Dear
We have a sponge cake production line with an oven which has 3 burners on 3 zones
But we have a problem with water activity it's higher than limit
And if I looked at any window of the oven there was big bubbles inside the batter before now it doesn't show
In the US, water activity has a very specific meaning in food production. It’s not something that has anything to do with the actual baking. Rather, water activity is a measure of free water to determine potential bacteria growth.
From your description of visible bubbles during baking I take it to me the cake batter produces a lot of carbon dioxide gas during baking, creating a finished cake with a coarse open crumb. There’s a lot of factors that will cause this.
Chemical Leavening: if chemical leaveners are not thoroughly sifted into the flour it will produce a mix of large uneven gas bubbles throughout the batter. Sift chemical leavener in thoroughly.
Machincal leavening: whipped egg whites is mechanical leavening. Over whipped egg whites will produce too many air bubbles. If you are beating to stiff peak stage, reduce to firm or soft peak egg whites.
Too much leavening: Whether you use chemical leavening or mechanical leavening or a combination of both, make sure you are using the appropriate leaveners at the appropriate amounts.
Mixing method: the mixing method and amount of mixing is the number one cause of too much gluten development. Too much gluten traps too many gas into bubbles as soon as they form. It’s better to have a week gluten structure for cake batter so it does not trap as many bubbles. The high ratio mixing method works best to minimize gluten development.
Flour protein: strong flour will create too strong a gluten network. Make sure your flour is a low protein flour suitable for cake.
Ingredients temperature: if the liquid and fats are too cold they will not emulsify properly and the emulsion will break. Improper emulsification will create a coarse uneven crumb. Check the temperature of all your ingredients before mixing.
Finished Batter Temperature: after the mixing the temperature should be 68°F – 72°F (20°C – 22°C).