Sardines – Identifying Little Balls in Sardines

Hard to answer concisely, because there are many variations in processing before the Sardine hits the canning retort (a sterilization pressure cooker). Recall that there are sardines "in oil" "in spring water," even in "hot sauce." Here is a video example.

Sardines are canned under both pressure and temperature in the canning retort. I believe the pressure factor has more impact in supressing what you call scum ** though temp prolly plays a factor as well.

Home brew example: I rarely find scum like formations in my pressure cooker. I do find congealed fat on cool down.. but congealed protein.. not so much.

** Not sure if the scum you are thinking of is congealed fat, or protein.

The expiration date is (as it were) a red herring. Food doesn't suddenly go off on the expiration date. Most foods are just fine well past the expiration date; it's just the the manufacturer isn't willing to guarantee it any longer.

And all bets are off if something happened to the can. It might be hard to tell if a can of sardines was compromised. It would require only a pinhole, and sardines are usually packaged with weak spots in the can.

In your case it sounds as if the can was probably fine, since fish tends to go off in ways that are really, really obvious.

It could simply be that this is a different batch of fish. The name "sardine" applies to several different species, living in a variety of environments. That will affect the flavor.

There are many other variables as well: how they were harvested, how they were stored, how they were processed. Any of these could lead to different flavors.

If you didn't like it, you should return the can to the store. They will likely give you a refund, and push the information up the chain to the manufacturer. They're usually pretty good about that: they really, really hate it when people get food poisoning from products they sell. And it's far cheaper to give refunds to the few people who complain than to fight with a lot of customers over $3 worth of canned fish.