My taxable income before deductions is 79,588, and after deductions, my taxable income is 48,242. For some reason, I am paying a 22.3% blended tax rate. Why is this?

You are correct to a point.  

You are in the 12% tax bracket.

All of the numbers in the blended tax rate come directly off of the 1040.

But the percentage as stated can be confusing.

The Blended Tax rate is:

• Tax liability (Including SE tax, capital gain and special taxes),
•  Divided by
• Taxable income (Total income minus deductions, but before credits).

(All line numbers are on form 1040).

The Blended is your 

• Total income (line 9)
• Deductions (Line 12) This is Itemized or Standard
• Taxable Income (Line 9 – Line 12)
• Blended Tax Rate (Tax Liability [below] / Taxable Income [above])
• Tax Liability (Line 16 + Line 23)

Taxes Paid (line 25d)

Credits (Line 21)

Total Tax Paid (Line 21 + Line 25d)

Refund/Due  (Line 34 or Line 37)