Maurice Lamm, The Jewish Way in Death and Mourning (1969)
Cremation is never permitted. The deceased must be interred, bodily, in the earth. It is forbidden - in every and any circumstance - to reduce the dead to ash in a crematorium. It is an offensive act, for it does violence to the spirt and letter of Jewish law, which never, in the long past, sanctioned the ancient pagan practice of burning on the pyre...Even if the deceased willed cremation, their wishes must be ignored in order to observe the will of God. Biblical law takes precedence over the instructions of the deceased...Cremated ashes may not be buried in a Jewish cemetery... Shivah is not observed and Kaddish is not recited for them...
Cremation is never permitted. The deceased must be interred, bodily, in the earth. It is forbidden - in every and any circumstance - to reduce the dead to ash in a crematorium. It is an offensive act, for it does violence to the spirt and letter of Jewish law, which never, in the long past, sanctioned the ancient pagan practice of burning on the pyre...Even if the deceased willed cremation, their wishes must be ignored in order to observe the will of God. Biblical law takes precedence over the instructions of the deceased...Cremated ashes may not be buried in a Jewish cemetery... Shivah is not observed and Kaddish is not recited for them...
כי קללת אלהים תלוי הנה כל עצם נבדל מחומר יקרא אלהים ומזה המין הוא עצם הנפש השכלית באדם הנקראת צלם אלהים. וע''ז הדרך אמרה בעלת אוב לשאול אלהים ראיתי עולים. ובהיות שהבזיון הנעשה למת אחר מיתה הוא בזיון לנפש השכלית אשר היא עצם נבדל הנשאר אחר מיתת הגוף אמר שהוא קללת אלהים כי הלנת חתליה לגוף המת בלתי קבורה היא בזיון לאותו העצם הנצחי הנקרא אלהים:
כי קללת אלוהים תלוי, every disembodied creature is known as elohim; this includes the soul of human beings known as צלם אלוהים, “image of G’d.” [as He is without body, so this essence of a human being is without a body, does not need a body. Ed.] (Genesis 1,27) This is how we can understand the woman, known as בעלת אוב in Samuel I 28,13 whom King Sha-ul approached and asked to raise the prophet Samuel for him producing a disembodied image. Seeing that the disgrace done to a person after he has died is also an insult to this disembodied essence of him, the Torah describes it as קללת אלוהים, equivalent to cursing the dead person’s eternal essence. קללת אלהים, leaving the dead corpse hanging without burial is an insult to that very eternal essence of a human being called אלהים.
From "Judaism and the Human Body" by Rabbi Bradley Artson
For that same reason, Jewish tradition prohibits cremation as undignified to the body of the deceased, and Talmudic tradition affirms a physical resurrection of the dead. One need not share every Talmudic belief about the afterlife to recognize great wisdom in preserving a sense of awe and gratitude for the human body.
In an age awash in self-destructive drugs, too busy to exercise or to eat carefully, respect for our bodies is dangerously low on our agenda. Teenagers and women smoke in growing numbers, and alcohol use, too, is on the rise. Biblical and Rabbinic tradition maintain that our bodies reflect God’s image and therefore command respectful maintenance. In addition, our bodies are not our property, but God’s. We use them, as the tenants and stewards of God’s possessions. But ultimately, our bodies must be returned, well-tended, to their original Owner.
For that same reason, Jewish tradition prohibits cremation as undignified to the body of the deceased, and Talmudic tradition affirms a physical resurrection of the dead. One need not share every Talmudic belief about the afterlife to recognize great wisdom in preserving a sense of awe and gratitude for the human body.
In an age awash in self-destructive drugs, too busy to exercise or to eat carefully, respect for our bodies is dangerously low on our agenda. Teenagers and women smoke in growing numbers, and alcohol use, too, is on the rise. Biblical and Rabbinic tradition maintain that our bodies reflect God’s image and therefore command respectful maintenance. In addition, our bodies are not our property, but God’s. We use them, as the tenants and stewards of God’s possessions. But ultimately, our bodies must be returned, well-tended, to their original Owner.
