Siman 489, Se'if 10

Shulchan Aruch, siman 489, se'if 10
"It is forbidden to eat chadash (new grain) even nowadays, whether as bread, roasted kernels (kali), or fresh kernels (karmel), until the beginning of the night of the eighteenth of Nissan; and in Eretz Yisrael, until the beginning of the night of the seventeenth of Nissan."
(Shulchan Aruch)

Where this halacha belongs, and why it appears here

The main discussion is in Yoreh De'ah: The laws of chadash, new grain, are treated primarily in Yoreh De'ah, where all the details are laid out at length. The Shulchan Aruch chose to mention the halacha here as well, briefly, among the laws of Pesach, because the time when the new grain becomes permitted depends on the days of Pesach.

Defining "chadash" and when it becomes permitted

"That is, grain that took root after the sixteenth of Nissan, which is the time the Omer offering is brought."
(Mishnah Berurah, s.k. 44)

When the Beis Hamikdash stands: The Omer is waved on the morning of the sixteenth of Nissan, and from the moment it is waved the new grain is permitted to all of Israel.
Nowadays: Since there is no waving of the Omer, the entire day of the sixteenth of Nissan remains forbidden for chadash. Once the sun sets and the stars come out, and the night of the seventeenth of Nissan begins, chadash is permitted in Eretz Yisrael.
The decree of Rabban Yochanan ben Zakkai: From the verse itself there would have been room to permit chadash at midday of the sixteenth, but Rabban Yochanan ben Zakkai decreed that the whole day should remain forbidden.

The time it takes to take root, and what this means in practice

How long rooting takes: Some say three days, that being the time in which the seed is absorbed into the ground and takes root.
The practical difference: Grain sown three days before the sixteenth of Nissan is considered grain that this year's Omer permits. Grain sown one day before the sixteenth of Nissan, which has not yet been absorbed into the ground, has the status of grain sown afterward, and one must wait until the sixteenth of Nissan of the following year has passed.
The situation in Eretz Yisrael: In Eretz Yisrael there is no summer grain; everything is sown in the winter, so the sixteenth of Nissan always passes over it and there is no problem of chadash.

The five species of grain to which the prohibition applies

The species: The prohibition of chadash applies only to the five grains: wheat, barley, spelt, oats and rye.
Kussemin, not kussemes: Kussemin (spelt) is a particular variety of wheat and is one of the five species. Kussemes (buckwheat) is an entirely different plant, comparable to rice; it is not among the five species and the prohibition of chadash does not apply to it. People tend to confuse the two names.

Bread, kali and karmel: the forbidden forms of eating

Bread: If new grain was baked, the bread is forbidden to eat.
Kali: Kernels roasted over fire are likewise included in the prohibition.
Karmel according to Rashi: Rashi explains "karmel" from the words "rach u'mal," soft enough that the kernels can be crushed by hand. According to this, even wheat kernels just as they are are forbidden under the prohibition of chadash.

(The definition of "karmel" is the subject of much discussion, so one should not decide it simply.)

Questions about common products

Oatmeal (Quaker): Generally made from oats. Based on an investigation of the manufacturing process, which involves cooking followed by heating, the conclusion is that it falls under the prohibition of chadash, and one has to look into the details of production.
"Shalva" (a children's snack): Made from wheat kernels that pop when heated. There is room to say it is included in "karmel," and room to say it is included in "kali," since the heating is a form of roasting. One cannot decide the matter, because of the dispute over the definition of karmel. The berachah on it is borei pri ha'adamah, but the berachah is not what determines the issue here.
Popcorn: Made from corn, which is not one of the five grains, and there is no prohibition of chadash in it.
Grain-based beverages (beer): This question was left open; the discussion here concerns solids.

"Even nowadays," and in every place

The source of the prohibition nowadays: From the verse "And bread, kali and karmel you shall not eat until this very day," and from the words "until this very day" they derived that the day itself permits, even when there is no offering.
Two expressions in the Torah: On the one hand the verse says "until you bring the offering of your God," and on the other hand "until this very day." From here Chazal derived two situations: when the offering can be brought, the bringing of the offering permits; when it cannot be brought, the day permits, that is, once the entire day of the sixteenth of Nissan has passed.
"In all your dwelling places": From here we learn that the prohibition applies wherever Jews dwell, including outside Eretz Yisrael.
The doubt about the date outside Eretz Yisrael: Outside Eretz Yisrael, where the second day of Yom Tov adds a day, we are stringent for one additional day, and therefore chadash becomes permitted there only on the night of the eighteenth of Nissan.

Is this a mitzvah dependent on the Land?

The basic distinction: The Omer offering itself is dependent on the Land, for the barley brought to the Beis Hamikdash may come only from what grew in Eretz Yisrael, and it cannot be brought from outside the Land.
The permitting effect: Nevertheless, the effect of the offering is not limited to the Land. It permits grain outside the Land as well, and the two matters are not linked.
The example from the offerings: The regular offerings in the Beis Hamikdash, the morning tamid and the afternoon tamid, are brought in the Land, and yet their effect is upon all of Israel, including those living outside the Land.

The Rema's leniency for chadash outside Eretz Yisrael

The background reality: The Rema lived outside Eretz Yisrael, where much of the produce is summer produce, since rain falls there in the summer as well. The grain is harvested and reaches the market in the summer and autumn months, when the time of the Omer is very far off, so that there would be no possibility of eating grain products for a long stretch of time.
The severity of the difficulty: In Eretz Yisrael this is not much of a problem, since everything is winter grain, but outside the Land it was a serious hardship, and so the great authorities of the generations sought grounds for leniency.
Where the halacha is found: The Rema wrote his leniency for chadash in Yoreh De'ah, and the Mishnah Berurah brings his words here.

