  Over a complete Noetherian local domain of mixed characteristic with perfect
residue field, we construct a perfectoid ring which is similar to an explicit
representation of a perfect closure in positive characteristic. Then we
demonstrate that this perfectoid ring is almost Cohen-Macaulay in the sense of
almost ring theory. The proof of this result uses Andr\'e's flatness lemma
along with Riemann's extension theorem. We stress that the idea partially
originates from the ``perfectoidization" in the theory of prismatic cohomology.
