At one time I used mineral oil in Small Hive Beetle traps. The directions warned not to spill the oil in the hive as the bees suffocate if it gets all over their bodies. Unfortunately while placing the trap on a frame I spilled a bit on a bee. It struggled and died 
It broke my heart.
That was years ago and I threw away those traps.
Maybe a small drop of mineral oil on top of a frame would soak into the wood and not get on the bees. If I were to try the mineral oil, I would put the drops on the frame outside the hive, let it soak in , then place the frame in the hive.
I know, it was just one bee but I felt so terrible.
Ok, So technique definitely matters! I would have felt bad too.
As, I think I said before, there is no garlic taste in the honey.
Thanks for the great link.
ok, great. I didn’t realise that’s what it was.
Hi all
I checked with the beekeeper who told me about the tonic. I got some details wrong. The 2 litres was the size of the batch he makes at any time. He feeds the bees only 750 mls each time.
As someone suggested, he also does it in Spring. So that’s 3 weeks before Winter, so in Autmun/Fall and again at the start of Spring.
Some may ask, why three weeks? He mentioned he did it that long, so a full generation of bees would get some, or something like that.
Best wishes