The leniency based on a sfek sfeika (double doubt)

"For it is a double doubt: first, perhaps the grain is from last year; and even if you say it is from this year, perhaps it took root before the Omer."
(Mishnah Berurah)

The first doubt: We do not know the source of the grain brought to market, and it may be from last year and have been sitting in storage.
The second doubt: And even if it is from this year, it may have been sown and taken root before the Omer, since the spring season does not begin precisely at Pesach, and in a warm year people sow earlier.
The same applies with imports: In a place to which grain is brought from elsewhere, where the grain took root before the Omer, the same double doubt applies.

The limitation of the later authorities in Poland

"And in the country of Poland one may be lenient only with wheat and rye, since the vast majority are sown in the month of Cheshvan."
(Mishnah Berurah)

Wheat and rye: Since the agricultural practice there is to sow them in Cheshvan, there is no prohibition of chadash in them, apart from those known to have been sown in the summer.
Barley, oats and spelt: Most of them, virtually all of them, are sown there after Pesach, so there is no doubt at all but clear knowledge that the grain is new, and one must wait until the following year.
No imports: Nor is it common there to bring grain from other countries, so the second doubt is absent and there is no double doubt.

Most of the world is not careful; on what do they rely?

The reality: Even in places where it is clear that the grain is new, most of the world is not careful about the prohibition of chadash at all.
A defense of their practice: Some have defended them, on the grounds that it is a hard thing to be careful about.
The weakness of that defense: Difficulty in itself does not permit something, for other mitzvos are also hard to keep and that is no license.
The basis of the leniency: Rather, under pressing circumstances people rely on some of the Rishonim who hold that the prohibition of chadash outside Eretz Yisrael is only mid'divrei sofrim, rabbinic. This is not a dispute about the words of the Gemara itself, since there is an explicit Mishnah that the prohibition applies outside the Land as well; it is a dispute about how to understand the Gemara and the scope of the prohibition, that is, upon what the prohibition falls: some say it falls only on what grew in the Land and not on what grew outside it.

(The continued explanation of the positions of the Rishonim regarding chadash outside Eretz Yisrael will be explained further on.)

Those who were stringent about chadash

The great stringent authorities: The leniency was not adopted lightly, and there was considerable opposition to it. The most famous of those who were stringent is the Gra (the Vilna Gaon), and so too the author of the Sha'agas Aryeh, and there were other great authorities who were very stringent in this matter.
How far the stringency went: It is told of the Gra and of the author of the Sha'agas Aryeh that when they wandered in exile they carried their own utensils with them, and would not eat from their hosts' utensils, even though those hosts kept kashrus and received them with honor, because Jews outside Eretz Yisrael were lenient about chadash and cooked chadash in their vessels.

In passing · Torah she'be'al peh as the foundation of interpretation

A question was asked: why does the prohibition of chadash apply outside Eretz Yisrael, when the verse says "in all your dwelling places," and "your dwelling places" means the Land promised to Israel? The answer to this is a fundamental principle in how we learn.

One does not read a verse without the Oral Torah: Halacha cannot be derived from one's own reading of a verse. A proper question arises only out of studying the sugya in the words of Chazal, and here there is an explicit Mishnah that the prohibition of chadash applies outside the Land as well.
The example of the "beautiful fruit": The Torah says "And you shall take for yourselves on the first day the fruit of a beautiful tree," and there is no esrog written there. Without the Oral Torah, anyone could take a lemon, an orange or a grapefruit, and there is no way to arrive at an esrog.
The transmission of the Oral Torah: "Moshe received the Torah from Sinai and transmitted it to Yehoshua, Yehoshua to the Elders, the Elders to the Prophets." The transmission is not the handing over of a book, for the book sits in the Aron; it is the transmission of the Oral Torah, and without it one cannot move a step.
The Rambam's introduction: The Rambam opened the Mishneh Torah by listing the chain of generations, who received from whom down to the Geonim, to show that the interpretation by which we explain the Torah is not the innovation of one man but a tradition from Moshe Rabbeinu. Without that, the book has no value.
The Karaites: The Karaites interpreted the Torah in their own way, and Klal Yisrael cannot accept such an interpretation, since it has no authoritative tradition behind it.
Disputes in details, not in fundamentals: No one disputes that we recite Krias Shema twice a day; the dispute is over the details, how many parshiyos. No one disputes the identity of the esrog, the lulav, the hadassim and the aravos, though there could be a dispute whether one takes three hadassim or two, since the verse says "a branch of a leafy tree" in the singular.
A further example: "On the morrow of the Shabbos" regarding Sefiras HaOmer. By the plain meaning of the words there would be room to begin counting on Sunday, yet we begin at the conclusion of the first day of Yom Tov of Pesach, because it is the Oral Torah that explains what that "Shabbos" is.

In passing · The practice of "galus" among the great of Israel

What they did: There were great men of Israel who left their home city and wandered in exile for a year, two, or three, and then returned to their city.
The reason: They took exile upon themselves, because exile atones for sins, even for sins a person is not aware of.
What is told of the Gra: He was asked why he took exile upon himself, since from the age of four or five he was immersed in Torah, and he answered that he was doing so because when he nursed from his mother he used to pinch her.

In passing · Importing grain into Eretz Yisrael today

The problem: Although in Eretz Yisrael itself everything is winter grain and there is no concern of chadash, today a great deal of grain is imported into the Land from abroad, so the question exists in Eretz Yisrael as well. The details of the halacha in this will be explained further on.