Just realised I have been giving
Ds the comfort formula during the day but the ready made cartons we have been using at night is the basic stage 1 formula. The comfort doesn't come in ready made cartons ! Health visitor said no major issue but best to move him onto comfort all the time.
Came across this and found it a really good explanation. May be helpful to some of you.
"The reason for the 30 minute wait is that a litre of water takes 30mins to cool by 30C to the optimum temp for killing the bacteria (enterobacter sakazakii/salmonella) whilst still retaining as much of the nutrients in the formula as possible.
Adding formula powder to cold water is not considered a safe way to prepare formula as it does not kill off any bacteria that may be in the formula powder.
Once made up and cooled to drinking temperature the bottle has a life of two hours before it must be discarded and a fresh bottle prepared.
The absolute safest way to feed formula is using ready to feed cartons as they are sterile whereas powdered formula isn't (there is currently no known way to sterilise a powder without radiation).
The safest way to prepare a powdered formula feed is with 70C water then cooled and fed immediately to the baby. Bacteria (if present) should have been killed and not allowed chance to grow before baby drinks it.
The next safest is 70C water, cooled refrigerated for less than 24h then warmed and fed to baby. Bacteria (if present) should have been killed and cooled to a temperature that bacteria does not grow well at.
The next safest is powdered formula added to cool boiled water and fed immediately to baby. Whilst bacteria (if present) has not been killed, it is not given a chance to grow before being drunk by baby.
The next safest is powdered formula added to cool boiled water and stored in a fridge, warmed and fed immediately to baby. Bacteria (if present) has not been killed but stored at a temperature that bacteria does not grow well at has the possibility of growing whilst stored.
The next safest is powdered formula added to cool boiled water, warmed and then left out/placed in bottle bag before drinking some time later. Bacteria (if present) has not been killed, has been heated to a temperature that bacteria grows well at and then left - any bacteria that is present can multiply quickly.
Obviously, it's up to a parent to decide how to prepare formula, but it is worth baring in mind the age of the baby and health status before choosing which method to follow."
The below link has good info on the water temperature in a thermos.
Page 2 - http://www.firststepsnutrition.org/pdfs/StatementonnvacuumflaskssandtravellformulasystemssFeb2016.pdf
All the above has helped me to decide I'll either be making up in advance or using thermos for night time feeds / going out.