A.) There are two issues about these casings: the first issue is whether it can be held as pure (Ta’hir). After studying the processes it is quite clear that the hides used for production of these casings become pure after passing through the process which includes lime treatment for 4/5 days. The principle of Shariah is that the hide of an animal, even not slaughtered in the Islamic way, is purified by the process of Dabaghah (tanning).
This principle is agreed upon by all the juristic schools of the Muslims. Therefore, if these casings are used merely to preserve the contents of halal beef in a particular shape but the consumer eats it after removing the casing, it is halal without any doubt.
The second issue is whether it is halal to eat the casing itself. The answer to this question is that according to the majority view of the Muslim jurists it is not permissible to eat the hide of an un-slaughtered animal even after tanning. However, a large number of Sha’fie jurists as well as a small number of Hanafi jurists have allowed to eat it after tanning. But this minority view could not find favor with the latter day fuqaha who are of the firm opinion that it is not permissible for oral use and therefore the minority view should not be followed.
One may argue that the process mentioned in your question transforms the hide into something else and therefore it should be declared a new product having no prohibited element. But this argument does not seem to be correct because the Collagen is a form of protein which is the major ingredient and it remains unchanged; merely the change of shape or the process of purification does not seem to transform the nature of the hide.
The net result in brief is that the casing made of an un-slaughtered animal’s hide after the process becomes pure and does not affect the beef content in it. If a Muslim uses the food content in such a casing after scrapping the casing it is permissible for him to eat but it is not permissible to eat the beef with its casing. Since it is difficult for a producer to control the consumers in this respect it seems necessary that he must acquire casings produced by the hides of slaughtered animals. This is my personal opinion. It will be advisable to consult other Ulama also.
By Mufti Taqi Usmani