When fermenting any kind of sugar water solution then there are small quantities of by-products such as methanol produced.
For the most part, this is no issue, however when you distill and concentrate the alcohols in the wash (including methanol) then it can become an issue. This will be removed in the first portion of distillate.
Distilling with fruit
When using fruits as a fermentation base, we can't guarantee the amount of methanol in the finished distillate, however discarding the first 50ml is good practice and will get rid of most of the methanol that may have been produced.
Methanol is produced during fermentation from fruit pectin, which is contained in fruit skins mainly. By taking care to not introduce too much fruit skins in the fermentation substrate, there won't be any issues at all.
If making gin (by soaking/steaming berries) or adding any other types of fruit in the boiler, there's absolutely no risk of adding methanol since the berries don't undergo the fermentation process. You shouldn't expect frothing issues either, unless the fruits are full of sugar.
Note: When doing multiple runs, for the second and third run it typically does not produce methanol depending on the unit you're using.