Potato density changes with age – by Karim Bahsoon

Potato density vs Age (expiration date of potatoes 1st March 2011)

As discussed we have been measuring the density change of the potato over a number of days. The potato was left out at room temperature and the density measurements were carried out using the same method as before (filling measuring jug with water to assess volume/mass change).

DATE MASS (g) VOLUME DISPLACED (ml) DAYS AFTER EXPIRY DENSITY (g/ml)
24/02/11 142 130 -5 1.092307692
25/02/11 142 130 -4 1.092307692
28/02/11 140 129 -1 1.085271318
01/03/11 140 129 0 1.085271318
03/03/11 139 129 2 1.07751938
07/03/11 138 128 6 1.078125

Potato Density vs Days After Expiry

The density change has been fairly minimal, and the precision of the scale (accurate to 1 gram) has perhaps hindered the experiment somewhat. Having said that there is clearly a negative correlation between density and age.

Drying out procedures (fridge/freezer/room temp.) vs. crunchiness/ crust thickness. (also noting mass change)

The drying procedures we looked into were; fridge drying (26hrs), freezer (68hrs), room temperature drying (1hr). We measured the mass change during the procedures and the crust thickness at the end. All the fries were blanched for 8 minutes.

Mass after blanching (g) Mass just before frying (g) Mass after frying (g) Mass ratio Average crust thickness (mm)
No Drying 13.978 (2) 13.978 9.186 0.66 0.407
Room Temp. 55.514 (8) 53.406 44.872 0.84 0.317
Fridge 28.968 (4) 23.3291 20.101 0.86 0.332
Freezer 22.34 (3)* 17.659 14.829 0.84 0.278

*number in brackets represent the number of fries in the batch.

Surprisingly, so far we have observed that the crunchiest fries have actually been produced from fries put straight into the fryer after blanching (dabbed with kitchen towel to remove excess moisture). This has been supported by the measurements for crust thickness with the thickest crusts being formed from the cooking process not involving any form of drying. The three drying procedures tested all produce similar crust thicknesses, approximately 0.1mm less than what was observed with no drying procedure carried out.

We also found, through tasting, that fries which weren’t dried were crunchier, more rigid. and browner.

Mechanical testing will hopefully provide better quantitative data to support the findings so far.

The mechanical testing will primarily focus on indentation testing of fries blanched for various times. We will perform the tests before and after frying and for fries which have been dried. The intention is to quantitatively assess how the mechanical properties are linked to the sensory properties which we have observed so far.

2 comments for “Potato density changes with age – by Karim Bahsoon

  1. Robert Souza says:

    Potatos of today seem to take longer to cook. Used to take 1 hr. @ 350 for a average potato. That same spud takes about 1-1/2 hour to cook. Any reason why?

  2. fototapety says:

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