Your sugar will turn brown as a result of a chemical process called caramelization.
Caramelization in sugar occurs when the sugar is heated to a high temperature which turns it brown.
Sugar can also turn brown when the sugar molecules break down and break apart into smaller molecules or combine with each other to make larger molecules.
Sugar also can react with oxygen, lose water or even cause new compounds to form which can lead to brown sugar.
The sugar molecules can react with each other and produce new compounds and the compounds are then what gives the sugar it's caramel color and it's characteristic flavor, aroma and it's golden brown color.
Sugar can also become hard as a brick as a result of moisture and exposure to air.
Granulated sugar will harden and become hard as a brick when exposed to moisture and brown sugar can dry out and harden when it's exposed to air for too long.
If the bag of sugar is not fully sealed it can cause the sugar to dry out and harden.
Sugar can also become hard over time as a result of aging although moisture is the most common reason for sugar becoming hard.
You can use a hammer to break the sugar up and still use it.
Another way to quickly soften the hard sugar is to remove it from the package and place it in an oven safe container and heat it at 250 F.
Watch the sugar closely and turn the oven off as soon as it's soft and use the amount of sugar you need right away as the sugar will harden again as it cools down.
Sugar does not get moldy because sugar is actually resistant to microbial growth.
Sugar is a stable substance which does not harbor any bacteria or mold like other foods can.
The lack of moisture in sugar also deters the microbial growth.
Sugar actually has an indefinite shelf life and can last for decades.
Although sugar can become hard but it remains safe to use for years and you can break the hard sugar up and it will also dissolve in liquids.
While the sugar itself does not grow mold the sugar bag when kept in damp locations can grow mold.
Granulated sugars can also become harden or lumpy and sugars in honey and syrup can also crystalize.
Even when the sugar has become lumpy or crystalized it still is safe to eat consume the sugar.
The best way to store sugar is to store the sugar in a cool, dry airtight container in an odor free location.
Store the sugar in a cool, dry place such as the pantry and away from any extreme temperatures and sources of chemicals and use a container with a tight fitting lid to prevent bugs from getting into the sugar and clumping.