Sliced into Spam and found firm white chunks embedded throughout. Is that mold or something bad

have any unusual odor. However, if the spots are accompanied by a sour smell or the texture of the Spam is off, it may be wise to err on the side of caution.
In such cases, the white spots could indicate a breakdown of the fat due to spoilage rather than just solidified pork fat.
7. How Expiration Dates, Storage, and Temperature Affect Spam Quality
The expiration date on a can of Spam indicates its peak quality. While Spam can be safe to eat past this date due to its