A syrup with potassium iodide and after baking soda colors brown.

I have to start by saying that I do not have a tailor-made osolution to avoid discoloration.  

The composition contains iodide, sugar and a small amount of alcohol derived from the   mint Spiritus.. Inevitably, oxidation iodine will be formed by the present atmospheric zuuurstof. It is known that the addition of sugar (see mint syrup) reduces the amount of dissolved atmospheric oxygen. But you dissolve bicarbonate in water and for this you would need about 105 ml of water according to Muijn calculation. Only 195 coin syrup remains.  

I have found the following text in the literature: When mixtures containing potassium iodide, sodium bicarbonate or other alkaline substances and alcohol were stored for some time Iodoform was produced from the free iodine released by Atmospeheric oxidation.  

From this we must conclude that we need to reduce the amount of dissolved oxygen.  

We could therefore try or dissolve the bicarbonate without   warming (may take a long time) in eg 275 ml of mint syrup   in a closed bottle.   This Is feasible then We add KI and see if it also solves it. The preparation can be terminated by putting on volume with mint syrup.  

One, another possibility exists in solving 10 g NaHCO3 in 105 ml of water, back at room temperature in a closed bottle under gentle stirring with the magnetic stirrer. Ideally the saturation would be with nitrogen. After dissolving we add 180g granulated sugar and 100 g of water and let the sugar dissolve in the bottle under gentle stirring with the magnetic stirrer. After dissolving the sugar we dissolve KI and add the mint Spiritus and bring it to volume.  

I can't assure that we avoid brown staining. The last question, which I still ask me is: Would the addition un help an antioxydance? ". Since we are dealing here with a light of solution we have to use after bisulphite conc = 0.1%   à 0.2%. It should in any case be added for the insertion of KI