What should kept constant when making a yogurt?

When making yogurt, it's essential to keep the temperature constant during fermentation, ideally between 110°F to 115°F (43°C to 46°C), to ensure optimal bacterial activity. Additionally, the ratio of milk to starter culture should remain consistent to achieve the desired thickness and flavor. Lastly, use the same type of milk (whole, low-fat, or non-fat) to maintain uniformity in texture and taste.