What is the effect of the Court of Appeal's failure to provide a standard burden of proof instruction such as CALJIC 2.90?

[7] When the trial court instructs the jury, at a minimum, that the prosecution must prove its case beyond a reasonable doubt and the definition of that standard is appropriate, then failure to give the standard burden of proof instruction such as CALJIC 2.90, is not per se reversible error. ( People v. Flores (2007) 147 Cal.App.4th 199, 211, 54 Cal.Rptr.3d 98 ( Flores ).) Rather, we review the record to determine if the error was " harmless beyond a reasonable doubt." ( Chapman v. California (1967) 386 U.S. 18, 24, 87 S.Ct. 824, 17 L.Ed.2d 705 ( Chapman ).) To determine whether the error in this particular case warrants reversal, it is instructive to evaluate the pretrial instructions and the predeliberation instructions as to each substantive charge.