Don't waste your cold brew, heat contributes to the process so just brew some drip. Oxidized iron isn't going to improve the taste of coffee either!
BTW, why's everyone bashing on McDonalds coffee? Ideal brew temp for drip is higher than espresso and they significantly improved product quality with their McCafe initiative a few years back. I don't take my coffee that seriously but I prefer McD's coffee to DD and Starbucks!