It's not just a you issue as I've had it happen, too! And thanks for the great question! In theory, we should just be able to take our favourite recipe and multiply it by 20 to get a large batch of 2000 g or 2 kg of lotion, conditioner, and so on. But I have found things are different when we get into higher amounts.
I'm not sure exactly why, but here's my theory. The short answer is that we aren't measuring as accurately as we think we are measuring. The long answer is this...
Let's say we make a 100 gram batch of shampoo bars that contain 3 grams stearic acid to harden them. We measure 3 grams stearic acid into the batch and it makes a nice hard bar. When we get to the 2000 gram batch, we add 60 grams of stearic acid to the product and it's a bit soft. What gives?
If you have a scale that goes to 1 gram, you won't see if you had 3.2 or 3.4 or even 3.6. (It might flip back and forth from 3 to 4, but you don't know exactly how much we have!) So we might be using 3.5 grams of stearic acid to make the product feel harder. When we make the 20 x or 2000 gram batch, we really should be using 70 grams (3.5 x 20) instead of 60 grams (3 x 20), and that accounts for the softness!
If we do this with an emulsifier, it can lead to a ruined batch of lotion. At 100 grams, we add 5% emulsifier to a pretend recipe. Take it to 1000 grams and we add 50 grams. But we might be adding anywhere from 5.1% to 5.9%, which means we might need 51 grams to 59 grams are actually required to make the product work! What a difference!
You can see how it might mess with your pH. If you add more of an acidic or basic thing, you've altered the concentration, which changes the pH. (Click here for more about pH and concentration!)
What can we do? I suggest getting a small scale for measuring essential ingredients before you scale up. For instance, measure things like your emulsifiers when you're making a lotion that you might want to scale up. You'll also find a lot of use for it if you like extracts or cosmeceuticals.
I bought this one from Mountain Gems, a jewellery store, in Burnaby, B.C. I think I paid $13 for it, so you know you don't have to spend a lot. You could also use an epoxy scale, but they tend to be more expensive. And someone on the Dish forum suggested this scale (Canada). Apparently, Lotioncrafter carries it, too.
This is one of the reasons that some people say not to make really small batches like 100 to 200 grams. It does make sense, but do you want to make 500 grams (something like 4 - 120 ml or 4 ounce bottles) of something you've never tried before? And I hope you wouldn't make a 100 gram batch of something and dash towards making a 2000 gram batch the next time. I think it's okay to make 100 gram to 200 gram batches, just think about measuring those essential things before scaling it up.
MIXING LARGE BATCHES OF PRODUCT
A question about large batches was posed to me in an e-mail, but I can't find the original, so I'll have to paraphrase...Can we use those giant paint mixers for larger batches?
Yes. I have one that I attach to my drill. It is awesome! Mine looks like a giant cake mixer thingie - the second from the left side going clockwise - and it works really well!
You also asked about shear...which I'll address in an upcoming post!
HOW LONG CAN WE KEEP DISTILLED WATER?
In this post, Krogers asks: What I was wondering is how long does distilled water last? How long can you safely keep a bottle around? I refrigerate it. Does it need to be refrigerated?
Good question. I'm not really sure. Time for some research! (And I have to point out that I ended up at quite a number of cigar enthusiasts', doomsday preppers', and beer brewers' forums. The internet is full of such weird and wonderful things!)
In my reading, I've seen some people argue that it should be disposed of once opened, while others argue for three to six months. This educational site recommends treating your water and replacing it every six months (and this isn't distilled water). I've seen some say it's good for as long as the bottle holds up.
I keep my opened plastic bottle of distilled water for a month or so in my unheated workshop in a dark, cool place and I feel comfortable doing that. When the weather gets warmer, I put it in the fridge as I really don't want condensation in the bottle. In an ideal world, I think we would buy a new bottle every time we go into the workshop, but this isn't feasible for most of us due to availability of distilled water and time constraints. Once the bottle is opened, I wouldn't consider it sterile any more, but I don't think it's going to start growing huge amounts of mould or algae.
Remember, this is only my opinion based upon what I've read. Do you have another opinion or some things from reputable sources I could read?
Have a wondering? Visit this post to ask your question or pose your problem! You can comment on other posts or write to me, but I do check that post first!