As an expert sommelier and brewer, I can tell you that sour beers do have the potential to be lower in carbs compared to traditional beers. This is because the microbes used in the fermentation process of sour beers, such as lactobacillus and pediococcus, are capable of metabolizing a wider range of sugars and starches than the typical beer yeast used in regular beers.
The ability of these microbes to break down a wider variety of carbohydrates means that they can consume more of the available sugars during fermentation. This can result in a beer with a lower residual sugar content, which in turn means fewer carbohydrates in the final product. However, it's important to note that not all sour beers will necessarily be lower in carbs, as some brewers may choose to add additional sugars to balance out the sourness.
One thing to consider is that the sourness of these beers can sometimes be quite intense, and to counterbalance this, some brewers may add sugars or fruit to provide a contrasting sweetness. This addition of sugar may increase the carb content of the beer. It really depends on the specific recipe and brewing techniques used by each individual brewer.
In my personal experience, I've encountered a wide range of sour beers with varying carb levels. Some have been light and crisp with a lower carb count, while others have been richer and sweeter, indicating a higher carbohydrate content. It ultimately comes down to the brewer's intention and the specific ingredients used in the brewing process.
To summarize, sour beers have the potential to be lower in carbs due to the metabolic capabilities of the microbes used in fermentation. However, the addition of sugars to balance the sourness can increase the carb content. It's always best to check with the brewer or refer to the beer's nutritional information if you are specifically concerned about carb levels.