Question. Yeast aerobic/anaerobic

[taatertony]

I have started a 5gal ferment with a lot of sugar and I am not sure if the yeast is up to it. The pack had been opened for about 6 months (youngs yeast compound). If I let some oxygen into the vessel am I right to believe that the yeast will multiply with the aerobic conditions? It's popping away nicely at the minute but I'm scared I'll get a 7% syrup with the yeast not interested anymore.

 

[YoungJames]

Is that the "Youngs Super Compound" from Wilkos?

 

[Insomniac]

Do you have an OG reading?

 

[taatertony]

The OG was around 1.11 maybe higher. It's the youngs super yeast compound. Its just that I've had a couple brews go wrong with ribena and vimto. Probably because of preservatives in the juice and me not boiling thoroughly.
For this brew I used post mix syrup from a new drink from coca cola called fruitizz, I boiled it for quite a long time.

 

[Insomniac]

I dont think boiling it will help with preservatives, it probably has sorbate in it, in which case no amount of air will make the yeast multiply and you will have to pitch enough yeast to ferment it from the start. You can do this by either putting in lots of yeast packets or by making a starter.

 

[taatertony]

Ahh I see how stupid of me. It actually does contain potassium sorbate. I'm pretty sure this brew is going to be alright as it's popping away at about 90 per minute. I had used a starter on it although could have give the yeast a bit more time.
So if any brew doesn't contain sorbate aerobic fermentation will multiply yeast cells?

 

[Insomniac]

Yup