I am attempting to make a semi-sweet pure California Orange Blossom mead. I used 12.5 lbs of honey in a 5 gallon batch, but pitched a batch of yeast intended for a dry mead. My yeast - Premier Cuvee. I'd really rather experience a semi-sweet mead with this particular batch of honey, and I'd prefer (but am now open to, if necessary) to avoid any additions of acid or potassium sorbate. Given that this yeast can tolerate alcohol levels of up to 18%, I'm assuming that I need to/could add significant amounts of additional honey? But how much? 2.5 lbs? 7.5? Any advice is appreciated! I am 5 days into primary fermentation.
A few points and cautions:
1) if you do decide to stabilize and backsweeten, you will need to add potassium sorbate *and* potassium metabisulfite to effectively halt the yeast. Acid blend can be added to mead to taste (I do it at bottling, but I generally only use it for melomels) but has nothing really to do with stabilizing to backsweeten. I'm not sure what your reasons for not wanting to make these additions are, but unless you are producing for someone who has a sulfite allergy or something, there really aren't any technical downsides to the stabilizing additions.
2) A lot depends on the actual honey you used, but for 12.5 lbs in 5 gal volume, I'd estimate that your OG was ~ 1.090 (assumes 1.036 pppg) If you added 7.5 lbs for a total of 20 lbs, you'd effectively push your OG to 1.144...this should theoretically max out your yeast's "rated" tolerance. What I will tell you is that your yeast has no idea it has a rated tolerance...it will ferment until it is biochemically unable to continue, and that depends on multiple factors: nutrients, temperature, osmotic stress, pH, etc., etc. What this all means is that it's pretty difficult to predict how much honey to use such that your yeast will poop out and leave you with exactly the amount of residual sweetness you want. This kind of knowledge and confidence can really only come from reproducing the same batch over and over again under the same conditions until you fully understand how your conditions and yeast will behave in real life, in your brewery. Overall, it's much more precise to determine what ABV you want, ferment to dryness, stabilize, and backsweeten to your desired level of sweetness.
3) also bear in mind that sequential additions of fermentables can sometimes assist in pushing a yeast past its rated tolerance.
4) As others mentioned, decide if you really want a semi sweet, potentially 18+% ABV mead
Be sure to post back and let us know how you handle this, and eventually how things turn out!