Not a week goes by without a customer leaning over the meat case and asking for porterhouse steaks. We LOVE this question (except during busy rushes) because it is an excellent entry point into many of the things that we care about as students of old-world butchery: pasture raised meat and how it should be treated, optimal cooking for every part of the animal, and the dry-aging process.
Let's begin with understanding what a porterhouse is. Anatomically speaking, a porterhouse is comprised of two distinct cuts: the tenderloin to one side and the NY Strip or short loin to the other (See Exhibit A). The "T" shaped bone separating the two is the result of the vertibra of the steer being cut down the middle. (Hence the term 'T-Bone' steak, which is just like a porterhouse but with a smaller portion of tenderloin.) Individually, these two steaks are amongst the most valuable and rare of the whole animal (See Exhibit B).
Certainly combined their magnificance must be unbeatable, right? This is where we beg to disagree.
To begin with, the strip loin and the tenderloin cook at different rates, pure and simple. When grilling or pan searing your porterhouse, the tenderloin will be ready to go before the NY Strip 99% of the time. If you're going to plunk down $25+ per pound on a steak, you certainly want all parts of it to be perfectly cooked.
The case against porterhouses gets stronger upon closer inspection of the delicate, flavor-enhancing dry aging process. Dry aging is a costly storage process reserved for the most evenly marbled cuts of beef, namely the rib and loin sections. Over the course of 3-4 weeks, our Rib Eyes and NY Strips are stored just above freezing in our walk in with ample airflow all around them. Letting the meat rest increases tenderness and allows natural enzymes in the beef to break down connective tissue. Furthermore, evaporative weight loss (of up to 18%!) concentrates flavor.
Dry aging almost completely disappeared in the US due to associated costs and the significantly increased risk of unwanted microbial growth in industrially raised meat. For a long time, most beef in the US was 'wet aged': cut immediately into primals, vacuum sealed in plastic and shipped to butcher shops around the country. The meat does become more tender in the bags, but little concentration of flavor takes place. Recently, 'gas packing' has risen to prominence. Enhancing neither flavor nor tenderness, this process packages meat with carbon monoxide to keep it looking red so it can stay on shelves longer. But we digress.
Long story short, tenderloin is extremely lean and therefore suffers when dry-aged. Strip loin, on the otherhand, benefits tremendously from the process and would be rather tough without it. An that, dear customers, is why we just can't sell you porterhouses with a clear conscience. We rest our case.