Addressing Water Evaporation in O/W Cream Formulations (Homebrew Scale)

It is understandable that you are experiencing significant water evaporation (around 20%) during the heating and mixing phases of your O/W cream formulation, especially with the prolonged heating required for dissolving ingredients like PVP and the subsequent emulsification process at 85°C.

Losing 20% of the water from your formula will indeed have a significant impact on the final product. Water is a critical component in O/W emulsions, affecting the stability, viscosity, texture, and the concentration of all other water-soluble ingredients. A 20% loss will likely result in a much thicker product than intended and can compromise the overall stability and performance of the cream. As the staff mentioned, adding water back later is generally not recommended as it can be difficult to re-incorporate properly and maintain homogeneity, potentially leading to an unstable emulsion.

For homebrew scale production (like your 4000 CC batch), while industrial vacuum mixers are ideal for preventing evaporation, there are practical steps you can take to minimize water loss with your existing equipment (Hot Plate and Dissolver):

• Cover Your Container: This is the most effective simple method. Use a lid or even aluminum foil to cover the beaker or container where you are heating and mixing the water phase. This traps the steam and significantly reduces evaporation. Ensure the cover allows just enough space for your Dissolver shaft.
• Optimize Heating Time: Heat the water phase ingredients to the required temperature (e.g., 70°C for PVP dissolution, then 85°C for emulsification) as efficiently as possible. Avoid prolonged heating at high temperatures before mixing the phases.
• Pre-heat Solid Ingredients: As suggested by the staff, if you are using a significant amount of solid ingredients in the water phase, such as Kaolin or even Glycerin if it's a large percentage, pre-heating them separately before adding them to the heated water phase can help maintain the temperature and reduce the need for the water phase to compensate for the temperature drop, thus shortening the overall high-temperature mixing time.
• Optimize Mixing Speed: While adequate mixing is necessary for dissolution and emulsification, excessively high mixing speeds can increase the surface area of the liquid exposed to air and generate heat, both contributing to evaporation. Use the lowest effective mixing speed required for each step.

Regarding suitable equipment for homebrew, beyond covering your container, look for mixers designed for laboratory or small-batch cosmetic production that might offer better temperature control and mixing efficiency compared to a standard hot plate and dissolver. However, these can be a significant investment. For minimizing evaporation specifically, a sealed or covered mixing vessel is key, regardless of the mixer type.

There is no universal "maximum time" for the process, as the rate of evaporation depends on many factors (temperature, surface area, airflow, humidity, specific ingredients). The goal is to complete the necessary steps (dissolving, emulsifying, cooling) as efficiently as possible. Focus on minimizing the time the water phase is exposed to high heat and air before and during emulsification. Your current process involves significant time at elevated temperatures (10 mins at 70°C + 20 mins at 85°C + cooling time), which explains the high evaporation. Implementing the suggestions above, especially covering the container, should help reduce this significantly.

By implementing these process adjustments, you should be able to reduce water evaporation and achieve a more consistent and stable final product without needing to compensate by adding extra water initially or adding it back later.