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added reference ot freezing fruit breaking down cell walls
Fruit is available to the brewer in multiple different forms.
* Whole or sliced fresh - Use a CO2-purged keg or minimize headspace in a carboy. Mold and acetic acid bacteria can grow on the skins of floating fruit <ref name="kohlmorgen"></ref>. ''Brettanomyces'' can also produce acetic acid in the presence of O2, and it is possible that this is the source of acetic acid sometimes found in beers with floating fruit rather than acetic acid bacteria. Some brewers like to swirl the fermenter every few days or to keep the alcohol in contact with the fruit, though some others report no ill effects from not swirling the fermenter (and this is impractical in commercial settings). If using a barrel or larger fermenter, you may try using a punch-down technique. If punching down the fruit, purge the headspace of the vessel with CO2 to avoid oxygen exposure to the beer. Allow the fruit to get fully or possibly even over-ripe (not rotten) for best flavor. Whole fruit may take longer to ferment but it also can give the most complexity <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1123884634306416/?comment_id=1123893237638889&offset=0&total_comments=9&comment_tracking=%7B%22tn%22%3A%22R0%22%7D Thoughts from Raf Soef on using whole fruit in a MTF thread]</ref>
* Whole or sliced frozen - Freezing fruit has a few main potential benefits. First, freezing fruit helps to break down cell walls, which may make the fruit easier to access for yeast and bacteria in the beer<ref>[http://www.ncbi.nlm.nih.gov/pubmed/23670237 "Effects of freezing and thawing on texture, microstructure and cell wall composition changes in papaya tissues." Phothiset S, Charoenrein S. 2014.]</ref>. Freezing fruit can also knock back the microbes present on the fruit. Note however that freezing does not kill all the microbes on the fruit. Finally, freezing fruit allows the brewer (especially the homebrewer) to take advantage of local and seasonal fruits when they may not have a use ready for those fruits in season. Frozen fruits are also available as IQF, or individually quick frozen fruit. IQF fruit is frozen but each berry is distinct rather than a single frozen mass. This allows for easier handling, helps prevent clumping, makes for easier fitting of fruit into small openings in carboys or barrels, and allows screening and removal of bad looking fruit. Defrost frozen fruit in the microwave or in the fridge over night. The fruit doesn't necessarily have to come all the way up to cellaring or room temperature. Adding frozen fruit without thawing it first is probably fine as well. The beer and frozen fruit will come back up to ambient temperatures over night <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1215622131799332/?comment_id=1215820848446127&comment_tracking=%7B%22tn%22%3A%22R%22%7D Conversation with Devin Bell on MTF. 01/17/2016.]</ref>.
* Pureed fresh - pureeing fresh fruit has the benefit of extracting the fruit flavor faster. It also sinks to the bottom of the fermenter <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1172395836121962/?comment_id=1172413292786883&offset=0&total_comments=10&comment_tracking=%7B%22tn%22%3A%22R4%22%7D Conversation with Dara McMains on MTF regarding puree. 11/1/2015.]</ref>, so the problem of floating whole fruit is avoided. Puree can be difficult to rack the beer off of, and more beer may be lost compared to using whole fruit. Some brewers choose to heat pasteurize freshly made puree.
* Aseptic puree - Same as "Pureed Fresh", but has already been pasteurized. This is usually the case for commercially available puree. We recommend [http://www.oregonfruit.com/specialty-fruit-products Oregon Specialty Fruit] or [https://www.perfectpuree.com/ The Perfect Puree] for quality commercial puree.