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When cooking sous vide, will shredding the potatoes, instead of cubing them, work just as well or could it have unintentional consequences?

Context:

I am trying to improve my mashed potato recipe to get more consistent results. Unfortunately, I don't have a ricer, so I have to mash them by hand. I have previously tried mashing them in the bag, but I ended up missing several cubes of potatoes. By simply starting out with them shredded, would it make it easier in the end? But I'm also concerned it might change the texture negatively. I figure it would also allow them to cook more evenly.

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    What kitchen equipment or tools other than a sous vide machine do you have available? Given that boiling potatoes whole, in a pot, and mashing them by hand (or with multiple types of machine or hand tool - mixer, food processor, potato-masher) works perfectly well, it feels like an over-complication of a simple process.
    – Ecnerwal
    Commented Aug 22, 2022 at 1:57
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    Well over-blending makes mashed potatoes gummy. So the food processor and blender are out. I do have a handheld masher which I was planning on using with the shredded potatoes. Also the sous vide machine gives me more flexibility and consistently perfect results. Also it means once they are done, they are already sealed in a bag with just the right amount of moisture and won't dry out. So they may be able to produce the same result, but one is easier for me with other added benefits.
    – Nicholas Summers
    Commented Aug 22, 2022 at 2:12
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    >> I have previously tried mashing them in the bag, but ended up missing several cubes of potatoes. Have you considered this but using a rolling pin instead of a manual potato masher?
    – mcalex
    Commented Aug 22, 2022 at 8:14
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    The benefits of sous vide mashed potatoes are 1) no added cooking water as potatoes already contain sufficient water to fully gelatinise all the starches present, and 2) gasses are trapped, preventing loss of volatile flavour compounds - leading to improved texture without waterlogging and stronger potato flavour. @mcalex's suggestion to use a rolling pin is probably the best option if available, you'd just need more vacuum bag length to allow for thorough squeezing.
    – borkymcfood
    Commented Aug 22, 2022 at 18:54
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    Even if you don’t have a River. You might be able to push them through a coarse sieve to get a similar effect
    – Joe
    Commented Aug 22, 2022 at 22:53

3 Answers 3

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Shredding the potatoes raw will release too much calcium and disrupt too many cells, similar to pureeing them.

You can definitely give it a try, though the end result will likely have a firmer gelled texture more suitable for latkes or hash browns. On the plus side, you can salvage the results for those uses.

You could try passing the cooked potatoes through a coarse strainer or sieve if you have those - not as fine, but will prevent major chunks.

The science behind it

Raw potatoes will have certain enzymes active (pectin methyl esterases, 'PMEs') that convert pectins in the potato cell walls from one general state to another - high methoxyl to low methoxyl.

PMEs and calcium naturally present in potatoes are released when the cells are disrupted from cutting, blending, shredding, etc. The pectins get converted and the low methoxyl pectins readily bind with the calcium, forming strong calcium pectinate gels.

Heating inactivates the PMEs, with full inactivation around 80C, which is why cooked potatoes usually do not gum when mashed.

Resources to look into:

  • Potato tuber pectin structure is influenced by pectin methyl esterase activity and impacts on cooked potato texture, Heather A. Ross, Kathryn M. Wright, Gordon J. McDougall, Alison G. Roberts, Sean N. Chapman, Wayne L. Morris, Robert D. Hancock, Derek Stewart, Gregory A. Tucker, Euan K. James, Mark A. Taylor, https://doi.org/10.1093/jxb/erq280
  • Optimization of calcium pectinate gel production from high methoxyl pectin, Hanying Duan,Xiaoyun Wang,Nima Azarakhsh,Chao Wang,Meng Li,Guiming Fu,Xuesong Huang, https://doi.org/10.1002/jsfa.11409
  • Pectin methylesterase catalyzed firming effects on low temperature blanched vegetables, Li Ni, Daniel Lin, Diane M. Barrett, https://doi.org/10.1016/j.jfoodeng.2004.10.009
  • Extraction and characterization of pectin methylesterase from Alyanak apricot (Prunus armeniaca L), M. Ümit Ünal and Aysun Şener, https://doi.org/10.1007%2Fs13197-013-1099-3
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    Great answer. I love it when people add the science.
    – Kingsley
    Commented Aug 23, 2022 at 21:44
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Beside what borkymcfood said about the gluey part, I wouldn't go around increasing the surface area of the potatoes before cooking them for mash.

Whole boiled potatoes are thirsty. When you cook them whole, the starch stays much less hydrated than when they are cut up in small pieces. Then you use a ricer to break them apart while hot (which is easy at that point, the cell walls separate of their own accord) and add the milk. The milk binds well with the starch, and makes a nice cohesive texture.

You can get away with cubed potatoes too, but not as well as with whole ones. But if you shred them first, they might get soggy. I am not entirely sure if this will be the case if you make them in a sealed bag, but there will be juice getting out of the vacuoles, and it might be enough to make them waterlogged in the bag. If you cook shredded potatoes directly in water, they will go soggy for sure. And soggy potatoes do not make smooth, nice mash.

In the end, people rice potatoes because it works. Depending on how frequently you make them, you can decide if you want to invest in a more complex hinged ricer, to stay with a simple stamping one, or just use a fork. You will still get better mash with less effort than cubing or shredding, then doing sous vide, then trying to puree them without blunt force.

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    The prickly dry sensation is not physical drying on the tongue, it's the sensation of astringency from compounds naturally present in the potatoes themselves, including solanine - doi.org/10.1021/acs.jafc.0c04853
    – borkymcfood
    Commented Aug 22, 2022 at 19:02
  • @borkymcfood interesting - do you happen to know why it only happens when the potato is prepared with minimal water contact, such as being cooked or baked whole, and not in other preparations?
    – rumtscho ♦
    Commented Aug 22, 2022 at 19:07
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    absolutely - glycoalkaloids/saponins, of which solanine is a specific compound, are present mainly in the thin layer at and under potato skins, which are left on when baked whole and typically removed for mashing. The premise that minimal water contact leads to astringency from starch is erroneous. Consider French fries, specifically any varieties with the peel on - cooked in a completely water-free environment with the only water source being intracellular, and you'll notice bitter/astringent/slightly acid sour taste focused at the peel sections and not the centre sections.
    – borkymcfood
    Commented Aug 22, 2022 at 19:47
  • I love my potato ricer. I boil potatoes cut in half, then rice them hot with the cut-side down, the skin is left behind. It's far quicker than peeling, cubing, etc. etc. Just be sure to wash the ricer before the potato starch hardens.
    – Kingsley
    Commented Aug 23, 2022 at 21:49
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If you shred them, or even cut them too small, before boiling your finished product will resemble glue more than fluffy mashed potatoes.

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