This is the question above any other we are asked most frequently and is something that people get very confused about.
First and foremost, the term food safe cannot technically be applied to a glaze as supplied.
The final fired piece may be considered “food safe” however this is reliant on such a massive variety of factors outside of any suppliers control that there is no definitive answer. The clay body, form, surface texture, firing schedule, oxide addition and many other variables all need to be considered. Glazes with matt surfaces, crackle glazes or other non-glossy effect glazes should all be avoided for functional ware due to the possibility of the surface harbouring bacteria.
In general provided glazes are fired to maturity on a suitable clay body there should be no issue, however the only guaranteed way to have a piece deemed “food safe” is to have it tested by a certified ceramics testing laboratory. In the UK this is done by Lucideon and can be contacted by clicking this link.