After pouring that satistying drizzle of mirror glaze, you should have a lot left over. If you store it properly, it will last for months to reuse again and again. Just remember two important details:
Leftover mirror glaze can be frozen without issue, but there is no need as long as you lock in all of the moisture and store it in your refrigerator. No mold will grow and the flavors will be locked in.
For this task, a vacuum sealer is the best tool. Simply let your glaze drizzle into the vacuum bag, cool until gel, then vacuum and seal twice.
If you don't have a vacuum-sealer, you can use a manual zipper bag. The exposure to the air inside the bag and imperfect seal will dehydrate the mirror glaze, make the flavors stale, and permit mold to grow. Because mirror glaze is almost always prepared in bulk, you will be throwing out otherwise good product. For this reason, a vacuum sealer is a worthwhile investment, useful for virtually every food—sweet or savory—you plan to store for more than a few days.
If you go the route of zipper bags, be sure to press out as much air as possible and triple-bag it to extend the lifetime.
When ready to use again, cut open the vacuum-sealed bag. You now have to reheat the mirror glaze to 94°F (34°C), which you can either do over the stove or in the microwave. Since mirror glaze does not conduct heat well, you must break up the gel chunks as much as possible and keep it stirring in motion. The more you stir, the more even the heating. You will quickly get to the right temperature without burning.
Use an immersion blender to process the glaze until smooth, just as you did in preparing the glaze.
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