Can I ruin a 1.039 beer using 2 sachets of yeast instead of 1?

I am pretty sure I cant....but I'd like to know what you guys think?

I have US-05 yeast sachets from last year....and the mrmalty calculator says that even so, I only need 1.1 sachet of yeast.
I'll rehydrate 2 sachets and pitch with those. Can it affect the beer in any ways?

 

I'm sure you'll be fine. If you pitch twice what Mr. Malty says to pitch (or 1.5 million cells/ml/°P), you still get more than a full doubling during fermentation and you are effectively pitching at lager rates. If the packets were at room temperature for a year, they may have viability of around 50% (it loses roughly 4% viability per month at room temp, vs 4% per year at fridge temp). I wouldn't worry about it. FWIW, though, it's probably unnecessary to pitch that much into a 1.039 beer if you've been keeping the packs refrigerated.

 

the issue of over pitching is you often lose out of the flavors that the yeast provide to the beer. Since you're pitching US05 (a clean fermenting yeast) I think you'll be fine even if you're over pitching regardless of its age.

 

To be fair, there are other issues associated with a major overpitch, but you'd have to pitch a lot more before you worry about those (yeast health, beer quality, etc.).

Snippet from BYO:

Again, though, you are no where even in the ballpark of having to worry about off flavors as a result of overpitching with 2 packs of 05 assuming you are doing somewhere around 5 gallons.