Should we make an active effort to perform biur

Answer

The Chochmat Adam holds that we should distribute surplus produce (enough for three meals) to others before bi'ur time. He adds that it is best to set some aside to perform bi'ur, and this is what he would do if he merits to make Aliya (see expanded answer for the entire source).

However most posekim disagree and hold that bi'ur is a mitzvah kiyumit (a mitzvah to perform if the situation necessitates it, such as giving a get or eating bread in the sukkah besides the first night) and not a mitzvah chiyuvit (obligatory mitzvah, such as eating a kezayit of bread in the sukkah on the first night).

That is, the bi'ur applies only when someone has a large stock of shemitah produce at bi'ur time, not that one should designate an amount for bi'ur.

Note that the same halachic discussion applies to the mitzvah of bi'ur chametz.

Expanded answer

The Chochmat Adam (Sha'arei Zeddek 19:3-6) maintains that one should set aside shemitah produce in order to perform the mitzvah of bi'ur:

"If one had many fruits at the time of bi'ur, he should distribute an amount for three meals to each person. It is forbidden to eat [the produce] after bi'ur for the householder whose field it is, who is wealthy, or for others who are poor.

If he cannot find those to eat it at the time of bi'ur, he should burn it in fire or throw it into the sea and destroy it. This is the opinion of the great posekim of the Rishonim [Rambam, Ra'avad, Hilchot Shemitah 7:3].

However, in extenuating circumstances or one who is poor can rely on the great posekim [Rash 9:8; Ramban Behar; Semag positive mitzvah 148] who maintain that bi'ur for shemitah produce does not involve destroying rather the intention is that it is forbidden to take possession of the fruit as one's own. Instead, one should render everything ownerless before three of his friends, and afterwards he can claim them and eat them forever."

6: "And one who Hashem has filled his hands [i.e. is financially sound] and has the ability to perform the mitzvah of bi'ur by burning, it seems to me that he should do so: several days before bi'ur time arrives, he should distribute everything to the poor and leave over a bit of every type in order to perform the mitzvah of bi'ur so he can burn it at the appropriate time. And this is what I plan to do if Hashem will give me the merit to ascend to the Holy Land: perform the mitzvot of the seventh year and its bi'ur."

Again, the majority of the posekim disagree with the Chachmat Adam, holding that the biur is a mitzvah kiyumit.

Rav Chaim Kanievsky (Shenat Hashevah, p. 391) holds that one need not make an effort to set aside bottles specifically for bi'ur since for mitzvot whose entire purpose is getting rid of the item before a certain time, there is no need to actively get rid of it at the appointed time.

This differs from bi'ur chametz for two reasons:

1. The night before, at the time of bedikat chametz , we say the berachah "al bi'ur chametz." We ensure we have chametz to burn in order to avoid a berachah levatalah.
2. Furthermore, for shemitah produce, we are supposed to eat it and avoid wasting it (hefsed)! This is not the case for chametz.

The educational aspect of bi'ur

Above, we saw that most posekim do not agree with the Chochmat Adam and hold that one need not make an effort to perform bi'ur.

Nevertheless, there is an educational aspect of this mitzvah. Rav Yehudah Amichay, head of Torah Veha'aretz Institute, holds that if you wish to perform bi'ur (via hefker), set aside a small amount, such as one bottle and render it ownerless.

In this way, even those without large stocks of shemitah produce can remember the mitzvah of bi'ur.

This is our chance to connect to the feeling farmers have when having to render all of their crops ownerless last year, in instill within us the notion that everything belongs to Hashem, and not to us.

Note: The amount of wine or grape juice needed for Seder night for family members and guests is exempt from bi'ur.