The size of pineapples is usually not a good indicator of its quality, meaning that large or small pineapples are not very different, but it's often a good idea to prefer larger ones, because the relative weight of the fruit to the refuse is higher, and you get more "bang for your buck".
Once picked from the plant, pineapples do not ripen further, so you should choose a fruit that emanates a good fragrance, and definitely avoid those too green and those smelling sour or musty.
Choosing a ripe pineapple is essential if you want to reap the most health benefits: studies conducted at the University of Innsbruck in Austria have proven that as fruits (in general) ripen, their antioxidants levels increase substantially.
The process was explained by lead researcher Bernard Kräutler and his team, who worked in conjunction with botanists for years. They found the first decomposition product in leaves: it's a colorless, polar nonfluorescing chlorophyll catabolyte (abbreviated as NCC), containing four pyrrole rings (like chlorophyll and heme groups in hemoglobin).
It appears that this compound gradually replaces chlorophyll not only in the leaves, but also in fruits during the ripening process, with higher concentrations in the peel and outermost pulp layers.
This is macroscopically visible when leaves turn from green to red in autumn (the green color is caused by the presence of chlorophyll).
Here's a quotation from the researchers:
When chlorophyll is released from its protein complexes in the decomposition process, it has a phototoxic effect: when irradiated with light, it absorbs energy and can transfer it to other substances. For example, it can transform oxygen into a highly reactive, destructive form," report the researchers. However, NCCs have just the opposite effect. Extremely powerful antioxidants, they play an important protective role for the plant, and when consumed as part of the human diet, NCCs deliver the same potent antioxidant protection within our bodies." Angew Chem Int Ed Engl. 2007 Nov 19;46(45):8699-8702.After buying, pineapples should be kept at room temperature for a couple of days before serving. We've already mentioned that they won't ripen any further, but this will help them become juicy and tasty.
They can be stored in the fridge, whole, for longer timespans, provided you wrap them in plastic bags, but usually not more than five days.
If you want to store sliced up pineapples, be aware that they will keep for a maximum of three-four days, and should be wrapped in an airtight container with some pineapple juice to retain flavor and a soft texture.
Freezing is generally not recommended: it is very effective for storage, but it greatly reduces the flavor of your fruit.