I imagine you can not mix flavors and steep for a few weeks and then add PG/VG mix but what about nicotine?
MadVapes does this on a large scale. Their house juice line (top vapor) comes to the retail locations in big 480mL bottles, pre-steeped, and 0mg nic strength. When a customer wants a bottle of juice, they have a piece of software that calculates what setting the nicotine dispensing unit (in the retail store) needs to dispense for that size bottle and nic strength, and prints a label for the bottle.
FWIW, MadVapes stores use 300mg/ml PG-based nic. (and yet some don't even use gloves, I used to hark on my coworkers about it when I worked there)
I do this and am able to reach a higher temperatures in fast-steeping methods.
When making travel drippers I'll usually prepare my wanted nicotine amount in a syringe and slowly add nicotine to a bit of juice with vigirous shaking in between each addition. I do this at 2ml a time until my 10ml dripper is full.
You should absolutely add nicotine later. Steep first, then add nicotine. This is especially necessary if you are using the heat steeping method. First rule about nicotine is that it should be kept sealed away from oxygen. Next is that it should be kept out of the heat. Heat and oxygen breaks it down and will degrade the nicotine as u/Robwier stated earlier. If you want to speed steep, I would suggest using a thermos. Make sure you use a glass bottle as well. Pre-heat the thermos with hot water, fill it back up, add the glass bottle, seal the thermos up. Try to put it in a warm place like in your basement where the boiler is. If you have a nice hot copper pipe exposed, place the bottle/thermos next to it overnight. Heat steeping at around 85-90 degrees for 8 hours yields the same results and letting it sit for 2 weeks. This was a study done by an ejuice redditor a while back. He worked in a lab and had access to some serious equipment to do the study. Those were the results he came back with. With I saved the study for reference but didn't. I've found that this works very well. (Experience: Mixing juice for the past 2 1/2 years professionally) Let me now if you have any questions. Happy mixing! This gives a good explanation about storing your nic as well: http://www.nudenicotine.com/category/e-liquid-chemistry-education/
That's the kind of super important info you randomly run into from reading every thread in this subreddit. Quick question - How do you do this on a bigger scale? Also, what is your opinion on steeping with an ultrasonic?
If you want to do this on a bigger scale, I would suggest getting some measuring equipment. I have a different sizes of graduated cylinders that I use depending on the size of the batch that I make. I will typically calculate based on the normal 30ml bottle and multiply it by how many mls I'm making. If you measure by drops, use a grad cylinder to calculate the exact amount that you want to use for making around 10 bottles. Example: if it's 10 drops per 30ml, that would measure out to 100 drops. Put 100 drops in a grad cylinder to figure out the exact amount that's need. After you do this, you can now use a syringe or a just take the top off of the concentrate and dump that exact amount in the grad cylinder to make your big batch. This will safe you a great amount of time. When making big batches, I like to use mason jars. Make sure you clean them very well using boiling water after purchasing them from the store. Remember, your environment/lab must always be clean before mixing. Back to the mixing. You can start out with a smaller mason jar that you can make 300mls(10oz) in. After you mix all of your ingredients, seal the top and heat steep. This is when it's important to use glass. I like to start with water that is around 150-160degrees. This is around the max temp that my sink puts out. Put the sealed bottle in the hot water for a couple of minutes, take it out, shake it, and repeat. Store the bottle in a warm place for extended steeping. After you have heat steeped it, add your nicotine. Now you are ready to bottle.
Correct, you need to add PG and/or VG before beginning the "steeping" process...but holding off on the nicotine is not an issue. In fact, adding nicoting after steepig has many advantages.
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Steeping/breathing can reduce nicotine content. Different recipes require diferent amounts of steeping/breathing. Result? Inconsistent nic levels flavor to flavor...unless the nicotine is added after steeping.
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If your nicotine preference changes, or you make juice for someone else... no probalo.
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You'll be able to taste the juice better as you judge it through the steeping process without the nicotine present.
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If a new juice tastes bad, you'll know the nicotine wasn't the issue.
I like to steep my juices a bit further after adding nicotine.
After you add your nic into the presteeped solution what do you do next? Do you just give it a good mix with a frother and then vape, or do you just mix it up and let it sit another day?
My normal steeping process is 2-8 hours in a food dehydrator, shaken every half hour to hour, followed by 1-2 weeks in the closet, shaken every few days.
When I combine pre-steeped juice with nicotine, I usually just shake it a bunch and wait a day or two. If the juice is 70% VG or higher, I give it one hour in the food dehydrator to thin the VG and then shake it again.