Cross contamination of flavours and more woringly bacteria, can occur if your pipettes or syringe is not thouroghly cleansed.
All bottles and beakers I use are storer aliased before use.
Flavour comes straight from the bottle.
My risk is minimal with regards to spreading any bacteria and I have no chance of cross contaminating my flavours.
I doubt people prefer your mixtures over your friends simply down to how you measure your recipe?
Whether by weight or volume, 10ml is 10ml, 10% is 10%, is it not?
You are no different than what I do. Just because I measure by volume doesn't mean I don't know how to properly sterilize my equipment. I think the risk is the same for you as it is for me.
You would think that the %s would equal each other in the end, and it should.
I think I may have figured it out though. I realize a lot of people assign a generic 1mg=1ml to all the flavor concentrates. Which is fine, if you make note of it on your recipe that you share. If I see that recipe and mix it up, it will be different because the flavors all have their own value and it isn't 1mg=1ml. Same thing will happen if someone tries to mix that same recipe using specific gravity for each flavor. It will be different from original but closer to mine.
Now, if you are like me and don't use recipes, it doesn't make and difference whatsoever. My friend on the other hand, follows recipes only. More often than not, his trial run recipes are trash. Now that I've sat and typed that all out, it still doesn't explain why people prefer mine over his, just why he has an ungodly amount of failed recipes.
I have no idea. I'm trying to figure it out. The obvious one to me would be if the flavors we use are different. However, not the case here. I thought it could be how he measures because he had much more success when he was measuring volume at first. One would only assume one would get better over time, not worse. He switched to a scale and has made almost no progress in 4 months. Obviously, there's an issue somewhere, I just need to find it. After ruling out flavors as the culprit I went to the next thing that I thought of which was how we measure. So, here I am.