מִנְּהַג יִשְׂרָאֵל בְּמֵתִים וּבִקְבוּרָה כָּךְ הוּא. מְאַמְּצִין עֵינָיו שֶׁל מֵת. וְאִם נִפְתַּח פִּיו קוֹשְׁרִין אֶת לְחָיָיו. וּפוֹקְקִין אֶת נְקָבָיו אַחַר שֶׁמְּדִיחִין אוֹתוֹ. וְסָכִין אוֹתוֹ בְּמִינֵי בְּשָׂמִים. וְגוֹזְזִין שְׂעָרוֹ. וּמַלְבִּישִׁין אוֹתוֹ תַּכְרִיכִין תְּפוּרִין בְּחוּט שֶׁל פִּשְׁתָּן לְבָנִים. וְלֹא יִהְיוּ דְּמֵיהֶן יְקָרִים. וְנָהֲגוּ חֲכָמִים בְּסוּדָר שְׁוֵה זוּז שֶׁלֹּא לְבַיֵּשׁ אֶת מִי שֶׁאֵין לוֹ. וּמְכַסִּין פְּנֵי הַמֵּת שֶׁלֹּא לְבַיֵּשׁ אֶת הָעֲנִיִּים שֶׁפְּנֵיהֶם מֻשְׁחָרִין בָּרָעָב:
These are the customs observed by the Jewish people with regard to corpses and burial. We close the eyes of the deceased. If one's mouth hangs open, we tie the jaw closed. After washing the corpse, we stuff closed the orifices, anoint it with different fragrances, cut its hair, and dress it in shrouds of white linen which are not expensive. Our Sages followed the custom of using a cloak worth a zuz, so as not to embarrass a person who lacks resources. We cover the faces of the deceased so as not to embarrass the poor whose faces turned black because of hunger.
הַהֶסְפֵּד כְּבוֹד הַמֵּת הוּא. לְפִיכָךְ כּוֹפִין אֶת הַיּוֹרְשִׁין לִתֵּן שְׂכַר מְקוֹנְנִים וְהַמְקוֹנְנוֹת וְסוֹפְדִין אוֹתוֹ. וְאִם צִוָּה שֶׁלֹּא יִסְפְּדוּהוּ אֵין סוֹפְדִין אוֹתוֹ. אֲבָל אִם צִוָּה שֶׁלֹּא יִקָּבֵר אֵין שׁוֹמְעִין לוֹ. שֶׁהַקְּבוּרָה מִצְוָה שֶׁנֶּאֱמַר (דברים כא כג) "כִּי קָבוֹר תִּקְבְּרֶנּוּ":
Funeral rites are held in honor of the deceased. Accordingly, the heirs are compelled to pay a fee to wailing men and women who eulogize the dead. But if the deceased charged in his will not to eulogize him, he should not be eulogized. If, however, he charged in his will not to bury him, his wish is not heeded, because burying the dead is a religious duty, as it is written: "You must bury him" (Deuteronomy 21:23).
Is Human Composting Permitted in Judaism? by Yehuda Sherpin
Since you ask about human composting as an eco-friendly alternative, it should be noted that, broadly speaking, Jewish burial practices are already environmentally friendly.
In Jewish burial, the body is carefully cleansed with water, wrapped in a simple linen shroud, and placed in an unadorned wooden casket (in Israel they don't even use a casket). It is then buried in the earth, where decomposition happens naturally in a matter of months. Ornate caskets with non-biodegradable materials and chemical-based embalming are not in line with traditional Jewish burial customs.
Human composting is designed to use human remains as compost to foster growth. Some go as far as to plant a tree using the composted remains.
However, this directly conflicts with Judaism’s stance on the sanctity of the body, even in death. One is biblically prohibited from benefiting from any part of the deceased body, as well as the shrouds and other burial items accompanying it.
Consequently, intentionally composting a body for utilitarian purposes is prohibited according to Jewish law.
Since you ask about human composting as an eco-friendly alternative, it should be noted that, broadly speaking, Jewish burial practices are already environmentally friendly.
In Jewish burial, the body is carefully cleansed with water, wrapped in a simple linen shroud, and placed in an unadorned wooden casket (in Israel they don't even use a casket). It is then buried in the earth, where decomposition happens naturally in a matter of months. Ornate caskets with non-biodegradable materials and chemical-based embalming are not in line with traditional Jewish burial customs.
Human composting is designed to use human remains as compost to foster growth. Some go as far as to plant a tree using the composted remains.
However, this directly conflicts with Judaism’s stance on the sanctity of the body, even in death. One is biblically prohibited from benefiting from any part of the deceased body, as well as the shrouds and other burial items accompanying it.
Consequently, intentionally composting a body for utilitarian purposes is prohibited according to Jewish law.