Can someone provide me with some details and background about Rabbi David I. Sheinkop? He's involved in kashrus hashgacha and after reading his short sefer on gelatin, he appears to me to be very knowledgeable as well as a person who bases his decisions on traditional Halachic sources. Is he accepted by the main stream of Orthodox Jews as someone who can be relied on?
Regarding Gelatin, this is what he says (YMMV). The hecsherim that he gives would follow his view on this matter. Other hechsherim could differ and your determination to accept him or not should be based on you rav's opinion of this matter.
GELATIN IN JEWISH LAW By Rabbi David I. Sheinkopf
Gelatin produced from cattle bones or hides of even non-ritually slaughtered animals is kosher in full accordance with orthodox Jewish dietary laws. The reason is that only the edible parts of non-kosher animals are forbidden. Bones and hides, however, which are inedible, are excluded by the Talmud and Jewish Law Codes from any category of foodstuffs. Therefore, after undergoing chemical pretreatments which render them absolutely free of any forbidden extraneous materials, bones and hides in themselves are permissible.
Soaked in hydrochloric acid and/or lime for extended periods of time, the raw material is reduced to pure collagen with no traces of adhering flesh, marrow, or grease whatsoever. (Those who contend otherwise are simply unfamiliar with the manufacturing process.) Hence, the gelatin extracted from the collagenous residue of bones and hides is kosher. This is true regardless of whether gelatin is considered a new substance (davar hadash). Also, because it originates from a non-edible substance, gelatin is pareve (neither meat nor dairy.)