Sorry, I didn't get any notices of posting until this morning and am not all that great at watching threads.
As I mentioned these probiotics have wild claims about how many bacteria are present which are so far off it should be illegal to sell them as false advertising. However, they appear to have what they say they do and I had used a source that has validated these suppliers for accuracy of contents. Storage is a big problem for living cultures and they don't like the lyophilization process and generally lose 99% unless a lot of care is used in drying them down in a vacuum freezer. Since those machines are now considered to be tools for manufacturing weapons of mass destruction I suppose the methods used today have to accommodate the realities of the world today.
What you are seeing is the effect of this. Yes, I continue until they curdle the first go-around and it can take overnight. I didn't mention it explicitly and I apologize for that. These were quick and dirty instructions and I often forget that people really don't understand the techniques well. Having worked in micro labs since 1971 I take it for granted.
They key to doing this successfully is to not use too much milk. Roughly 50ml to get started is sufficient. Sometimes it doesn't curdle but you get small lumps instead. This is okay and you can expand from there. The other thing to take care of is using as close to sterile technique as you can. You don't have to go insane about it but whatever is on your hands can end up in the culture and these often overwhelm the yogurt strains so some amount of care is necessary. I would wear your COVID masks and fresh gloves. wash my hands while wearing the gloves if I get them contaminated. Normal cleaning of the jars is sufficient as long as you rinse them with very hot water. That is sufficient to sanitize them but not sterilize. If you want to sterilize stuff I recommend using 10% fresh bleach solution and immerse for 10 minutes then rinse well with hot water. I usually don't bother as my techniques are good. But, it might be necessary. The first set of cultures is important. I also use food grade 5 ml sample tubes with attached snap caps. Something like these:
https://www.amazon.com/GBSTORE-Cont...=food+grade+5+ml+tubes&qid=1616308741&sr=8-44
I freeze down each Probiotic separately in small ziplock bags and make-up 10 or so as Master Cultures. When I want to start a fresh batch for consumption, I thaw one each of the master cultures with probiotics into 50ml of milk and grow them up then combine them together and expand from that. Generally, in a -20 freezer you can keep them 2 years or so but you will lose some viability over time which will be seen in longer incubation times. When it gets over 8 hours start fresh again. From the combined batch I make up 10 or so tubes and freeze these down in a separate bag. These become the Secondary Culture. These I use to start each batch for consumption. I don't bother labeling each tube but each ziplock bag is important to write the contents and date you made it.
I don't judge by smell at all only the consistency of the milk after culturing. After a while, you get a feel for it and it becomes second nature. Really it doesn't take up a lot of time.
You can also use an Instant Pot on the Yogurt setting for very large batches if you have more people eating yogurt. As I am the only one in our house eating these a batch lasts me a week eating one per day.
I need to add that any off-color is a sign of something gone wrong. I have had problems with pink growth on the surface in the refrigerator. Usually, this is from either a fungus (that continues to grow at refrigerator temperatures) or bacterial contamination. If you see that then you are harboring a contaminant and it must be tossed and start fresh.
A quick explanation is that microbes we are interested in grow at body temperature. Soil bacteria such as pseudomonas etc. grow at room temperature. Every organism has an environmental niche of temperature, pH, etc. and will grow well in these conditions but not in others (thankfully). So, our organisms of interest will not grow well (they grow at very slow rates at 4 degrees C) but others like that temperature so a contaminant can easily overwhelm our cultures. Also, every probiotic I know of is contaminated with "normal" yogurt cultures in addition to the ones we are interested in. These appear to be adapted to grow better so eventually also wipe out our minor strains in the culture. The normal Acidophilus strains are fine and healthy so it isn't a bad thing but after time you lose the additional strains. This is why I don't passage from current cultures (use one container to make a new batch without thawing any frozen secondaries) very long. I have squeezed out 3 passages but don't recommend doing that. I get lazy too. If I had a working lab I would actually work the details out and know for certain what is happening but in lieu of that, I am using my guestimate of what I think is happening.
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Amazon answers can be hit and miss. At least, you didn't get one of those "I don't know" answers. 
