We all know that you’re not supposed to re-freeze meat, because every time you thaw and re-freeze it tends to dry out.
BUT… what about liquid? I’ve been a stock-making fool this past month, and I have something like 40 quarts of stock in the freezer. If I take one out, thaw it, and only use half of it, what will happen if I re-freeze the remainder? How can liquid dry out?
It’s not just that meat tends to dry out - it’s that bacteria have a chance to multiply while it’s thawed, so every time you thaw & refreeze, you wind up with more bacteria in the meat.
The same is probably true for stock - room temperature stock is a wonderful medium for bacteria to grow in - but it has the advantage that you can boil it before use. So WAG, as long as you boil the refrozen stock before use, you’re good to go. FWIW, Alton Brown recommends boiling all frozen stock for 2 minutes before use.
It won’t dry out, but if you repeatedly thaw and freeze something that can spoil (like chicken or beef stock) you allow it to repeatedly cross into a warm enough temperature range in which bacteria can grow more rapidly.
The same thing happens with any other food product, including meat. For meat, however, in addition to this, the freezing process causes ice crystals to rupture cells, which results in the meat drying out.
Freezing only works as long-term storage because it virtually halts the proliferation of bacteria. Any rise in temperature, however, allows bacteria the ability to resume their growth. In short, it’s best not to thaw and refreeze anything that can spoil.