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Asked on 15.04.2021.

Little bumps and air bubbles on a soft biscuit issue

Dear all, 

we baked biscuits for the first time. We start with a soft biscuit (two types with/without cocoa powder). We have a direct-fired oven, 40m long, with four-zone.

We faced with two problems:

-the line of unbaked dough in the middle of the biscuit

the line of unbaked dough

-The bigger challenge for us is little bumps and air bubbles on a soft biscuit. (We have docker holes on each biscuit.)

little bumps and air bubbles

To bring you closer to our problems, I sent our recept and description of the baking process below:

sugar 20kg, flour (T710) 125kg, palm oil 22kg, invert syrup 20kg, water 10kg, powder milk 2kg, cocoa powder 3kg, ammonium bicarbonate 1,4kg, table salt 0,7kg, sodium pyrophosphate 0,2kg, sodium metabisulfite 0,03kg, chocolate aroma 0,1kg, soy lecithin 0,5kg, soda 0,8 kg , corn starch 2kg, scrap (biscuit remnants) 15kg

Mix all ingredients in a mixer, except flour and pyrophosphate for 4-6 minutes. Then add flour and sodium pyrophosphate and mix for another 4 minutes.

The maximum quantity of mixer is around 450kg. The bigger quantity of 403kg we mix first 10 minutes, and add flour and pyrophosphate and mix for another 5 minutes.

We use this type of flour:

The moisture is 14,1%, Protein 12,3%, Gluten 28,4%, ash in flour 0,67%

For soft biscuits, we don't use pre-heating.

I fire zone Top 170C Bottom 135C

II Fire zone Top 200C Bottom 165C

III Fire zone Top 190C Bottom 130C

Time of baking is between 5min 48sec to 6min to 7sec


Thank you in advance, I hope you can help me!

Really appreciate!


Answered on 20.04.2021.

Hello Alma,

I want you to try the recipe suggested below.

If you try, please let me know if it solved your problems.

Your recipe basic rotary moulding recipe
flour 125 125
palm oil 22 22 17.60%
sugar 20 32 25.60%
invert syrup 20 4 3.20%
scrap (biscuit remnants) 15 10 8.00%
water 10 13 10.40%
powder milk 2 2 1.60%
cocoa powder 2 2 1.60%
corn starch 2 0 0.00%
ammonium bicarbonate dissolved in 2 kg water 1.4 1 0.80%
soda 0.8 0.6 0.48%
table salt 0.7 0.7 0.56%
soy lecithin 0.5 1.5 1.20%
sodium pyrophosphate 0.2 0 0.00%
chocolate aroma 0.1 0.1 0.08%
sodium metabisulfit 0.03 0 0.00%
221.73 213.9
Answered on 19.04.2021.

Hi Alma

About the blisters and recipe:

  • There is no need for Sodium metabisulphite for this type of dough. Why are you using it?
  • The inverted sugar amount is too high. I would put half of it. This high amount might lead to a false baked appearance due to the browning, besides the water binding caused by it.
  • Your water content is too low, even when considering water from inverted sugar. Should be minimum 6,5%. If you reduce inverted sugar, you should adjust water content accordingly.
  • Mixing time should be adjusted based on your dough temperarture, so it is mandatory that you measure it. It should not exceed 27º, I would reccomend 23º to 25ºC. If you are having difficulties to achieve this, you can try using ice scraps in cream stage (discounting from water content), and/or using cold water. If the mixer has jacket with hot water, don't use it.  Ice scraps must be analysed regularly for microbiological growing.

About the unbaked line:

  • Your oven temperature profile seems too low to me, considering the relatively short baked time for this number of zones (you mention that is 4-zone, but describe only 3 temperatures). I would try raising first zone by 10ºC, second by 20º (at least), last by 10ºC.  It is mandatory that you measure the moisture of the biscuit to do so (Usually, 1,8 - 2,0%). Try measuring moisture at the center and borders of the biscuit too, difference between border and center should not be higher than 0,8%.
  • Important: try to approximate the dough pieces on the baking band the more you can. This will help avoiding crust formation, that could lead to unbaked center of biscuit. 



Answered on 19.04.2021.

Hello Alma

I have read the problems you have and I am sure I can help you.

First I would change the recipe for you a bit.

Second, your baking profile should be hotter at the entrance than at the exit.

I would love to send you an email with a recipe that will direct you a little more.

Answered on 18.04.2021.

Hello Alma,

I have been reviewing the formulation and I would recommend to remove Sodium Metabisulfite as per the recommendation of Mr Hughes adjusting SAPP from 0,16 % Flour Basis to 0,9 % Flour Basis in order to neutrilize the excess of Sodium Bicarbonate.

The next steps would be to increase sugar from 16 % Flour Basis to 30 % Flour basis, reduce Invert Sugar from 16 % Flour Basis down to 6 % Flour Basis (decrease of the humectant used in order to allow less water binding).

Moreover decrease Palm Oil from 17,6 % Flour basis down to 16 % Flour Basis and increase Water from 8 % to 15 % Flour Basis (if allowed by the Dough rheology and the Flour absorption).

Moreover there is a non balance between top and bottom temperature which should be corrected by bringing the temperatures of top and bottom closer to each other achieving a highest bottom temperature in the 1st Zone and possibly in the 2nd Zone. The high top temperature in the 1st and 2nd zone is causing the skinning of the surface based on which no water vapor diffussion from inner out is occurring.

Finally ash content of 0,67 % is high hence the latter should be corrected below 0,55 %.

I wish you good results.

Answered on 16.04.2021.

Hi Alma,

The dough should be mixed until it forms a mass that can be compressed into a ball Excessive mixing once the flour has been added can result in gluten development which can cause shrinkage and distortion of the dough pieces The quantity of invert in your recipe seems excessive and would cause browning potentially making the biscuits look baked whilst the centre is unbaked

Answered on 16.04.2021.

Hi Mr. Andrew Hughes, 

Thank you for your answer and support.

It is a rotary molded type of biscuit. Tomorrow, in one mixture, we will try to dissolve the Ammonium Bicarbonate in water separately, before adding it to the mixer. (I will send feedback)

We have a dough mixer, the specification is below. Do you have some recommended time for the final mixing stage with the flour?

Also, I send again photo where you can see a line of the unbaked part.

the line of unbaked dough

Best regards, Alma

Answered on 16.04.2021.


You mention a soft biscuit do you mean a rotary moulded type or a dough made on a cutting machine as I see you are using Sodium Metabisulphite

I couldnt see the line of unbaked biscuit dough you spoke about but for the other problem I would suggest the following

Dissolve the Ammoniium Bicabonate in water seperately before adding it to the mixer  as if its undisolved you will get blisters on the surface after baking.

The final mixing stage with the flour seems quite long are you mixing the dough on a spindle mixer ?

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