Dear MTB,
I dont know ler, I bought 老行家 lao hang jia. The birdnest can last for 2-3 months and must finish within 21 days after open. They claimed that no perservative, not using vacuum packing.
Eventhough I bought those with rock sugar, it is not sweet at all. And it is abit crunchy, dry & fishy. So, I will reboil it with rock sugar and red dates to taste better.