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Ask the Produce Docs (Commodity)

Do you have information about the best temperatures at which I should store nuts for our retail chain?

Category
  • Dried Fruits & Nuts
  • Nuts
Question

We are a national retail chain interested in the proper postharvest handling of nuts.  Nuts are usually held in our distribution centers (DCs) for about 3-4 weeks, but we do not have a consistent temperature zone established as a best practice.  In some DCs, the nuts are stored at low temperature (34-37F; 1-3C) while in others they are stored with the dry grocery items at 65-80F (18-27C).  At the store level, the nuts are displayed in non-refrigerated area.   Do you have any specific temperature information to help me?

Answer

Since nuts are increasing in popularity, I reviewed the published literature to ensure the most accurate information.  Three sources of information are cited below, but a more extensive reference list on nuts is available at http://ucanr.edu/datastoreFiles/234-2753.pdf.

Important factors for nut quality include drying to low moisture content and packaging in moisture proof bags.  Since nuts in shells are often handled loose, temperature will be important to maintain quality and shelf-life as summarized in Table 1.

These shelf-life estimates take into account information on quality and food safety changes at different temperatures.   The main quality concerns are rancidity (oxidation of lipids leading to off-flavors), darkening (related to initial drying temperature and subsequent storage conditions), mold growth (moisture and temperature dependent), brittleness (moisture content too low), insect infestation, and stale flavor (held too long under the given storage conditions).  The main food safety concerns for nuts are aflatoxins produced by fungi and human pathogenic bacteria (Salmonella sp., Listeria monocytogenes); both food safety aspects are affected by the moisture content and temperature of the nut.  Some nuts, especially peanuts, may cause allergic reactions in some people. 

The moisture content of common nuts in refrigerated storage should be near the following percentages: almonds 6%, Brazil nuts 7%, cashew nuts 8%, coconut 20%, hazelnuts 15%, macadamia nuts 15%, pecans 5%, peanuts 7%, pistachio nuts 7% and walnuts 5%.  The optimum relative humidity of storage varies from 55-70% depending on the moisture content of the nuts, and packaging in moisture-proof containers is recommended to maintain quality. The higher the temperature, the more critical is relative humidity and moisture content. Coconuts and chestnuts have high moisture contents and should be considered more as ‘fresh fruits’.

Nuts in the shell have about 25-50% longer shelf-life than the nutmeats alone; this percentage can vary considerably depending on the particular nut and whether the packaging provides a moisture barrier and/or a low oxygen concentration.  Pieces of nutmeats have about half the shelf-life of the intact nutmeats.  Some roasted nuts have a shelf-life about one fourth that of the raw nutmeats.

In general the optimal storage temperature is 0-10C with relative humidity at 55-70%, depending upon the original moisture content of the nut.

-Marita Cantwell

 

Table 1.  Shelf-life of raw nuts (in shell or intact nutmeats) stored at different temperatures.   Estimates are derived from general published information and the specific references cited. If the nutmeats are packaged, it is assumed that relative humidity is controlled but that oxygen concentrations are not substantially different from air.   It is also assumed the nuts were dried adequately before storage.

 

 

Estimated Shelf-life in months

 

Nut

Type

-10°C

(-14°F)

0°C

(32°F)

10°C

(50°F)

20°C

(68°F)

30°C

(86°F)

References

Almond

Nutmeat

 

10

8

4

 

Labavitch, 2004;
Cornacchia et al., 2012

 

In shell

 

20

16

6

 

Labavitch, 2004
Cornacchia et al., 2012

Brasil nut

Nutmeat

 

6

 

 

 

WFLO, 2008

 

In shell

 

12

 

 

 

WFLO, 2008

Cashew

Nutmeat

 

12

 

6

 

Soares et al., 2012; WFLO, 2008

Chestnut

In shell

Do not freeze

3

0.5

0.25

 

Kader, 2003;
Panagou et al., 2006

Coconut

In shell, no husk

 

2

0.5

 

 

TIS, undated; Siripanich et al., 2011

 

In green husk

 

2

1

0.5

0.25

Maciel et al., 1992; Siripanich et al., 2011

Hazelnut

Nutmeat

 

24

12

 

 

Maness, 2004

 

In shell

 

24

12

 

 

WFLO, 2008

Macadamia

Nutmeat

24

12

12

5

0.75

Cavaletto, 2004; Wall, 2013

Peanut

Nutmeat

24

12

9

4

 

WFLO, 2008; Maness, 2004; Calhoun, 2013

 

In shell

 

12

9

6

 

Maness, 2004; Ortloff, 2009

Pecan

Nutmeat

18

10

 

3

 

Maness, 2004

 

In shell

24

18

9

4

 

WFLO, 2008; Maness, 2004

Pine Nut

Nutmeat

 

 

 

 

 

 

Pistachio

Nutmeat

 

10

3

1

0.25

Arena et al., 2013; Kader & Thompson, 2002

 

In shell, split

 

12

 

 

 

Maskan et al., 1999

Walnut

Nutmeat

 

12

 

3

 

Mexis et al., 2009; Kader and Thompson, 2002

 

In shell

 

12

 

4

 

McNeil, 2013

Average*

 

22.5

13.5

10

4

0.5

 

*The average excludes high moisture chestnuts and coconuts

 

Kader, A.A. and J.F. Thompson. 2002. Postharvest handling systems: Tree nuts.  Ch 32, pp 399-406. In: Kader, A.A. (ed.), Postharvest Technology of Horticultural Crops.  Univ. California Publication 3311.

Kader, A.A., E.J. Mitcham and C. Crisosto. 1998. Dried fruits and nuts: Recommendations for maintaining postharvest quality. http://postharvest.ucdavis.edu/PFfruits/DriedFruitsNuts/.

Harris, L.J. (ed.) 2013. Improving the safety and quality of nuts.  Woodhead Publishing Series in Food Sciences, Tech. and Nutrition Number 250, Woodhead Publishing, Cambridge, UK. 405 pp.

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