A food is bacteria-safe if it is:

The understanding of food safety in relation to bacteria involves the concepts of pH and moisture levels. Foods that are neutral and moist or acidic and moist typically provide an environment conducive to bacterial growth. However, foods that are dry and have an acidic pH are less likely to support the growth of bacteria.

Bacteria thrive in environments where there is sufficient moisture and in neutral pH conditions. High moisture levels combined with a neutral pH (around 6.0 - 7.0) offer ideal conditions for bacteria to proliferate. Conversely, an acidic environment, usually characterized by a pH below 4.6, can inhibit the growth of many bacteria.

When considering the dry aspect, a dry food product generally lacks the moisture necessary for bacteria to grow, making it more resistant to bacterial contamination, especially when combined with an acidic pH. Acidity, combined with low moisture (as seen in foods like dried fruit or certain cured meats), creates a hostile environment for bacteria, making it safer from a microbiological standpoint.

Thus, an acidic and dry environment significantly reduces the risk of bacterial growth, which is why this combination is recognized as bacteria-safe.