No special instruments / meters available. Is there an approximate way to tell when the alcoholic fermentation has stopped ?
I am asking so I know when to add the MLF yeasts in.
Viniflora CH16 should be added to dry wine, immediately after the alcoholic fermentation. Viniflora CH16 should always be inoculated directly into the wine. No rehydration or reactivation is required.
Don't rule out the approach of tasting the wine, as a complementary test. It is not really a fermentation test but you can have an idea about how much sugar is left in the must (wine?). Of course, you can taste the wine easily if the fermentation tank/bucket has a spigot. I enjoy tasting the wine several times along the fermentation period and having a feeling of the fermentation evolution. I know that the wine is ready for the secondary fermentation when it feels dry.
If you don't have an hydrometer, just keep a close eye to the airlock and give it a few days (3-5) after the activity has stopped. Mind that this is not the correct way to do that and there's no guarantee that your fermentation has finished.
The only proper way to know that is to take periodic measurements of the density and determine when the gravity has stopped declining.
Hope that helps!
CO2 in suspension will cause bubbles to come out of the airlock long after the fermentation is done. It is an indicator, but not a precise one.
Experience will tell you that for a particular yeast/wine, fermentation takes, for instance, 5 days to complete if all parameters are identical. Again, it is not precise.
You should get an hydrometer and mesure gravity to be sure. Anything else is a guess.
If you have no other instrumentation, look at the airlock.
If the brew is fermenting, there is always going to be positive pressure against the liquid in the airlock, even when fermentation is relatively slow.
If the room temperature drops and the liquid seems to be creeping back towards the brew, this indicates negative pressure, and suggests that fermentation has either stopped, or that the temperature is too low for the yeasts to continue to work.
Seriously though, for a couple of bucks it's generally easier to get yourself a hydrometer, and take a measurement to see if you've reached your target gravity.
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