The Telltale Sign You Didn't Allow Your Steak To Rest Long Enough - Tasting Table
Briefly

Resting a steak is an essential step in achieving a succulent and flavorful dish. Chef Adrianne Calvo emphasizes that if juice runs from the steak upon cutting, it indicates insufficient resting time. Resting allows the meat to relax and reabsorb lost liquids, leading to better moisture retention. While a rule of thumb suggests resting for five minutes per inch of thickness, factors like the initial juiciness and ambient temperature can affect this recommendation. Understanding the science of muscle fibers contracting and expelling juice during cooking shows the impact of this technique on the end result.
If there is juice pouring out of your steak when you cut it, you didn't rest it long enough.
The whole point of resting is to let your steak, or any meat, relax, which lets it reabsorb liquid into the fibers that it may have lost during cooking.
When meat is heated its muscle fibers contract. Once they contract they can no longer hold as much water, and that liquid is expelled from those fibers.
The longer you cook meat the more dry it gets, but this process can also be reversed to an extent.
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