50/50 lye solution question

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You are talking about dried-up lye solution on the rim; that is a different issue than precipitation, and it doesn't affect the strength of the remaining solution. To prevent the buildup, wipe the pouring edge completely dry after each pour, and before you reattach the lid.

Precipitation happens when the NaOH "un-dissolves" from the water and falls to the bottom of the container, usually due to a temperature drop to 65F or below. The undissolved or precipitated NaOH often solidifies into ice-like chunks or crystals at the bottom. That IS a problem and DOES affect the concentration of the remaining liquid.
Everything @AliOop said.
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I don't make huge amounts of MB, maybe about 2kgs at a time, but I thought that maybe over time I was losing enough lye to make a difference. Thanks for the tip about wiping the pouring edge dry, hopefully that's it!
It does make a negligible difference to the amount of solution left, but not the strength of that solution.

For me, wiping after (not before) each pour is the key to minimizing the crusties around the lid. Due to the configuration of the pouring spout on my repurposed laundry detergent jug, I can't seem to completely eliminate it, but at least the crusties that remain are around the inside pouring spout only, and don't make a mess when I twist off the outside cap. Hopefully that makes sense? ;)
@Vicki C, I am starting to see lye chrystallize around the top of my MB jar, it kind of flakes off when I open it. Why is that the crystallization would not be a problem if you MB at your "regular" concentration, is it just that it is less concentrated and as a result you have less flaking? It a little worrisome, and I'm having some differences with trace, so I was actually thinking of either lowering my superfat percentages or just going back to mixing lye water for each batch instead of MB'ing.
It's just dried Lye Solution...the water has evaporated leaving dried Sodium Hydroxide residue. If your container contained salt water or sugar water, you would have dried salt or sugar residue. All you need to do is just wipe the spout before putting the lid back on.