I have been making pour over coffee now for about 1 year. I enjoy it. I hand grind the beans with a burr grinder and select a medium-fine grind. What I find though is that during the bloom time (about 45 seconds), about 1 ounce of coffee filters through. Is that normal and expected, or is that too much coffee to be filtering through during the bloom time? Any suggestions?
The drip-through of water during the bloom process isn't itself a cause for worry of a 'bad' brew as this process is meant to aid degassing of the beans prior to the main brew pour. The amount of drip-through you're experiencing is completely fine as long as the entire bed of coffee has been wet by the bloom pour.
However, if you reckon there is too much coming through, make sure you're not using too much water relative to your total brew weight in the bloom. If a significant fraction of your water is used during the bloom, and therefore less being used during actual extraction, it will affect the resulting flavour.
I'd argue that as long as the amount of water used for the bloom is less than 1/4 of the total brew water weight and the entire bed is being wet by it, no matter how much filters through, it should not affect the brew significantly.
I usually pour water just enough to wet the grinds completely. A few drops of coffee do pass through the filter, and that is fine. And of course wet the filter with hot water before you start your brewing.
As mentioned earlier blooming is to help aid in further extraction by helping expell CO2.As long as you think the coffee tastes good then it's fine. If you think your cup is lacking in something try changing it up. Maybe a finer grind or more/less water. Play around, that's the great part about coffee. It's subjective.
I usually have a little bit of water flow through as well when I bloom my coffee. My general rule of thumb when blooming is to add double the weight of coffee grounds in water. For example: if brewing with 20 grams of coffee I will bloom with 40 grams of water.