Real preservatives need to be added to your formula by weight. So this means you need to buy yourself a scale to weigh out your ingredients. I prefer to work in grams instead of oz, smaller increments and easier math.
The amount of preservative needed for your formula will depend on the type of preservative you choose. My favorite is Liquid Germall Plus and I use the max allowed in my FSG, which is .5%.
You will also need to buy a good thermometer. Preservatives need to be added at certain temperatures, again this will depend on the one you choose. LGP likes to be added at around 45C or 113F.
Preservatives will only keep NEW nasties from forming in your creation, but they wonít kill any that are already there! That is why it is very important to make sure all of your equipment is clean and sanitized. I run everything through the dishwasher and spray them down with alcohol first. I only use glass or stainless steal because they are the easiest to sanitize. Use bottled distilled water to make any creation needing water in it, I buy mine at Target for $.89 a gallon. Always use NEW containers to store your FSG in. Re-using old conditioner bottles etc. is a no-no. New containers donít need to be washed out first, they are considered clean from the manufacturer. If youíre going to do, do it right. You deserve that, donít you?
While you seeds are boiling, take you clean bowl that you will be working with and set it on top of your scale. Now push the tare button so that the weight is Ď0í. This will give you the weight of just the ingredients, not the bowl + ingredients. When the gel is done, strain the seeds out, and weigh out the gel. Add any extra stuff, like agave, honey, aloe vera, oils, fragrance etc. Now that everything is in, you can figure out how much preservative to add.
For easy math, weíll say everything added weighs 400 grams (just over 14 oz).
.5% of 400g = 2g
So, for this batch you will need to add only 2 grams of LGP to your FSG when it has cooled down to at least 113F. Stir it in well, and pour into your container.
The link that Kathymack provided gives some good info as well. Although Iím one of those that donít believe that GSE is a proper preservative.
is a great place to buy preservatives and equipment, like scales.
has good prices on containers and lots of other goodies.