pH Deviations and Overheating When Preparing Dehydrated Culture Media

Preparation instructions belong to the exact product

One g/L recipe or sterilisation time cannot be applied to all dehydrated media. Agar, broth, selective formulations and product variants may require different instructions. Begin by confirming that the current technical document matches the product code in hand.

Names such as Microinstant or Non Animal may distinguish a formulation or variant. Copying instructions from a similarly named medium can prevent the expected pH or performance from being achieved.

Do not blame only the meter for a pH deviation

Unexpected pH may involve water quality, incorrect quantity, incomplete dissolution or mixing, container effects, heating or measurement conditions. Read the product documentation to establish the preparation stage and temperature at which pH should be checked.

Correcting a deviation by adding acid or base without a defined instruction may create an unauthorised formulation change. Such an adjustment should only be considered within the applicable instructions and laboratory procedure.

Overheating and repeated melting

Excessive or repeated heating can change the properties of some media. More heat does not necessarily mean better preparation or an appropriate sterilisation process. Follow manufacturer limits for selective supplements and any remelting steps.

• Do not apply one autoclave or microwave recipe to all products.
• Record preparation quantity, water source and heating conditions.
• Assess appearance, pH and required performance checks under the applicable procedure.

Which records help with a recurring problem?

Record product code and lot, TDS version, mass and volume, water source, equipment, preparation steps, measurement temperature and observed deviation together. Do not use a nonconforming batch before assessment; request product- and lot-specific technical clarification from the manufacturer where necessary.