Quinoa batter can typically be refrigerated for up to 2-3 days before it starts to sour due to fermentation.
Quinoa batter, like other grain-based batters, contains natural sugars and starches. When refrigerated, wild yeasts and bacteria present in the batter begin to ferment these components. This fermentation process produces lactic acid and other byproducts, which cause the batter to develop a sour taste and potentially an unpleasant odor. The rate of fermentation depends on several factors, including the ambient temperature of your refrigerator, the initial cleanliness of your equipment, and the specific composition of the quinoa and any other ingredients used in the batter. Generally, you'll notice a change in smell and taste after about 2 days. After 3 days, the sourness will likely be too pronounced to produce palatable results. It's always best to use your senses – smell and taste – to determine if the batter is still good. If it smells strongly sour or has an off-putting odor, it's best to discard it.
To extend the shelf life of your quinoa batter, store it in an airtight container in the coldest part of your refrigerator. Adding a tablespoon of lemon juice or vinegar can also help inhibit bacterial growth and slow down the souring process, potentially extending its usable life by a day.