As a cosmetic formulator one of the most common decisions you’ll have to make is to decide how large a batch you need to make. To best determine this you need to first answer the question of why you are making the formula.
Why are you making it?
There are a number of reasons you might make a cosmetic batch but the primary ones include prototype development, prototype testing, consumer testing, scale-up and production. Generally, each of these will require a different size batch.
When making a new prototype you may be tempted to make very small batches. This is particularly true when you don’t have access to a large quantity of your test raw materials. I’ve seen people create batches as small as 100g. Don’t do this. The smallest batch size you should make is 400g. It fits nicely into a 500g beaker and the quantities of the component raw materials are still large enough that you can accurately measure them. Making smaller batches increases weighing errors. Your first batch of any new formula should always be about this size. More than this is a waste of chemicals and less leads to too many weighing errors. Of course, if you are making a very simple solution formula, you can go as low as 100g as long as the ingredients are not less than 0.1%.
To test a formula, you are going to need larger sized batches. The exact size will depend on the type of testing that you are doing. If it is a simple 10 person panel test, a batch size of 800 – 1000g should be fine enough. But if you are doing a full stability test, you may need to make a few kilograms of your batch. Calculate out exactly how much you need and add 10% more. When you start to make mid sized batches it’s always good to have extra in case you need more product than you thought.
Consumer tests typically require full sized bottles for a number of consumers. The smallest consumer test is approximately 30 people but it’s not uncommon for some home use tests to have 100 people or more. This means a batch size of 5 gallons to 50 gallons. For these types of batches you do not need to add the 10% overage factor, 3 – 5% extra is usually enough. Often you can make extra samples and run a concurrent stability test with these types of batches. In fact, you can also use this batch to do your scale-up testing.
For some small manufacturers you won’t make batches just to test the scale-up of a formulation. Your scale-up batch size is your production batch size. (50 – 300 gallons). But if you work for a big company you will often have to create a scale-up test to see how the formulation will behave when it gets moved to the production sized batches (2000 – 5000 gallons). For these types of batches you do not really have to make much extra (say 1-2%) because even a small % over will be a substantial amount of product.
Final thoughts: Before you make any batch you need to think about how much you need and calculate out exactly the amount you want to make. For smaller batches make more than you need. Also, measure as precisely as possible. For larger batches don’t worry as much about exact measurements. A larger batch size means that small measuring errors will not have a significant impact.