Purchased some 8 oz NY Strip Steaks yesterday afternoon from the fresh meat case at a local grocery store. They were priced per steak, not by individual piece weight. When I got them home I weighed them on a scale I trust and every one was less than 7.3 oz. A couple weighed in at 6.7 oz. Based on the color and moist appearance they looked as if they were pretty freshly cut. I talked with the Meat Dept manager and he said that they are allowed some variance for shrinkage and also that it is nearly impossible to cut them exact. I understand that meat starts to dehydrate when it is cut and also about the difficulty cutting them exactly 8 oz. He did apologize and offered to cut some fresh ones for me. My question is how much shrinkage should be expected before they are ever cooked? What's reasonable?
OK, from a technical perspective, a couple things come to mind here: by weighing on a scale you trust doesn't mean it's accurate, unless you have proven it to be accurate...and for the general population, there are no perfect ways to verify scale accuracy, unless you KNOW the weight of a measuring cup and fill it with water, then calculate the actual water weight (not the measure by volume) and determine if it is in fact accurate. Knowing the exact weight of your water is not possible without a hydrometer to measure the specific gravity, as water weight (SG) changes with mineral content, fluctuates from one area to another, and, can change to some degree in a given specific area/location. Using water is just one of many ways to determine scale accuracy without having a weight kit, but to my knowledge it has the lowest risk for error if used correctly. I have a postal-grade 30lb digital scale that measures in 0.2oz increments, and claims an accuracy to within 0.2oz...I haven't checked it to verify it's accuracy for a couple years now, due to not needing a high degree of accuracy as I have not done any meat curing lately...so, that said, I have no reason to trust my scale. Retailer's scales are verified periodically by acceptable and trusted methods. I rarely get a scale reading that is the same as the retail packaging states, even with the tare weight for a total...I usually show less on my scale...I doubt that everywhere we purchase meat from would get away with it for very long if their scales were off as much as you described. Sure there is a small allowance for scale error, but you're speaking of somewhere in the range of -16.25%...that would be a rather serious violation of trade standards and would not be worth the risk to any retailer to have scales that far out of tolerance.
Variance for shrinkage in meats: it will shrink little to none while wet aging in the retail package, and what little bit it might if it did is caused from moisture loss...the moisture should (better) still be in the package...I think we can agree on this, correct? So, for retail purposes, they should err on the side of the consumer...too heavy, not too light, when packaged for sale as a stated, but not actually verified, weight.
As for losses from cooking, there is always some loss of water weight due to cooking...it's just part of the process. How much loss you should expect to see will depend on 1) the finished internal temp after resting, 2) fat content and amount of rendered fat after cooking [fat has less water than muscle, but more fat loss and water loss will occur with higher fat content] 3) method of cooking, 4) ambient humidity, and more importantly 5) the cooker's humidity, and 6) resting time and method of resting prior to serving. Cooking to lower I/T equals less water evaporation, but the other factors will change the final water loss to a smaller degree, yet each of these will effect it in varying amounts. Because I haven't weighed cooked steaks to compare to precooked weights (never had a reason to in the past) I can only speculate on water weight loss...possibly 7-8% for med-rare, as a baseline, for example, and probably closer to 20% for med-well...these I would estimate for char-grilled...open grate smoking low & slow (225*) with low humidity, and even with reverse sear, probably less loss would occur. Braised or steamed would likely suffer higher overall losses.
All that said, my best advice is to buy in larger packages and portion it to the amount you want to cook for freezing after repackaging...preferably in vac-sealed bags. I never buy single small cuts, due to price gouging alone, as you're paying more for extra labor to process more packages for the smaller portions. If something is a "manager's special" or "reduced for quick sale" it has very little time left before needing to be frozen or cooked, and as a result, allows less for thaw to cooking time before the risk of illness rises beyond measure. Lastly, steer clear of pre-seasoned meats...that's typically just a cover for meats about to go bad...meat dept mangers don't want to lose the sale of any meats and at times are forced to drastic measures to keep their profit/loss margins looking good on paper...the dreaded "keep the profits up or find another job". Unethical store owners? You bet!!! Would I trust stores who I have seen using these practices with all of my potential purchases? Not a chance...(trust is earned...it's not a right and it's not permanent). Illegal? Possibly...I don't have the time or desire to research it at the moment and have not yet read about it anywhere...
Eric