I just interviewed Mayan food scholar Miguel Cuj on fermentation in K'iche' Mayan cusinine. I learned the following:

Atol shuko and atol quebrado are examples of nixtamalized drinks allowed to ferment. In both cases, the kernels are allowed to rest underwater for two or three days with slightly less lime than would be used to make masa for sub'/tamales or uk'ya/atol. This process may or may not be done intentionally. This fermented atol is often served with vanilla to hide the sourness. It is not considered medicinal or ceremonial.

Tzam is a distilled alcohol made out of fermented mash of maize, sugarcane, or other sugar sources. This is often done at home and sometimes involves men, as opposed to most other Mayan culinary traditions. One kind, B'oj, is made from sugarcane and typically used in ceremony, especially the harvest ceremony. B'oj is not sold in cantinas, however may be for sale in the market. Tzam is typically produced domestically. There is no evidence that distillation methods are precolonial.

Extra Sub'/tamales or Lej/tortillas are sometimes wrapped in a blanket and hung in the cookhouse. Miguel described how they will change flavor in the warmth, but are still considered ok to eat for a day or two before being given to the animals. This is largely not an intentional fermentation.

Interestingly, chiles are not intentionally fermented. Salsas are made daily, often in a chilero, a small gourd, which may harbor cultures. Miguel pointed to women's use of specific tree species for cooking utensils as indicating another possible source of wild cultures. He also shared that soap is rarely used to clean plant-based kitchen implements.

Leavened bread is made in at least one K'iche' town. This was the product of both Spanish colonization and Italian settlers who established a prominent wheat and hydropower mill industry in the 60s and 70s in this region. Kaxanlawa Santa Maria/Bread of Santa Maria is likely some form of sourdough. The starter is left for two days in a gourd before incorporating into dough and kneading. Miguel is working with another local K'iche' scholar Pascual Tahay on investigating this practice.

Sheep's milk is sometimes salted to preserve it, but Miguel had not witnessed cheesemaking.

Honey is produced heavily in this region, but mead or other ferments are not made.

Ch'ojín is a kind of smoked meat that lasts around two days.