, and the noise of people clearing their throats in the synagogue might drown out the sounds of the prayers and the Shofar blowing.
There is another custom to refrain from all sour and bitter foods on Rosh Hashanah, such as lemons, vinegar and raw garlic. On Rosh Hashanah we seek omens for a sweet, pleasant year, and therefore many people refrain from sour and bitter foods.
Furthermore, some people follow the custom not to eat fish on Rosh Hashanah, due to the similarity between the words "Dag" ("fish") and "De’aga" ("worry"). We look forward to a year free of anxiety and stress, and thus we do not wish to make any reference to "De’aga" on Rosh Hashanah. However, the Kaf Ha’haim (work by Rabbi Yaakov Sofer, Baghdad-Israel, 1870-1939) writes in the name of Rav Haim Palachi (Turkey, 1788-1869) that when Rosh Hashanah falls on Shabbat, one should eat fish on that day. Our Rabbis emphasized the importance of eating fish on Shabbat, noting, "Whoever eats ‘Dag’ on the day of ‘Dag’ is saved from ‘Dag’." This means that one who partakes of "Dag" (fish) on the seventh day (the word "Dag" has the numerical value of seven), Shabbat, is saved from "Din Gehinam" – the punishments of Gehinam. Therefore, although there is a custom to refrain from fish on Rosh Hashanah, one should eat fish when Rosh Hashanah falls on Shabbat.
Finally, Kabbalistic tradition teaches that one should refrain from eating black grapes on Rosh Hashanah, whereas it is advisable to eat white grapes on Rosh Hashanah.
Summary: There is a Misva to partake of meat and wine on Rosh Hashanah. Different customs exist concerning the consumption of certain foods on Rosh Hashanah. Some have the custom not to eat walnuts, and others refrain from nuts altogether. There are those who do not eat any sour or bitter foods on Rosh Hashanah. Another custom advises refraining from fish on Rosh Hashanah, though even adherents of this practice should eat fish when Rosh Hashanah falls on Shabbat. Black grapes should not be eaten on Rosh Hashanah, but white grapes may be eaten.
