Why does chocolate bloom?
Bloom looks like one problem but it's actually two different ones, with opposite causes and opposite fixes.
The kitchen answer
A dull, streaky grey-white surface is fat bloom -- a crystal problem. A gritty white film is sugar bloom -- a moisture problem. Both are cosmetic, not spoilage, but they need different fixes.
What's actually happening
Fat bloom happens when cocoa butter -- still liquid-ish, or sitting in an unstable crystal form -- migrates to the chocolate's surface over time, especially with temperature fluctuation (the chocolate warming slightly, then re-cooling), and recrystallizes there into large, dull, whitish-grey crystals. See Chocolate & Cocoa for why cocoa butter's crystal structure is unstable to begin with if it wasn't properly tempered.
Sugar bloom is a completely different mechanism: surface moisture (condensation from temperature swings, humid storage, or chocolate moving from a cold fridge into warm, humid air) dissolves surface sugar. As that moisture evaporates, the sugar recrystallizes on the surface as a grainy, gritty white film -- visually distinct from fat bloom's smoother streakiness.
What does that mean for your recipe
Prevent fat bloom by keeping tempered chocolate at a stable temperature -- avoid repeated warm/cool cycles, and don't store it anywhere near a heat source. Prevent sugar bloom by avoiding condensation entirely: don't move chocolate straight from the fridge into warm, humid air unwrapped, and store it airtight.
What can go wrong
- Chocolate stored near a heat source or in direct sun: temperature fluctuation encourages fat bloom even in properly tempered chocolate.
- Chocolate moved from fridge to room temperature unwrapped: condensation forms on the cold surface as it warms, directly triggering sugar bloom.
- Chocolate re-melted and re-set without proper tempering: both forms of bloom become more likely once the crystal structure is already disrupted.
- Assuming bloom means spoiled: both forms are cosmetic and textural, not a safety or freshness issue by themselves.
Try it yourself
Same tempered chocolate, two different abuses:
- Temperature-cycle one piece deliberately (a warm spot, then the fridge, repeated a few times).
- Move a second piece straight from the fridge into humid air, unwrapped.
- Keep a third piece as a control at stable room temperature.
Watch for: the temperature-cycled piece developing smooth, greyish streaks; the condensation piece developing a grittier white film; and the control staying glossy -- visually distinguishing the two failure modes side by side.
Go deeper
Fat bloom and sugar bloom are both, at their core, a stable structure losing out to a less-ordered one under the wrong conditions -- the same category of problem as uncontrolled crystallization in fudge, just involving cocoa butter or sugar crystals on a chocolate surface instead of a whole batch of syrup.